Prof. Dr.-Ing. Ilona Rolfes

In­sti­tu­te of Micro­wa­ve Sys­tems
Ruhr-Universität Bochum

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  • A Minimally Invasive Monitoring Concept for Plasma-Assisted Surface Treatments in PET Bottles
    Pohle, D. and Mitschker, F. and Jenderny, J. and Rudolph, M. and Schulz, C. and Awakowicz, P. and Rolfes, I.
    2020 50th European Microwave Conference, EuMC 2020 (2021)
    This paper presents a novel approach to plasma monitoring in the context of plasma-assisted surface treatments in PET bottles. In industrial state-of-the-art production of PET-based beverage bottles, a so-called Plasmaline antenna is inserted into the bottle which provides both process gases and microwave excitation to generate the plasma state required for coating or sterilization on its inside. The proposed concept based on the planar multipole resonance probe (pMRP) allows for a non-invasive supervision of the plasma from the outside of the bottle wall. Since plasma and probe head are only separated by dielectric materials in between, the sensor's electric field is able to interact with the plasma and the resonance behavior that occurs can be evaluated and tracked. The performance of the concept regarding changes of the plasma electron frequency and the electron collision frequency are investigated within 3D full-wave simulations in CST Microwave Studio. Measurements of an argon plasma are presented as a proof-of-concept, with the plasma being monitored from the plasma-remote side of a PET bottle section. © 2021 EuMA.
    view abstract10.23919/EuMC48046.2021.9338200
  • Aperture Synthesis Method to Investigate on the Reflection Properties of Typical Road Surfaces
    Jebramcik, J. and Rolfes, I. and Barowski, J.
    2020 50th European Microwave Conference, EuMC 2020 (2021)
    In this contribution, a millimeter wave FMCW (frequency modulated continuous wave) radar is utilized to investigate the surface reflection of an asphalt sample at 80 GHz. Since the reflection properties of such a rough surface usually strongly depend on the characteristics of the antenna (i.e. opening angle, spot on sample) that is used in the measurement, a more generalized approach is presented here. Based on the backprojection algorithm, the measurement data, obtained by a relatively undirected antenna, are used to infer the reflection properties for different antenna systems with other radiation patterns. Exemplary measurement results are presented in this paper, proving the suitability of the proposed method. © 2021 EuMA.
    view abstract10.23919/EuMC48046.2021.9338033
  • Beam divergence reduction of vortex waves with a tailored lens and a tailored reflector
    Hassan, M.H. and Sievert, B. and Svejda, J.T. and Ahmed, A.M. and Barowski, J. and Rennings, A. and Rolfes, I. and Sezgin, A. and Erni, D.
    IEEE Access 9 (2021)
    Reducing the strong beam divergence inherent to Orbital Angular Momentum waves (also known as OAM waves or vortex waves), a tailored lens and a tailored reflector are presented in this study. The generation of the OAM waves is accomplished by a Uniform Circular Patch Antenna Array (UCA) operating at 10 GHz. Here, the tailored lens and reflector are set up by two correspondingly designed shape functions rotated around the antenna's center axis in broadside direction (i.e. body of revolution approach). Initially, the tailored lens is introduced to be compared to the UCA in the presence and absence of the conventional lens separately. Upon the usage of the tailored lens, a gain improvement of 5.8 dB has been obtained in the simulation compared to a gain of 4.8 dB in the measurement. On the other hand, the tailored reflector is set under the same procedure to be compared also to the UCA with and without a conventional reflector. Both of the reflectors are simulated under idealized conditions with the aid of an OAM impressed field source used as an emitter for a meaningful comparison. The simulated gain has shown a better performance accomplished by the tailored reflector as the height r0 reaches a level less than 1.5 λ as well as the opening angle θ is less than 38° (given an UCA with an element separation distance d=λ/2). Furthermore, three different ground plane shapes with realistic UCA are applied for the simulation procedure where each of them is perturbing the radiation of the reflector. All of the lenses and the reflectors are manufactured and later measured in an anechoic chamber to undergo a comparison with the simulated results. This article demonstrates that the vortex waves need a tailored lens or a tailored reflector to decrease the beam divergence effectively especially when the radius of the UCA becomes increasingly large. © 2013 IEEE.
    view abstract10.1109/ACCESS.2021.3050043
  • Characterization of Dielectric Materials by Sparse Signal Processing with Iterative Dictionary Updates
    Thanthrige, U.S.K.P.M. and Barowski, J. and Rolfes, I. and Erni, D. and Kaiser, T. and Sezgin, A.
    IEEE Sensors Letters 4 (2020)
    Estimating parameters and properties of various materials without causing damage to the material under test (MUT) is important in many applications. Thus, in this letter, we address MUT's parameter estimation by wireless sensing. Here, the precision of the estimation depends on the accurate estimation of the properties of the reflected signal from the MUT (e.g., number of reflections, their amplitudes, and time delays). For a layered MUT, there are multiple reflections, and due to the limited bandwidth at the receiver, these reflections superimpose with each other. Since the number of reflections coming from the MUT is limited, we utilize sparse signal processing (SSP) to decompose the reflected signal. In SSP, a so called dictionary is required to obtain a sparse representation of the signal. Here, instead of a fixed dictionary, an iterative dictionary-update technique is proposed to improve the estimation of the reflected signal. To validate the proposed method, a vector network analyzer (VNA)-based measurement setup is used. It turns out that the estimated dielectric constants of the MUTs are in close agreement with those reported in literature. Further, the proposed approach outperforms the state-of-the-art model-based curve-fitting approach in thickness estimation. © 2017 IEEE.
    view abstract10.1109/LSENS.2020.3019924
  • Considerations regarding simulator design for electromagnetic measurement systems
    Garten, O. and Barowski, J. and Rolfes, I.
    Proceedings of the 2020 IEEE International Conference on Computational Electromagnetics, ICCEM 2020 (2020)
    In this paper a concept for a simulation specialized in electromagnetic wave interaction on multiple scales is proposed. The approach is based on the complex source point beam (CSPB) expansion of the electromagnetic field. Based on the CSPB expansion, a domain decomposition which enables efficient multi scale simulations is used. Furthermore, each of the basis functions for the expansion is highly directive which has significant advantages, because it reduces the amount of interactions that need to be considered. © 2020 IEEE.
    view abstract10.1109/ICCEM47450.2020.9219331
  • Estimation of the relative permittivity from the molecular structure of polymers used in automotive industries
    Bonfig, T. and Körner, E. and Jebramcik, J. and Kroll, L. and Rolfes, I. and Jan Barowski
    Materials Research Express 7 (2020)
    To scan a vehicle's environment frequency modulated continuous wave (FMCW) radar sensors are essential. The implementable driver assistance systems based on these sensors increase the comfort of an automobile. When integrating them into the car, the radar sensor's cover must be taken into account. These parts serve as protection against external chemical and mechanical influences, but they should also support the vehicle design and appearance. Usually, painted polymer components are used as a radome. Depending on their material parameters (i.e. relative permittivity and loss-tangent) polymer covers lead to reflections and absorption, which may impair the radar performance, if they are not properly designed from a microwave point of view. For an appropriate design procedure, the polymer properties, have to be known precisely beforehand or need to be analyzed in realistic experimental configurations. Within this paper it is shown by measurements around the 80 GHz automotive radar bands and calculations based on the polymers repeating unit that the relative permittivity can be estimated from knowledge of the molecule structure. This allows the calculation of the relative permittivity of polymer molecules that have not yet been measured in the W-band at 80 GHz at a very early stage of the design process. Additionally it is shown that it has to be taken into account if the polymer is semi-crystalline or amorphous. Furthermore, the density or crystallinity has to be known. © 2020 The Author(s). Published by IOP Publishing Ltd.
    view abstract10.1088/2053-1591/abcb3b
  • Extracting the Features of the Shallowly Buried Objects using LeNet Convolutional Network
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    14th European Conference on Antennas and Propagation, EuCAP 2020 (2020)
    The convolutional neural networks are considered as the best artificial intelligence algorithms for image classification problems. Generally, a ConvNet requires a very large number of images to be trained well and to achieve the best results. This paper investigates the implementation of the LeNet-5 convolutional network (ConvNet) for images classification using a small dataset. The dataset of interest compromises images of buried objects obtained by a ground penetrating radar (GPR), which is considered as an efficient tool for detecting and defining buried objects. One of the main problems facing this classification task is the limited available data. In deep learning algorithms, the ConvNet is usually trained using very large datasets, therefore the transfer learning has to be employed, as it is considered as a very important tool in deep learning when dealing with limited datasets. The LeNet-5 has been deployed and trained on the Fashion-MNIST dataset, and the learned features have been transferred to our GPR dataset. The network performance has been monitored and the classification results show a high degree of precision and accuracy. © 2020 EurAAP.
    view abstract10.23919/EuCAP48036.2020.9135701
  • FPGA Based Accelerator for Buried Objects Identification
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2020 43rd International Conference on Telecommunications and Signal Processing, TSP 2020 (2020)
    The convolutional neural networks(ConvNets) have emerged during the past few years due to various advancements in the field of artificial intelligence. They have participated in different applications and complex problems and gained significant success in images classification tasks. As these algorithms require intensive operations, different researches have been conducted to provide various hardware accelerators for these algorithms. Different studies have investigated the implementation of the graphic processing units(GPUs) and application-specific integrated circuits (ASICs) for decreasing the processing time of the ConvNets. In this research, the authors present a fast framework for GPR images classification based on the Xilinx PYNQ platform. This framework offers high-level language integration to facilitate the design of the projects. Various experiments have taken place to prepare the GPR dataset and the designed ConvNet has been integrated on PYNQ to perform real-time calculations. The obtained results indicate an outstanding time processing improvement while preserving the classification accuracy. © 2020 IEEE.
    view abstract10.1109/TSP49548.2020.9163583
  • Guest Editorial
    Rolfes, I. and Pohl, N.
    IEEE Transactions on Microwave Theory and Techniques 68 (2020)
    view abstract10.1109/TMTT.2020.2993940
  • Hardware/Software Co-design for the Signal Processing of Dielectric Materials Characterization
    Kamaleldin, A. and Wagner, J. and Rolfes, I. and Barowski, J. and Goehringer, D.
    2020 3rd International Workshop on Mobile Terahertz Systems, IWMTS 2020 (2020)
    This paper presents a novel signal processing implementation for a dielectric materials characterization method using the hardware/software co-design methodology for application acceleration and rapid deployment on heterogeneous embedded platforms. The dielectric materials characterization method uses Frequency Modulated Continuous Wave radar systems for measurement purposes. Since the dielectric materials characterization method is intended to be used in a mobile materials characterization setup. The required signal processing algorithm of the materials characterization method is implemented on a Xilinx Zynq Ultrascale+ Multiprocessor System-on-Chip. Whereas, the intensive computing part of the algorithm is implemented on the hardware partition using high level synthesis design methodology for purposes of acceleration. The remaining parts of the algorithm are executed in software on the processing system part of the multiprocessor system on chip platform. The execution time, hardware resources utilization and energy consumption of the proposed co-design are determined experimentally. Furthermore, several optimization techniques are explored in order to reduce the total energy consumption and increase the data transfer bandwidth between the hardware and software partitions. The experimental results show a maximum speed up of 7.25 for the proposed co-design over the software reference model with an energy consumption less than 10 Joule. © 2020 IEEE.
    view abstract10.1109/IWMTS49292.2020.9166402
  • Investigation on the scattering characteristics and unsupervised clustering of 3D printed samples
    Elsaadouny, M. and Barowski, J. and Jebramcik, J. and Rolfes, I.
    International Journal of Microwave and Wireless Technologies 12 (2020)
    In this work, the scattering characteristics of 3D-printed samples are being investigated by using a single-polarized and a cross-polarized radar system. The 3D-printed technology participates in a wide range of applications nowadays. The idea of synthetic aperture radar (SAR) has been utilized to investigate the reflected electromagnetic energy from the 3D-printed samples by setting each of the radar systems in a fixed position and the mounting sample on an x-y positioning table which has been used to achieve rectangular-scan mode for SAR. The data have been ported and processed by the matched filter approach. For better image interpretation, the data have been further processed by the median filter in order to reduce noise level while preserving the main image details. Afterwards, the data have been further investigated for determining and classifying any possible defects. This process has been accomplished by deploying the unsupervised learning concept to cluster the SAR responses into two groups, compromising the defected positions responses and the non-defected responses. The obtained results of both radar sensors have been compared and evaluated using different quality assessment factors. Moreover, unsupervised learning techniques have been investigated and the obtained results show a high degree of efficiency in clustering the SAR responses. Copyright © Cambridge University Press and the European Microwave Association 2020.
    view abstract10.1017/S1759078720000823
  • Millimeterwave Radar Systems for In-Line Thickness Monitoring in Pipe Extrusion Production Lines
    Jebramcik, J. and Rolfes, I. and Pohl, N. and Barowski, J.
    IEEE Sensors Letters 4 (2020)
    This letter presents algorithms and considerations for the applicability of millimeter wave radar systems as monitoring sensors in the field of plastic pipe extrusion. Since a constant wall thickness of the pipe is a major quality factor of the product, monitoring systems that in-line measure the thickness during the extrusion process are commonly used. Modern ultrawideband radar systems achieve target resolutions in the range of millimeters, allowing competition with well-established methods, such as ultrasound sensors, and even expensive photonic Terahertz devices. The authors describe a novel accurate and efficient method to measure the pipe-wall's thickness based on frequency domain evaluation of the material reflection. The general feasibility of W-band radar sensors, as well as the accuracy of the proposed method, is demonstrated by measurements using a moderate size polyvinyl chloride pipe. © 2017 IEEE.
    view abstract10.1109/LSENS.2020.2991778
  • Simulation and optimization of the design of focusing dielectric lenses based on cartesian ovals with physical optics
    Garten, O. and Barowski, J. and Rolfes, I.
    2020 International Workshop on Antenna Technology, iWAT 2020 (2020)
    This paper presents the design of a focusing dielectric lens, which is described by a so-called Cartesian oval. The mathematical model of Cartesian ovals is introduced briefly. Next, a physical optics (PO) approach for the simulation of the electric field outside of the antenna is presented. Simulation results at 80 GHz are shown. The agreement between a full wave reference method and the proposed method is good, especially in the focal region. The simulation time is decreased significantly by the asymptotic PO approach compared to the finite integration technique. Eventually, a lens design is optimized with the PO to achieve the desired focal point. © 2020 IEEE.
    view abstract10.1109/iWAT48004.2020.1570609732
  • The 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications [Conference Reports]
    Rolfes, I.
    IEEE Microwave Magazine 21 (2020)
    view abstract10.1109/MMM.2019.2952038
  • The Planar Multipole Resonance Probe: A Minimally Invasive Monitoring Concept for Plasma-Assisted Dielectric Deposition Processes
    Pohle, D. and Schulz, C. and Oberberg, M. and Awakowicz, P. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 68 (2020)
    In this article, a novel minimally invasive approach to plasma monitoring in the challenging environment of dielectric deposition processes based on the planar multipole resonance probe (pMRP) is presented. By placing the sensor on the plasma-remote side of a dielectric substrate to be coated, perturbations of the process due to its presence can be significantly reduced. Since the electric field of the sensor is able to penetrate dielectric layers, a plasma supervision through the substrate is enabled. To investigate the effect of increasing coating thicknesses on the measurement performance for a broad spectrum of materials and plasma conditions, the results of extensive 3-D full-wave simulations performed with CST Microwave Studio are evaluated. Finally, real-time monitoring results of an argon-oxygen plasma during a sputter deposition with aluminum oxide on a polyethylene terephthalate (PET) film substrate together with a comparison to external process parameters are presented. The results demonstrate both the applicability of the proposed concept and its insensitivity to additional dielectric coatings. © 1963-2012 IEEE.
    view abstract10.1109/TMTT.2020.2974835
  • A 3D printed elliptical mirror for material characterization using FMCW transceivers
    Wagner, J. and Barowski, J. and Rolfes, I.
    Asia-Pacific Microwave Conference Proceedings, APMC 2018-November (2019)
    Elliptical mirrors can be used to focus electromagnetic waves without losses that occur during propagation through dielectric lenses. As common milled mirrors have a high weight and require time-consuming productions steps, a 3D printed elliptical mirror, coated with a copper spray, is analyzed in this paper regarding its suitability for microwave applications. It can be shown that both mirrors can reach focus diameters below 1 cm, which is suitable for applications like material charakterization. Additionally, this paper presents radar measurement results at 145 GHz that compares the 3D printed mirror with a common milled one. © 2018 IEICE
    view abstract10.23919/APMC.2018.8617212
  • A compact measurement setup for in-situ material characterization in the lower THz range
    Barowski, J. and Jebramcik, J. and Alawneh, I. and Sheikh, F. and Kaiser, T. and Rolfes, I.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    Frequency Modulated Continuous Wave radar systems offer a very large dynamic measurement range, while at the same time they can be fabricated very compact and cost efficient. Due to this, FMCW-sensors are a feasible alternative to costly measurement equipment like vector network analyzers. Applying calibration techniques and algorithms from the VNA domain, they can also be used to characterize materials with very high precision. At the same time, the short measurement time allows their use in mobile high precision measurement setups. This paper presents such a mobile setup that is easily calibrated an can be used for in-situ material parameter estimation and data collection for e.g. channel models. For this purpose, a SiGe-radar system in the lower THz range from 200 GHz to 250 GHz is used. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823700
  • A convolutional neural network for the non-destructive testing of 3D-printed samples
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019-September (2019)
    The three-dimensional printing is a very important technology that participates in many applications. In this paper, we present an approach for the Non-Destructive Testing (NDT) of the three dimensional printed objects. This methodology solves the image classification problem by using Convolutional Neural Networks (CNN). The network has been trained by a large number of synthetic aperture radar (SAR) images obtained by 80 GHz radar system. The proposed solution has been used for testing different data sets for monitoring the performance under different scenarios, and the obtained results show a high degree of accuracy regarding the defected samples classification. © 2019 IEEE.
    view abstract10.1109/IRMMW-THz.2019.8874445
  • A Novel Calibration Technique for FMCW Radar Systems Enabling Material Characterization in Variable Distances
    Jebramcik, J. and Rolfes, I. and Barowski, J.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this contribution, a calibration method for millimeter wave FMCW (frequency modulated continuous wave) radar is presented. The proposed technique utilizes the potential of an adjustable ramp duration to extend the validity range of the calibration measurement at a single position and enables the characterization of material samples in varying distances. Exemplary measurement results in the W-band are presented, proving the accuracy of the method. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880110
  • A SAR Image Enhancement Algorithm using the Discrete Wavelet Transform
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2019 IEEE 10th Annual Information Technology, Electronics and Mobile Communication Conference, IEMCON 2019 (2019)
    Synthetic aperture radar (SAR) images are badly affected by the existence of the speckle noise. In this research, we present an algorithm for despeckling the SAR images. This algorithm makes efficient use of the discrete wavelet transform (DWT) and the directional smoothing filter (DSF). The DWT has been widely used in image denoising applications, while the DSF is well known for enhancing the SAR images in the presence of speckle noise. The efficiency of the combined algorithm has been demonstrated for both real and simulated speckled SAR images at different noise variances, and the obtained results have been compared to the results acquired while applying only DWT, DSF and other traditional methods. Moreover, the quality investigation has been performed to emphasize the algorithm efficiency. © 2019 IEEE.
    view abstract10.1109/IEMCON.2019.8936169
  • A stacked planar sensor concept for minimally invasive plasma monitoring
    Pohle, D. and Schulz, C. and Oberberg, M. and Friedrichs, M. and Serwa, A. and Uhlig, P. and Oberrath, J. and Awakowicz, P. and Rolfes, I.
    Asia-Pacific Microwave Conference Proceedings, APMC 2018-November (2019)
    A novel advanced design of the planar multipole resonance probe (pMRP) using LTCC-technology is investigated in this contribution. Integrated into the reactor wall, the planar sensor structure enables a minimally invasive in-situ plasma monitoring. Due to the ceramic substrate material, a substantial improved resistance against high temperatures can be achieved, extending the potential fields of application. The used multilayer structure with vertically stacked components ensures a high level of integration and further enhances the mechanical robustness leading to an industry compatible plasma sensor design. The probe is investigated within 3D electromagnetic simulations and its applicability is demonstrated by measurements in a double inductively coupled plasma (DICP). © 2018 IEICE
    view abstract10.23919/APMC.2018.8617552
  • Antenna pattern characterization with an industrial robot assisted FMCW radar system
    Piotrowsky, L. and Bernhardt, V. and Barowski, J. and Rolfes, I. and Pohl, N.
    Asia-Pacific Microwave Conference Proceedings, APMC 2019-December (2019)
    Using an ultra-wideband frequency modulated continuous wave (FMCW) radar and a 7 degree of freedom robot, the antenna pattern of a highly directive dielectric lens antenna is investigated. First a procedure for the determination of the frequency dependent antenna pattern, using the intermediate frequency signal of an FMCW radar, is presented. Consequently, the robotic measurement setup is used to measure the E-and H-plane of the antenna under test. The determined radiation pattern is compared with simulation results, indicating an overall good agreement. © 2019 IEEE.
    view abstract10.1109/APMC46564.2019.9038798
  • Asymptotic Simulation Methods as Forward Models in Multilayer Material Characterization Applications
    Vogt, S. and Garten, O. and Jebramcik, J. and Barowski, J. and Rolfes, I.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this paper a geometrical optics and a physical optics approach are presented as forward models for multilayer problems. The simulation results are validated by measurements and a full wave simulation. The used measurement system is based on a frequency modulated continuous wave radar operating from 68GHz to 92GHz. A matching pursuit decomposition is used to evaluate the relative permittivity and the thickness of the layers to compare the different simulations and the measurement. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880112
  • Characterization of layered dielectric materials using ultra-wideband FMCW-radar measurements
    Jebramcik, J. and Barowski, J. and Rolfes, I.
    Asia-Pacific Microwave Conference Proceedings, APMC 2018-November (2019)
    In this paper ultra-wideband frequency modulated continuous-wave (FMCW) radar is used to investigate the properties of layered materials. The transceiver performs very accurate and fast measurements in the mm-wave region between 68 GHz and 92 GHz. Applying a Matching Pursuit Decomposition on the fast-time echo data, the reflection coefficients of the material sample are extracted. Using this information, the dielectric properties as well as the layer thickness can be evaluated. © 2018 IEICE
    view abstract10.23919/APMC.2018.8617322
  • Editorial
    Perregrini, L. and Pedro, J.C. and Chen, W. and Michael Cheng, K.-K. and Li, C. and Ma, K. and Momeni, O. and Peng, Z. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 67 (2019)
    view abstract10.1109/TMTT.2018.2890778
  • Emulation of Spatially Distributed Plasma Density Profiles in 3D Electromagnetic Field Simulations
    Hattenhorst, B. and Pohle, D. and Schulz, C. and Rolfes, I. and Musch, T.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this contribution, we introduce three dimensional electromagnetic field simulations for spatially distributed plasma density profiles. Basis for these simulations is a macro-based generation of a locally discretized and dispersive plasma environment that ensures a fast and parameterizable creation while keeping computational time reasonable in simulation tools like CST Microwave Studio. Moreover, measurements with a multipole resonance probe inside of a double inductively coupled plasma reactor confirm the introduced emulation approach. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880104
  • Humanitarian Microwave Imaging Enhancement and Classification of Shallowly Buried Objects
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2019 IEEE 10th Annual Information Technology, Electronics and Mobile Communication Conference, IEMCON 2019 (2019)
    The ground penetrating radar (GPR) is one of the promising tools for investigating the shallowly buried objects. This paper aims to solve the problem of the strong clutter reflections associated with the GPR images, and also classify the detected targets to differentiate between different buried objects. First, the implemented algorithm tends to remove the strong background bounce and clutter originated in the non-homogenous region under test by combining two levels of clutter reduction techniques. The first level consists of applying the Moving Average Background Subtraction (MA-BS) method to remove the strong ground reflections and emphasize the target reflection. The second level consists of a combined algorithm which implements the DC-offset removal and the Subtract and Weight (SaW) method for further reduction of the clutter level. The theoretical and mathematical formulation is presented and the acquired results have been investigated for evaluating the implemented method. After reducing the clutter to the lowest possible level and acquiring the images of the buried objects, a K- nearest neighbour (KNN) classifier has been implemented to classify the GPR images. The KNN has been trained to solve this classification problem by a large number of GPR images. After preparing the training data, the data with the corresponding labels have been used for training the KNN and afterwards, the algorithm has been tested and the obtained results showed a good accuracy in objects classification. © 2019 IEEE.
    view abstract10.1109/IEMCON.2019.8936165
  • Investigation on Optical Methods for Multi Scale Electromagnetic Simulations
    Vogt, S. and Jebramcik, J. and Garten, O. and Barowski, J. and Rolfes, I.
    GeMiC 2019 - 2019 German Microwave Conference (2019)
    In this paper a ray tracer based on a shooting and bouncing ray (SBR) technique is presented using an optimization algorithm for precise phase calculation of the channel impulse response, which is mandatory for multi scale simulations. The radiation pattern of the antenna is computed by a full wave simulation in order to calculate the propagating wavefront. The complex open circuit voltage of the antenna is used for modelling the channel impulse response to get the accurate interference phenomena of the received waves. The algorithm is verified by comparison with a commercial full wave simulator. It is also shown that the optimization approach does not only offer high precision, but also enables fast ray tracing, which allows accurate and fast multi scale electromagnetic simulations. © 2019 IMA - Institut fur Mikrowellen- und Antennentechnik e.V.
    view abstract10.23919/GEMIC.2019.8698120
  • Millimeter wave SAR imaging for the non-destructive testing of 3D-printed samples
    Elsaadouny, M. and Barowski, J. and Jebramcik, J. and Rolfes, I.
    Proceedings of the 2019 21st International Conference on Electromagnetics in Advanced Applications, ICEAA 2019 (2019)
    This paper provides a method for the non-destructive testing (NDT) of 3D printed samples, based on synthetic aperture radar (SAR) imaging. The 3D-printed technology has gained a wide popularity and importance as it contributes in different applications. The dependency on this technology nowadays leads to proposing different methods for safely testing the 3D samples. In this research, the NDT has been achieved by using microwave imaging. The tested sample has been placed on a positioning table which has been used to achieve a rectangular-scan mode for the SAR imaging. The gathered SAR measurements have been processed by the matched filter technique for image formation. The obtained SAR images of the sample inner structure have been investigated to determine any possible defects within the structure. The algorithm has been used to test a sample with a pre-designed inner defect, and the obtained SAR images show a high precision in detecting the inner defect. © 2019 IEEE.
    view abstract10.1109/ICEAA.2019.8879272
  • Millimeter Wave Short Range SAR Imaging using Cross-Polarized Radar System
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2018 IEEE 9th Annual Information Technology, Electronics and Mobile Communication Conference, IEMCON 2018 (2019)
    In this work measurement results from a polarimetric millimeter wave radar measurement setup are presented. A cross-polarized antenna is used for rectangular-scan mode for the synthetic aperture radar, and the signal processing is achieved by a 2D and 3D matched filter approach. The used radar system has separate transmit and receive channels, which can be combined using an orthogonal mode transducer. The mechanical setup of the experiments is based on a stationary antenna, an x-y positioning table and the object under test. Different measurements were done in order to investigate the imaging performance and the obtained point spread function using rectangular synthetic apertures arrays. The mathematical model for this short range imaging is illustrated briefly in this paper, and the signal processing algorithm is presented based on the 2D/3D matched filtering. The matched filter is one of the most straight forward methods, but at the same time it is undeniably computationally complex, however, in our algorithm it has been ported to run on Graphical Processing Unit(GPU) instead of a standard CPU, to achieve significant speedups. © 2018 IEEE.
    view abstract10.1109/IEMCON.2018.8615032
  • Minimally Invasive Supervision of Plasma-assisted Dielectric Deposition Processes
    Pohle, D. and Schulz, C. and Oberberg, M. and Awakowicz, P. and Rolfes, I.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    This paper introduces a minimally invasive in-situ plasma monitoring concept suited for the challenging conditions in dielectric deposition processes. Based on the so-called stacked planar multipole resonance probe (spMRP), the sensor is placed directly on the plasma-remote side of a dielectric substrate to be coated, thus minimizing its influence on the process. The sensor's electric field penetrates both substrate and deposited dielectric layers and couples into the plasma. This enables an effective supervision of the plasma parameters required for process control at the point of highest interest. The effect of increasing coating thicknesses on the measurement performance is investigated within 3D electromagnetic field simulations. Final measurements in an argon-oxygen plasma depositing aluminium oxide confirm both the general suitability of the proposed concept as well as the insensitivity to additional dielectric coatings. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880124
  • Non-Destructive Testing of 3D-printed Samples based on Machine Learning
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    The three dimensional printing is a very important technology that participates in many applications. In this paper, we present an approach for the Non-Destructive Testing (NDT) of the three dimensional printed objects. This methodology solves the image classification problem by using the Neural Networks as they are capable of making good decisions and classifying images by proper training. The network has been trained by a large number of images of the tested sample layers. The proposed solution has been used for testing different sets of actual data for monitoring the performance under different scenarios, and the obtained results show a high degree of accuracy regarding image classification and defect detection. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880141
  • Radar Based Material Characterization at 145 GHz Utilizing an Ellipsoidal Reflector
    Jebramcik, J. and Barowski, J. and Wagner, J. and Rolfes, I.
    2019 49th European Microwave Conference, EuMC 2019 (2019)
    Thiscontribution presents a method for the characterization of thin dielectric materials based on frequency modulated continuous wave (FMCW) radar. The transceiver allows precise measurements in the frequency range between 122 GHz and 169 GHz. Using an elliptical mirror, the radiation is focused on the material, achieving a small beam diameter and plane wave fronts. The time domain material measurements are evaluated by means of Matching Pursuit Decomposition (MPD). Thus, the dielectric properties as well as the layer thickness can be determined. © 2019 European Microwave Association (EuMA).
    view abstract10.23919/EuMC.2019.8910803
  • Spatial Identification of Dielectric Properties using Synthetic Aperture Radar
    Barowski, J. and Jebramcik, J. and Wagner, J. and Pohl, N. and Rolfes, I.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    This contribution presents a methodology and a measurement setup for spatially resolved material characterization. For this purpose, calibrated millimeter-wave (mmWave) frequency modulated continuous wave (FMCW) radar systems, operating up to 250 GHz, are utilized. The calibration scheme allows for a systematic error correction comparable to a vector network analyzer (VNA). A synthetic aperture radar (SAR) measurement is used to generate a focused 3-dimensional image with very high resolution. A precise spatial distribution of the material parameters is obtained by a novel combination of the imaging and material parameter extraction algorithms. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880121
  • Synthetic Aperture Radar Imaging Using MIMO Frequency Modulated Continuous Wave Sensors
    Wagner, J. and Dahl, C. and Rolfes, I. and Barowski, J.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this paper, the usage of MIMO Frequency Modulated Continuous Wave (FMCW) radar sensors in Synthetic Aperture Radar (SAR) applications is investigated. MIMO sensors use multiple transmitter antennas and receiver antennas to perform multiple measurements simultaneously in order to - among other purposes - reduce the time of measurement series. It could be displayed that MIMO measurements can be used to increase the step size of a synthetic aperture without having a negative impact on the SAR image. Thus, the SAR measurement time can be reduced by a factor up to the number of MIMO channels, depending on the used MIMO array geometry. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880115
  • Synthetic aperture radar surveillance of conveyed materials at 144 GHz
    Wagner, J. and Rolfes, I. and Barowski, J.
    Asia-Pacific Microwave Conference Proceedings, APMC 2019-December (2019)
    This paper presents a measurement method using Synthetic Aperture Radar (SAR) for the surveillance of bulk materials moving on a conveyor belt. As this concept has to be suitable for realtime monitoring in industrial facilities, the signal processing is able to calculate more than ten SAR images per second. This is achieved using the efficient backprojection algorithm and appropriate shifting of the image area. The velocity of the belt is determined in advance by high precision corner reflector measurements. Additionally, this paper displays results from measurements performed by the presented measurement systems using a Frequency Modulated Continuous Wave (FMCW) radar sensor at 144 GHz to prove the suitability for the desired purpose. © 2019 IEEE.
    view abstract10.1109/APMC46564.2019.9038397
  • The Subsurface Objects Classification using a Convolutional Neural Network
    Elsaadouny, M. and Barowski, J. and Rolfes, I.
    2019 IEEE 10th Annual Information Technology, Electronics and Mobile Communication Conference, IEMCON 2019 (2019)
    The artificial intelligence has been witnessing a monumental growth in bridging the gap between the capabilities of humans and machines. The advancements in computer vision with deep learning have been constructed primarily over the well-known algorithm, which is the convolutional neural network (CNN). The CNN is considered as the best artificial intelligence algorithm for image classification problems. In this paper, we present a CNN for classifying the shallowly buried objects detected by a ground penetrating radar (GPR) system. The GPR is one of the promising tools for investigating the shallowly buried objects. One of the main problems that hinder the GPR, is the strong reflections encountered from the surface and other buried unwanted objects. Therefore, the GPR requires suitable image processing and clutter reduction algorithms to eliminate the clutter and enhance the objects responses. The processed GPR images include responses from different objects and to differentiate between these objects, a CNN has been implemented for this purpose. The presented CNN consists of 3 convolutional layers and each of these layers implements filters which scan the whole input image. Afterwards, the output of each layer has been processed using the rectified linear unit (ReLU) activation function followed by a max-pooling layer. The output of the last layer has been directed as an input to the final output layer which produces a certain probability for each class output using the softmax function. The CNN has been trained by the processed GPR images and the optimization has been accomplished using the Adam optimizer. The obtained performance curves show a high degree of accuracy in classifying the GPR images. © 2019 IEEE.
    view abstract10.1109/IEMCON.2019.8936250
  • A compact and broadband feeding structure for in-situ plasma probe measurements
    Schulz, C. and Rolfes, I.
    Asia-Pacific Microwave Conference Proceedings, APMC (2018)
    A compact and broadband symmetrization for in-situ plasma diagnostics is presented in this paper. Based on the maximum dimensions of the applied multipole resonance probe (MRP), a 5.8 mm by 33 mm stepped tapered balun is integrated into the holder of the probe. It possesses a return loss better than 30 dB and an insertion loss below 0.25 dB in conjunction with a high symmetry from 0.2 to 6 GHz. Hence, an undisturbed resonance behavior can be evaluated to calculate internal plasma parameters by one reflection measurement. The balun is investigated by detailed simulations in CST Microwave Studio and by measurements of a back-to-back transition. Additional measurements within an argon-oxygen plasma prove the suitability of the integrated balun. © 2017 IEEE.
    view abstract10.1109/APMC.2017.8251501
  • A Newly Developed mm-Wave Sensor for Detecting Plaques of Arterial Vessels
    Vogt, S. and Detert, M. and Wagner, D. and Wessel, J. and Ramzan, R. and Nimphius, W. and Ramaswamy, A. and Guha, S. and Wenger, C. and Jamal, F.I. and Eissa, M.H. and Schumann, U. and Schmidt, B. and Rose, G. and Dahl, C. and Rolfes, I. and Notzon, G. and Baer, C. and Musch, T.
    Thoracic and Cardiovascular Surgeon 66 (2018)
    Background Microcalcifications within the fibrous cap of the arteriosclerotic plaques lead to the accrual of plaque-destabilizing mechanical stress. New techniques for plaque screening with small detectors and the ability to differentiate between the smooth and hard elements of plaque formation are necessary. Method Vascular plaque formations are characterized as calcium phosphate containing structures organized as hydroxylapatite resembling the mineral whitlockite. In transmission and reflexion studies with a simple millimeter wave (mm-wave)-demonstrator, we found that there is a narrow window for plaque detection in arterial vessels because of the tissue water content, the differentiation to fatty tissue, and the dielectric property of air or water, respectively. Result The new sensor is based on a sensing oscillator working around 27 GHz. The open-stub capacitance determines the operating frequency of the sensor oscillator. The capacitance depends on the dielectric properties of the surrounding material. The sensor components were completely built up in surface mount technique. Conclusion Completed with a catheter, the sensor based on microwave technology appears as a robust tool ready for further clinical use. © 2018 Georg Thieme Verlag KG Stuttgart, New York.
    view abstract10.1055/s-0037-1606318
  • A simulation concept based on the FDFD method for ground penetrating radar used in humanitarian demining
    Jebramcik, J. and Barowski, J. and Pohle, D. and Baer, C. and Rolfes, I.
    European Microwave Week 2017: "A Prime Year for a Prime Event", EuMW 2017 - Conference Proceedings; 14th European Microwave Conference, EURAD 2017 2018-January (2018)
    In this paper a simulator based on the finite-difference frequency-domain method (FDFD) is presented, allowing an effective and accurate performance estimation of ground penetrating radar in humanitarian demining. After validating the implemented algorithm, the detectability of shallow buried improvised explosive devices (IEDs) is simulated and analyzed. The backprojection algorithm is used to compensate range migration of the ground echoes, improving the signal strength of the IEDs. Subsequently, the impact of surface roughness on the unfocused and focused echo profiles is investigated. © 2017 European Microwave Association.
    view abstract10.23919/EURAD.2017.8249141
  • An advanced high-temperature stable multipole resonance probe for industry compatible plasma diagnostics
    Pohle, D. and Schulz, C. and Rolfes, I. and Oberberg, M. and Awakowicz, P. and Serwa, A. and Uhlig, P.
    GeMiC 2018 - 2018 German Microwave Conference 2018-January (2018)
    In this contribution the development of an advanced, high-temperature stable plasma sensor based on the multipole resonance probe (MRP) is presented. Using low temperature co-fired ceramics (LTCC) as substrate material, together with a multilayer structure, provides resistance against high temperatures as well as a sufficient mechanical stability. Therefore, the sensor is applicable as a robust measurement tool in a wide field of industrial plasma processes. The ability of the probe to determine the electron density of the plasma as well as the collision frequency of the electrons is investigated by extensive 3D electromagnetic simulations. Measurements in a double inductively coupled plasma (DICP) reactor using different gas compositions with neutral gas temperatures exceeding 500° C confirm the suitability of the probe for a precise plasma monitoring at high temperatures. © 2018 IMA.
    view abstract10.23919/GEMIC.2018.8335073
  • Extraction of Relative Permittivity from Measured Reflection Coefficient of Dielectric Materials in the Frequency Range 207 - 247 GHz
    Alawnch, I. and Barowski, J. and Rolfes, I.
    2018 48th European Microwave Conference, EuMC 2018 (2018)
    This work describes the use of millimetre wave technology to extract the dielectric constants of different types of dielectric materials. The extraction of the dielectric materials is based on measurements (i.e., monostatic measurements) of the reflection coefficient for various dielectricmaterials. The measurements are done by utilizing a frequency modulated continuous wave radar with a dielectric lens antenna. The investigated materials are broadly utilized as a part of our everyday life. The fundamental dielectric materials outcomes are done for the following accompanying materials: Polytetrafluoroethylene (PTFE), mainly Teflon, nylon, and. The measurements are done in the frequency range from 207 GHz to 247 GHz. © 2018 European Microwave Association.
    view abstract10.23919/EuMC.2018.8541509
  • Hardware-accelerated embedded SAR processor for realtime FMCW radar applications
    Wagner, J. and Barowski, J. and Kalb, T. and Rolfes, I. and Göhringer, D.
    GeMiC 2018 - 2018 German Microwave Conference 2018-January (2018)
    A realtime Synthetic Aperture Radar (SAR) imaging system for Frequency Modulated Continuous Wave (FMCW) radars using hardware acceleration for highly efficient signal processing is presented. The backprojection algorithm is used for this purpose as it combines efficiency by using the Fast Fourier Transform (FFT) for range compression and the ability to process data after each measurement. A second radar sensor provides the possibility of a free motion during the measurement process. The signal processing is implemented on a Xilinx Zynq-7000 System on a Chip (SoC). It has a processor system as well as a programmable logic that can be used for hardware acceleration of suitable functions like the FFT and the backprojection algorithm. With this system design, up to 107 measurements per second can be processed. © 2018 IMA.
    view abstract10.23919/GEMIC.2018.8335080
  • Humanitarian Microwave Detection of Improvised Explosive Devices in Colombia
    Baer, C. and Schulz, C. and Just, T. and Gutierrez, S. and Orend, K. and Barowski, J. and Martinez, D. and Hattenhorst, B. and Jebramcik, J. and Pantoja, J. and Musch, T. and Rolfes, I. and Sachs, J. and Vega, F.
    Proceedings of the 2018 20th International Conference on Electromagnetics in Advanced Applications, ICEAA 2018 (2018)
    In this contribution, we present an overview and the latest research results regarding ground penetrating radar operation for humanitarian demining in Colombia. Next to the description of the investigated and manufactured radar equipment, we present a ground penetrating synthetic aperture radar (GPSAR) imaging approach. Moreover, the design of non-hazardous test scenarios and measurement results with the mentioned equipment are shown and discussed in detail. © 2018 IEEE.
    view abstract10.1109/ICEAA.2018.8520508
  • Investigation of fractal MIMO concepts for radar imaging of bulk solids
    Dahl, C. and Rolfes, I. and Vogt, M.
    European Microwave Week 2017: "A Prime Year for a Prime Event", EuMW 2017 - Conference Proceedings; 14th European Microwave Conference, EURAD 2017 2018-January (2018)
    In this contribution, fractal antenna array geometries for multiple-input multiple-output (MIMO) radar systems have been investigated for their applicability in surface measurements of bulk solids. Array geometries based on a diagonal array in combination with the quadratic flake fractal have been analyzed. The presented fractal MIMO concepts can be utilized in order to improve the angular resolution and to reduce the side lobe level, what is exemplarily shown for an antenna array with 25 transmit elements and 25 receive elements. With the proposed fractal MIMO concept, the angular resolution is improved to 4.1 degrees and the side lobe suppression is increased to 13.9 dB compared to MIMO configurations with a square virtual array and with the same number of elements. In addition, the results have been experimentally evaluated by radar measurements in a bunker silo scenario. © 2017 European Microwave Association.
    view abstract10.23919/EURAD.2017.8249165
  • Millimeter wave material characterization using FMCW-transceivers
    Barowski, J. and Rolfes, I.
    2017 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications, IMWS-AMP 2017 2018-January (2018)
    In this paper, ultra-wideband frecuency modulated continuous wave (FMCW) radar transceivers are used to measure the complex permittivity of dielectric materials. The radar transceivers are used to perform fast and accurate measurements from 200 GHz to 250 GHz within milliseconds. The dielectric constant and losses are determined using a free-space reflection measurement at normal incident on a given material sample. The FMCW transceiver is calibrated using adopted methods from vector network analysis. © 2017 IEEE.
    view abstract10.1109/IMWS-AMP.2017.8247432
  • Millimeter-wave characterization of dielectric materials using calibrated FMCW transceivers
    Barowski, J. and Zimmermanns, M. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 66 (2018)
    This paper presents a measurement setup, an extraction algorithm, and the results from material characterization measurements in the millimeter-wave (mm-wave) regime using ultrawideband frequency-modulated continuous-wave (FMCW) radar transceivers. The complex permittivity of dielectric and nonmagnetic materials is derived from radar echoes using a high-gain dielectric lens antenna setup and a measurement setup comprising elliptic mirrors. The radar transceivers perform fast and accurate measurements from 200 to 250 GHz within milliseconds. The FMCW transceivers are calibrated using a frequency-domain model that describes the systematic errors in the measurement setup. The characterization is done by a holistic model-based approach. Several well-known dielectric materials, such as polytetrafluorethylene, polyvinylchloride (PVC), or acrylic glass, are characterized among others to validate the setup's accuracy. The characterization is also done for different samples of polylactide, which is commonly used in additive manufacturing processes and 3-D printing, making it of high interest for the construction of mm-wave components. © 1963-2012 IEEE.
    view abstract10.1109/TMTT.2018.2854180
  • Progression of the Multipole Resonance Probe: Advanced Plasma Sensors Based on LTCC-Technology
    Pohle, D. and Schulz, C. and Oberberg, M. and Serwa, A. and Uhlig, P. and Awakowicz, P. and Rolfes, I.
    2018 48th European Microwave Conference, EuMC 2018 (2018)
    The multipole resonance probe (MRP) is a powerful and economical diagnostic tool for the determination of process-relevant plasma parameters. Due to its in-situ measurement concept even spatially resolved information of the plasma under investigation is provided. In order to minimize the influence of the sensor on the process, the planar multipole resonance probe (pMRP) was introduced as a minimally invasive monitoring tool, mounted into the reactor wall. For an effective application of these sensors in a wide field of real processes, industry compatible implementations are required. In this paper, advanced realizations of the MRP and pMRP based on LTCC-technology are presented, which are applicable for the supervision and control of plasma processes at high temperatures: the mathbf{MRP}-{mathbf{LTCC}} and the stacked mathbf{pMRP}-{mathbf{LTCC}}. The latter represents a novel compact design of the pMRP using an LTCC multilayer structure with vertically stacked components. Both sensors are investigated within 3D electromagnetic simulations and compared to measurements performed in a double inductively coupled plasma (DICP). © 2018 European Microwave Association.
    view abstract10.23919/EuMC.2018.8541730
  • Surface reconstruction using thinned random arrays in mm-wave FMCW SAR imaging
    Pohle, D. and Barowski, J. and Jebramcik, J. and Rolfes, I.
    European Microwave Week 2017: "A Prime Year for a Prime Event", EuMW 2017 - Conference Proceedings; 14th European Microwave Conference, EURAD 2017 2018-January (2018)
    In this paper the influence of a randomly thinned synthetic aperture on 3D surface reconstructions, utilizing a mm-wave radar at 240 GHz, is investigated. Using a uniformly sampled rectangular aperture of an adequate size, with regard to high cross-range resolutions, measurements can be very time consuming. This is due to the high operating frequencies, which make it necessary to shift the antenna in very small steps below one millimeter to fulfill the Nyquist sampling theorem. To overcome this problem, a non-uniform sampling approach using random measurement positions is suggested. Successively reducing the amount of positions in a random way causes noiselike artifacts, due to undersampling together with an overall degradation of the signal-to-noise ratio. In the following, the performance of the reconstruction under these conditions is examined in detail. © 2017 European Microwave Association.
    view abstract10.23919/EURAD.2017.8249207
  • A new calibration method for the measurement of a multiport microwave tomography system with a 2-port vector network analyzer
    Zimmermanns, M. and Rolfes, I. and Mallach, M. and Gebhardt, P. and Musch, T.
    European Microwave Week 2016: "Microwaves Everywhere", EuMW 2016 - Conference Proceedings; 46th European Microwave Conference, EuMC 2016 (2017)
    A new method for the calibration of a multiport microwave tomography (MWT) system measured with a 2-port vector network analyzer (VNA) is presented. The two VNA ports are mapped to the eight input ports of the MWT system by means of a switching network. This contribution deals with the calibration of the switching matrix. In consideration of the application, the proposed approach reduces the mechanical complexity of the calibration procedure significantly, by eliminating transmission connections between nonadjacent ports. This enables a simplified automation of the measurement setup. In addition, every step of the calibration procedure utilizes self-calibration techniques. Thereby, increasing the diversity of the procedure. Furthermore, the proposed method reduces the number of measurements required for the calibration in relation to comparable methods. © 2016 EuMA.
    view abstract10.1109/EuMC.2016.7824359
  • Characterizing Dielectric Materials using Monostatic Transmission-and Reflection-Ellipsometry
    Barowski, J. and Rolfes, I.
    Frequenz 71 (2017)
    The characterization of dielectric materials at microwave frequencies can be done by various measurement principles. Free space methods are a commonly used approach if the material under test (MUT) has to be characterized in-situ or in a non-destructive manner. Since the transmission and reflection parameters of a finite sized dielectric slab typically depend on its thickness, accurate knowledge about this parameter is of high importance. The ellipsometric approach presented in this paper eliminates the thickness dependence and thus allows to reduce a major source of error. This is achieved by performing four measurements. These measure the transmission and reflection factors of the MUT in both polarizations at an incident angle of 45°. The high stability of the measurement allows a simple monostatic setup utilizing a single antenna. The measurements in this paper are performed using Polytetrafluoroethylene (PTFE) and Polyvinylchloride (PVC) blocks in the frequency range from 22 GHz to 26 GHz. © 2017 by De Gruyter 2017.
    view abstract10.1515/freq-2016-0204
  • Collision frequency determination of low-pressure plasmas based on RF-reflectometry
    Schulz, C. and Rolfes, I. and Oberberg, M. and Awakowicz, P.
    European Microwave Week 2016: "Microwaves Everywhere", EuMW 2016 - Conference Proceedings; 46th European Microwave Conference, EuMC 2016 (2017)
    This paper introduces a robust collision frequency determination of low-pressure plasma processes. Based on the multipole resonance probe and in-situ reflection measurements, the input admittance of the system probe-plasma can be calculated. It can be used to determine the collision frequency via its width. The proposed evaluation is investigated by numerous parameter variations within 3D electromagnetic field simulations. For plasma electron frequencies, which can be determined simultaneously, over 4 GHz or collision frequencies below 200 MHz, a two-step compensation is necessary for reliable results. Based on the proposed compensation, a maximum error of ± 5% can be reached within the simulations. The final measurements in an argon-oxygen plasma confirm the suitability of the presented evaluation. © 2016 EuMA.
    view abstract10.1109/EuMC.2016.7824466
  • Dielectric phantom materials for broadband biomedical applications
    Hattenhorst, B. and Mallach, M. and Baer, C. and Musch, T. and Barowski, J. and Rolfes, I.
    2017 1st IEEE MTT-S International Microwave Bio Conference, IMBioC 2017 (2017)
    In this contribution, we present broadband microwave measurements on developed biomedical phantom materials. Therefore, we illustrate the reproducible mixing process of the realized phantom materials that are generated in different shapes with a potting compound and barium titanate. Moreover, three microwave measurement systems, including a coaxial probe, a microwave tomography system, and a radar ellipsometry system, characterize the dielectric behavior of the samples in different frequency bands. © 2017 IEEE.
    view abstract10.1109/IMBIOC.2017.7965802
  • Fractal antenna arrays for MIMO radar applications
    Dahl, C. and Vogt, M. and Rolfes, I.
    International Journal of Microwave and Wireless Technologies 9 (2017)
    In this contribution, fractal antenna arrays are analyzed for their applicability in multiple-input multiple-output (MIMO) radars. Array geometries based on the Fudgeflake fractal and the Gosper island fractal are investigated. In addition, a concept for the combination of both fractals is shown in order to increase the flexibility concerning the number of transmitting and receiving antennas. The presented fractal MIMO concepts can be utilized in order to improve the angular resolution and to reduce the sidelobe level for a given number of transmitting and receiving antennas. It is shown that a fractal MIMO concept with 21 transmitting antennas and 21 receiving antennas improves the angular resolution to 4.6 degrees and reduces side lobe level by 3.1 dB compared to a MIMO configuration based on two linear arrays with the same number of antenna elements. In addition, the results are experimentally validated by broadband radar measurements. Copyright © 2017 Cambridge University Press and the European Microwave Association.
    view abstract10.1017/S1759078717001015
  • Ground penetrating synthetic aperture radar imaging providing soil permittivity estimation
    Baer, C. and Gutierrez, S. and Jebramcik, J. and Barowski, J. and Vega, F. and Rolfes, I.
    IEEE MTT-S International Microwave Symposium Digest (2017)
    In this paper a combined Ground Penetrating Radar (GPR) and Synthetic Aperture Radar (SAR) technique is introduced, which considers the soil surface refraction and the wave propagation in the ground. By using Fermat's principle and the Sober operator, the SAR image of the GPR data is optimized, whereas the soil's permittivity is estimated. The theoretical approach is discussed thoroughly and measurements that were carried out on a test sand box verify the proposed technique. © 2017 IEEE.
    view abstract10.1109/MWSYM.2017.8058868
  • Microwave near-field sensor for the contactless detection of material fluctuations
    Hattenhorst, B. and Baer, C. and Musch, T. and Schulz, C. and Rolfes, I.
    European Microwave Week 2016: "Microwaves Everywhere", EuMW 2016 - Conference Proceedings; 46th European Microwave Conference, EuMC 2016 (2017)
    In this contribution a sensor concept for the contact-less detection of either dielectric or magnetic material fluctuations in its near-field is presented. The microwave sensor consists of two microstrip patch antennas connected to a reflectometer composed of a radio frequency (RF) measurement and a low frequency (LF) processing part. Due to the explicit, contactless detection of material variations, based on the detuning of antennas, the sensor is a versatile measurement instrument for the use in a wide field of applications. Measurements of single and compound components reveal the fully functional usage of the sensor. © 2016 EuMA.
    view abstract10.1109/EuMC.2016.7824392
  • On the usability of low-cost inertial navigation systems for free-hand SAR imaging at GPR-frequencies
    Baer, C. and Barowski, J. and Rolfes, I.
    SAS 2017 - 2017 IEEE Sensors Applications Symposium, Proceedings (2017)
    This contribution investigates the influence of Inertial Navigation System (INS) uncertainties for antenna positioning on Synthetic Aperture Radar (SAR) imaging. Therefore, a SAR simulator, which provides predefined positioning uncertainties is introduced. Two parameters of the resulting SARimage, i.e., the spatial resolution and the detection shift of a point target are investigated in range and azimuth direction. Moreover, a simple INS, which relies on an accelerometer, is introduced and the particular positioning method is discussed in detail. The applicability of the presented INS is investigated by means of SAR-measurements, which were performed with a Ground Penetrating Radar (GPR) antenna and a Vector Network Analyzer (VNA). Moreover, the resulting SAR images are evaluated by the defined properties and compared to SAR images, which rely on the same raw data, but utilize a positioning vector gathered by a high precision mmWave-radar. © 2017 IEEE.
    view abstract10.1109/SAS.2017.7894094
  • Plasma diagnostics in dielectric deposition processes
    Schulz, C. and Rolfes, I.
    Proceedings of IEEE Sensors (2017)
    This contribution presents an in-situ plasma probe, which is capable to measure precisely in the challenging environment of deposition processes. The probe is inserted into the plasma in order to determine critical parameters, which are required for a process control. Therefore, the effects of deposited dielectric materials, which adsorb onto the probe, are investigated within numerous pseudo deposition processes by 3D electromagnetic field simulations. Here, the adsorbed material is varied in its relative permittivity and layer thickness for two different loss tangents. The corresponding evaluations demonstrate the suitability and the prospects of the probe within these simulations. The final measurements in an argon-oxygen plasma, depositing TiO2, confirm the insensitivity of the probe. © 2016 IEEE.
    view abstract10.1109/ICSENS.2016.7808810
  • Real-time imaging system for millimeter wave synthetic aperture radar sensors
    Barowski, J. and Rolfes, I. and Baer, C.
    2017 1st IEEE MTT-S International Microwave Bio Conference, IMBioC 2017 (2017)
    In this contribution, a real-time imaging system alongside its processing chain for millimeter wave (mmWave) synthetic aperture radar (SAR) sensors operating at 240 GHz is presented. In addition to real-time capability, the SAR imaging system is manually moved on a linear track without precise stepper motors. Instead, the current position is obtained by a second radar measurement at a far lower frequency with an additional reference target. By this means, the image of the considered scene can be obtained in mere seconds. To allow real-time processing of the measurement data, a signal processing chain based on separate threads is established and further enhanced by using a graphics-processing unit (GPU). Due to the large imaging bandwidth of 50 GHz, the image system can be used to obtain high-resolution sub-surface images of e.g. construction materials. © 2017 IEEE.
    view abstract10.1109/IMBIOC.2017.7965769
  • A polarimetrie, low ringing UWB antenna for ground penetrating radar operation
    Baer, C. and Musch, T. and Schulz, C. and Rolfes, I.
    2016 IEEE Antennas and Propagation Society International Symposium, APSURSI 2016 - Proceedings (2016)
    In this contribution a dual-polarized (DP) UWB antenna for Ground Penetrating Radar (GPR) operation is introduced. Basing upon a Vivaldi structure, the proposed antenna provides high gain, low ringing and polarization purity. The low metal content, as well as the robust housing makes the antenna ideally suited for humanitarian demining field-operation. Measurement results concerning return loss, antenna pattern, and antenna ringing, which prove the antenna's applicability, are shown and discussed in detail. © 2016 IEEE.
    view abstract10.1109/APS.2016.7696767
  • Active contour extraction method for objects with a rough surface using single-chip FMCW radars
    Damyanov, D. and Friederich, B. and Schultze, T. and Willms, I. and Salman, R. and Barowski, J. and Rolfes, I.
    2016 IEEE Radar Conference, RadarConf 2016 (2016)
    In this paper a method for contour extraction of objects with a high degree of surface roughness in the range of 60 GHz Radar is presented. The proposed algorithm is based on an active contour model (snake) with external forces called component normalized gradient vector flow (CN-GVF). The snake algorithm extracts the contour of the object under test (OUT) based on wavefront Radar imaging methods. Experimental validations were performed with two fully integrated wideband frequency modulated continuous-wave (FMCW) single-chip Radar transceivers with an operational band from 57 GHz to 64 GHz, a corner cube retroreflector and a target object with a high degree of surface roughness. © 2016 IEEE.
    view abstract10.1109/RADAR.2016.7485228
  • An electronically reconfigurable reflectarray element based on binary phase shifters for K-band applications
    Theissen, H. and Dahl, C. and Rolfes, I. and Musch, T.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    A reflectarray concept which allows electronic beam-steering by using a binary phase approximation is presented. The proposed antenna element works at 24 GHz and is comprised of an aperture-coupled patch antenna with an open-ended microstrip line on the backside to obtain the proper phase distribution on the reflectarray aperture. Electronic beam-steering is achieved by applying PIN diodes on the individual reflectarray elements. To simplify the control process of the antenna, the elements function as one-bit phase shifters either reflecting with a 0° or 180° phase shift. The reflectarray element is verified by measurements obtained with a prototype in a waveguide simulator setup. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461621
  • Analysis of composite materials with periodically aligned inclusions using 3D em field simulations
    Baer, C. and Hattenhorst, B. and Schulz, C. and Will, B. and Rolfes, I. and Musch, T.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    In this contribution, the effective permittivity of material compositions with special focus on the influence of periodically aligned inclusions is investigated. Therefore, several electromagnetic simulations on the material under test (MUT), which consists of a homogeneous host material and numerous spherical inclusions, are performed. By means of a rectangular waveguide setup, FDTD-simulations, and accurate permittivity determination algorithms, the MUT's effective, complex permittivity is investigated over a broad frequency range. Moreover, the results of materials with periodically aligned inclusions are compared to materials with fully randomized inclusions that exhibit equal material parameters. Detailed information on the investigation procedure as well as comparisons to theoretical permittivity values, calculated by common mixing equations, are presented and discussed. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461571
  • Diagnostics of plasma processes based on parallelized spatially resolved in-situ reflection measurements
    Schulz, C. and Runkel, J. and Oberberg, M. and Awakowicz, P. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 64 (2016)
    A parallelized in-situ plasma measurement setup, consisting of two multipole resonance probes (MRP), a passive signal divider, and two coaxial cables with different lengths is presented in this contribution. The combined reflection coefficient of the applied probes is measured, separated in the time domain, and evaluated. Here, each MRP is able to measure the spatially resolved plasma electron density via its resonance behavior precisely and quasi-simultaneously. Furthermore, the return loss (RL) changes with the collision frequency, which can be detected for each probe. The parallelization and the applied signal processing are confirmed by simulations and combined measurements in CST Schematic as well as by in-situ measurements in an argon plasma. The resulting error is below 1% for the resonance frequency and below 8% for the corresponding RL. Hence, the input power and gas pressure of a plasma process can be controlled effectively. © 2015 IEEE.
    view abstract10.1109/TMTT.2015.2510653
  • Monitoring of low pressure plasmas with a calibrated probe
    Runkel, J. and Schulz, C. and Rolfes, I. and Oberberg, M. and Awakowicz, P.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    In this contribution the use of the planar multipole resonance probe (pMRP) as a monitoring tool for low pressure plasmas is presented. By 3D electromagnetic simulations, the probe's ability to monitor two important plasma parameters is investigated and a full one-port calibration is applied to ensure maximum monitoring precision. Measurements in a double inductively coupled argon plasma confirm the simulation results and prove the suitability of the calibrated pMRP for precise plasma monitoring. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461551
  • Monostatic and thickness-independent material characterisation based on microwave ellipsometry
    Barowski, J. and Schultze, T. and Willms, I. and Rolfes, I.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    Material characterization utilizing microwave ellipsometry is based on the fact that the reflection coefficients of a wave impinging on a material depend on the incident fields polarization. Due to multiple reflections that occur in case of a material slab with finite dimensions these coefficients also strongly depend on the materials thickness. This paper describes an approach to determine the electromagnetic properties of a material under test by applying an ellipsometric measurement without knowledge of the materials thickness. The paper shows that the additional measurement of the transmission coefficients allows to perform an exact measurement of the complex permittivity since the thickness dependencies in reflection and transmission coefficients are removed. The measurements are done in the frequency range from 22 GHz to 26 GHz by using a vector network analyzer setup with a conical horn antenna. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461652
  • Multi-spectral echo signal processing for improved detection and classification of radar targets
    Vogt, M. and Neumann, T. and Gerding, M. and Dahl, C. and Rolfes, I.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    A major challenge in radar based remote sensing and imaging is to identify and to detect radar targets, and also to accurately determine their locations and sizes. This especially applies in the case of multiple, spatially distributed radar targets, as for example in radar imaging, automotive radars, and others. Previously, we have proposed a concept for multi-spectral analysis and processing of echo signals for radar level measurement of bulk solids in silos using a spatially fixed antenna beam. This approach has now also been utilized for scanning radar applications. The basic technique is to filter the radar echo signals in multiple frequency sub-bands and to incoherently combine the filtered signals. Furthermore, the variance of envelope signals is analyzed in order to allow for a differentiation between echoes from distributed, randomly arranged scatterers and from spatially isolated single scatterers. The mean over the standard deviation of the envelope signals obtained from the different sub-bands is suggested to be used as an amplitude-invariant parameter for the classification of radar targets. Results of an experimental evaluation of the concept using a mechanically scanning 75 to 80 GHz Frequency Modulated Continuous Wave (FMCW) radar system are presented. It will be shown that the proposed technique enables to largely suppress the echo signal fluctuations, which are given in scenarios of spatially distributed radar targets, and also to distinguish between different kinds of radar targets. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461618
  • Multiport calibration for microwave tomography systems
    Zimmermanns, M. and Rolfes, I. and Mallach, M. and Gebhardt, P. and Musch, T.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    A method for the calibration of an ultra-wideband microwave tomography system is presented. The objective for this measurement system is to calculate the spatial distribution of the dielectric parameters and thereby different materials. Scattering parameters are used to describe the setup and are given to the reconstruction algorithm for evaluation. The measured wave parameters of this system are influenced by the measurement instrument as well as by the setup itself. In addition, it is also necessary for the reconstruction to obtain the scattering parameters at a well defined reference plane. Both requirements can be achieved by the help of a multiport error correction algorithm used for the calibration of a Vector Network Analyzer (VNA). In a first step, an error model for the tomographic system is presented. Secondly, this paper provides a concept for calibration standards which can be used for this application. Since a tomographic system do not offer the possibility for the use of classic reflection standards or a change in the mechanical length of the transmission other calibration standards have to be found. The idea of a homogeneous filling of the tomograph is presented. With the help of a simulation model the requirements for the system as well as the accuracy of the results are analyzed. In addition, measurement results are shown to validate the proposed approach. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461565
  • A two-dimensional radar simulator for level measurement of bulk material in silos
    Dahl, C. and Rolfes, I. and Vogt, M.
    2015 German Microwave Conference, GeMiC 2015 (2015)
    In this contribution, a two-dimensional radar simulator, which is used to determine the specifications and to predict the accuracy of a scanning radar system for filling volume measurement of bulk solids in silos, is presented. The simulator is based on a simple scattering model using polar coordinates in order to achieve an efficient implementation. Additionally, a detection algorithm based on a speckle filter has been tested for an exemplarily bulk solid scenario, and the influence of the penetration depth of the bulk solid, the antenna beam width, and the filling level on the measurement error has been analyzed. With a minimum signal to noise ratio of 10 dB, a measurement error smaller 2 m has been obtained for the given scenario. © 2015 IMA: IMATech e.V.
    view abstract10.1109/GEMIC.2015.7107793
  • An 80 GHz radar level measurement system with dielectric lens antenna
    Vogt, M. and Schulz, C. and Dahl, C. and Rolfes, I. and Gerding, M.
    Proceedings International Radar Symposium 2015-August (2015)
    In this contribution, a Frequency Modulated Continuous Wave (FMCW) radar system, working in the 75 to 85 GHz frequency range, for level measurement of liquids in tanks is presented. The realized radar antenna has been specially designed to cope with the given harsh environmental conditions (high pressure, high temperature, explosion protection requirements, etc.) in industrial applications. The basic design concept of the antenna is to utilize a dielectric lens as 'barrier element' between the tank and the radar electronics module, and especially for high-pressure applications, a cylindrical glass element is included into the lens system. Different configurations of dielectric lens antennas (different biconvex and plano-convex lenses with 45 mm diameter), also in versions including a glass barrier element with 20 mm thickness, have been evaluated by means of electromagnetic field simulations and measurements. A circular waveguide with 2.6 mm inner diameter equipped with a conical horn with 4.8 mm diameter and 3 mm length is used as feeding structure. Results demonstrate a range pulse width (-6 dB) of 30 mm with the full bandwidth of 10 GHz of the system. As expected, the best antenna performance is given with the biconvex lens antenna without the glass barrier element. Nevertheless, a reasonably good performance in the case of equipping the glass barrier with plano-convex dielectric lenses at its front and rear sides can be achieved. © 2015 German Institute of Navigation (DGON).
    view abstract10.1109/IRS.2015.7226222
  • Characterizing surface profiles utilizing mm-wave FMCW SAR imaging
    Barowski, J. and Pohle, D. and Jaeschke, T. and Pohl, N. and Rolfes, I.
    European Microwave Week 2015: "Freedom Through Microwaves", EuMW 2015 - Conference Proceedings; 2015 45th European Microwave Conference Proceedings, EuMC (2015)
    In this paper the results from characterizing complex surface profiles with a synthetic aperture radar operating at frequencies up to approx. 250 GHz are presented. The radar uses a bandwidth of 38GHz and a maximum synthetic aperture of 40 cm times 40 cm and is thus rectangular and uniformly sampled. A fast parallel backprojection algorithm that can be used with general purpose GPUs is used for image reconstruction. The performance of the measurement system is evaluated with respect to the range-and cross-range-resolution as well as the overall measurement error on a given reference surface. Also the measurement performance on sharp edges is considered. © 2015 EuMA.
    view abstract10.1109/EuMC.2015.7345796
  • Comparison of virtual arrays for MIMO radar applications based on hexagonal configurations
    Dahl, C. and Rolfes, I. and Vogt, M.
    2015 European Radar Conference, EuRAD 2015 - Proceedings (2015)
    In this contribution a MIMO radar concept based on a hexagonal configuration of antenna elements is presented. The concept has been designed for a radar system with 7 transmitting and 7 receiving antenna elements and has been compared to a common two dimensional MIMO arrangement. It is shown that the presented hexagonal setup improves the side lobe suppression by 3 dB while enhancing the angular resolution to 13.8°. Furthermore a thinning method for the hexagonal arrangement is presented. Finally, radar measurements have been performed in order to compare the performance of the concepts in a close range scenario. © 2015 EuMA.
    view abstract10.1109/EuRAD.2015.7346326
  • Conformal mm-wave antennas for catheter embedded atherosclerotic plaque sensors
    Notzon, G. and Baer, C. and Musch, T. and Dahl, C. and Rolfes, I.
    European Microwave Week 2015: "Freedom Through Microwaves", EuMW 2015 - Conference Proceedings; 2015 45th European Microwave Conference Proceedings, EuMC (2015)
    This contribution shows a sensor design for the intravascular differentiation of vulnerable and calcified plaques. A measurement concept based on the reflection of an oblique incident electromagnetic wave at the dielectric interface between blood and plaque is discussed. Therefore, the indispensable dielectric properties of both materials are presented. For a catheter embedded solution the sensor is optimized with respect of small geometries and a smooth cylindrical shape. The optimization and verification are performed by means of 3D electromagnetic wave simulations. Furthermore, a broadband measurement concept is presented, which provides additional information for the plaque type differentiation. © 2015 EuMA.
    view abstract10.1109/EuMC.2015.7345891
  • Development and analysis of a modified Saleh-Valenzuela channel model for the UHF band
    Nalobin, A. and Dortmund, S. and Sczyslo, S. and Barowski, J. and Meiners, B. and Rolfes, I.
    2015 German Microwave Conference, GeMiC 2015 (2015)
    This contribution deals with the analysis of a modified Saleh-Valenzuela channel model for the UHF band. The development of the channel model is based on indoor channel measurements within a large exhibition hall in a line-of-sight scenario in order to study new cognitive radio systems. Contrary to the conventional modeling, the path voltage gain is modeled by a Rayleigh probability density function. Due to the broad-band consideration the channel model can be used for a variety of different operating frequencies. © 2015 IMA: IMATech e.V.
    view abstract10.1109/GEMIC.2015.7107748
  • Dielectric waveguides for industrial radar applications
    Baer, C. and Schulz, C. and Rolfes, I. and Musch, T.
    International Journal of Microwave and Wireless Technologies 7 (2015)
    In this paper, we present several dielectric waveguide (DWG) setups that enable the transition between radar front ends and antennas in challenging, industrial environments. Apart from good propagation behavior, DWG provide a nearly dispersion free transmission over large distances. Furthermore, they can be used as an electrical insulator in places with critical creep distances, in high temperature environments, and for applications with limited installation space. Fundamentals concerning the ideal propagation mode and adequate waveguide-fiber transitions are presented. Results of electromagnetic simulations as well as measurements on manufactured DWG are discussed in detail. The presented excellent propagation behavior proves the effectiveness of the proposed setup. Copyright © Cambridge University Press and the European Microwave Association 2015.
    view abstract10.1017/S1759078715000136
  • Effective permittivity determination of randomized mixed materials using 3D electromagnetic simulations
    Baer, C. and Hattenhorst, B. and Schulz, C. and Will, B. and Rolfes, I. and Musch, T.
    2015 IEEE MTT-S International Microwave Symposium, IMS 2015 (2015)
    In this contribution, we present a novel simulation based technique for the investigation of arbitrary dielectric material compositions. The proposed procedure bases on a randomization process in combination with transient 3D electromagnetic simulations and robust signal processing. The comparison to commonly known dielectric mixing rules proves the effectiveness of the automated simulation process. Detailed information on the randomized material modeling, the simulation process as well as the evaluation of the applicability of the proposed method are part of this contribution. © 2015 IEEE.
    view abstract10.1109/MWSYM.2015.7166797
  • Electromagnetic characterization of fluid vortices by means of three-dimensional field simulations
    Hattenhorst, B. and Baer, C. and Musch, T. and Schulz, C. and Rolfes, I.
    European Microwave Week 2015: "Freedom Through Microwaves", EuMW 2015 - Conference Proceedings; 2015 45th European Microwave Conference Proceedings, EuMC (2015)
    In this contribution a simulation concept of fluid vortices in three-dimensional electromagnetic field simulators is presented. Two-dimensional models are shown that describe pressure distributions of vortices. By inserting these into dielectric mixing equations, a new dielectric distribution of a vortex is obtained. Converting the two-dimensional permittivity distribution in a three-dimensional model enables examinations in electromagnetic field simulators that identify fundamental dependencies of a propagating electromagnetic wave and a fluid vortex. © 2015 EuMA.
    view abstract10.1109/EuMC.2015.7345692
  • Electron density determination for plasma assisted sterilization processes
    Schulz, C. and Runkel, J. and Rolfes, I.
    2015 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2015 - Proceedings (2015)
    An effective measurement concept for the precise determination of the electron density in plasma assisted sterilization processes is presented in this paper. Here, plasmas offer a promising approach for heat or chemical sensitive materials, like surgery instruments. Therefore, the Multipole Resonance Probe (MRP) is investigated over a wide frequency range. Based on the evaluation of an unambiguous resonance behaviour, the resonance frequency can be determined from 0.5 to 6 GHz. Proven in 3D electromagnetic field simulations and measurements in an excited Argon plasma, the additional center of gravity method increases the performance and the MRP can be used for an evaluation of a wide density range. Hence, the density can be controlled effectively and used in a feedback control loop. © 2015 IEEE.
    view abstract10.1109/IMWS-BIO.2015.7303803
  • Investigation of a circular TE11-TE01-mode converter in stepped waveguide technique
    Schulz, C. and Baer, C. and Musch, T. and Rolfes, I. and Will, B.
    International Journal of Microwave and Wireless Technologies 7 (2015)
    A compact and broadband TE11-TE01-mode converter, suitable for various industrial applications like bypass level measurements, is presented in this contribution. Based on stepped waveguide technique, the main advantages of the recommended converter design and the specific field distribution of the TE01-mode are discussed in detail. The converter is presented exemplary for a frequency range from 23 to 28 GHz, which corresponds to a bandwidth of approximately 20 % of the center frequency. Numerous three-dimensional electromagnetic field simulations are performed to optimize the converter and to investigate its reflection and transmission behavior. Realized by six different single elements and 11 parts in total, fast and effective simulations can be performed with CST Microwave Studio. Considering realistic production process parameters, like fillets or tolerances, a good return loss better 17 dB, an insertion loss of 0.1 dB, and an excellent mode purity are achieved. Compared with back-to-back, realistic disturber scenario, and far-field measurements with a first prototype, the expected excellent converter behavior can be validated without limitations. Hence, the suitability of the presented converter design is proven and the feasibility is demonstrated. Copyright © Cambridge University Press and the European Microwave Association 2015.
    view abstract10.1017/S1759078715000203
  • Microwave sensor concept for the detection of gas inclusions inside microfluidic channels
    Hattenhorst, B. and Theissen, H. and Schulz, C. and Rolfes, I. and Baer, C. and Musch, T.
    2015 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2015 - Proceedings (2015)
    In this contribution a new sensor concept for the detection of gas inclusions in microfluidic channels is presented. The sensor operates at microwave frequencies with two microstrip patch antennas. To prevent gas embolism in a variety of clinical branches the sensor yields a powerful detection since patch antennas operate at different frequencies for different permittivities surrounding them. Simulations and measurements reveal that monitoring of the shifting resonance frequency indicates changing materials like gas in liquids. © 2015 IEEE.
    view abstract10.1109/IMWS-BIO.2015.7303801
  • On the human blood permittivity: Model parameters and substitution material for mmWave applications
    Baer, C. and Schulz, C. and Notzon, G. and Rolfes, I. and Musch, T.
    2015 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2015 - Proceedings (2015)
    In this contribution, we present latest measurement results on human blood permittivity within the frequency range from 10GHz to 40GHz. Because bio sensor testing inside of real human blood is often critical, we propose a substitution material that is nonhazardous and unperishable. Furthermore, corresponding parameters for the advanced Cole-Cole model are presented for all investigated materials. © 2015 IEEE.
    view abstract10.1109/IMWS-BIO.2015.7303760
  • Parallelization concept for spatially resolved in-situ plasma measurements
    Schulz, C. and Runkel, J. and Rolfes, I.
    2015 IEEE MTT-S International Microwave Symposium, IMS 2015 (2015)
    A novel, simple, and passive parallelization concept for the simultaneous determination of plasma density by spatially resolved plasma probes is presented in this paper. Based on the so-called Multipole Resonance Probe (MRP), a Wilkinson divider, and two coaxial cables with different length, the resulting reflection coefficients of each probe can be separated in time domain. Hence, the corresponding plasma density at different positions in a reactor can be determined without limitations. The basic concept is confirmed by simulative investigations in CST Schematic. Therefore, 3D electromagnetic simulations are combined with numerical models and the signal processing is both, investigated and evaluated. Compared to a measurement based setup, an excellent agreement is achieved and the concept is proven. © 2015 IEEE.
    view abstract10.1109/MWSYM.2015.7167113
  • The Planar Multipole Resonance Probe: Challenges and Prospects of a Planar Plasma Sensor
    Schulz, C. and Styrnoll, T. and Awakowicz, P. and Rolfes, I.
    IEEE Transactions on Instrumentation and Measurement 64 (2015)
    A novel compact plasma sensor applicable for the supervision and control of industrial plasma processes is presented in this contribution. Based on the multipole resonance probe (MRP), the new planar MRP (pMRP) is introduced as a powerful and economical monitoring tool, flush-mounted into the reactor wall. Hence, it can be used for an effective suppression of disturbances of the plasma process itself. Using 3D electromagnetic field simulations with CST Microwave Studio, the pMRP is investigated and challenges as well as prospects of the new sensor design are discussed in detail. Three different sensor versions are presented and compared with the resonance behavior of the MRP. Furthermore, limitations concerning position tolerances are shown and the suitability of the pMRP is proven. Measurements in a double inductive coupled plasma, with argon as process gas and varying excitation powers, demonstrate the suitability of the pMRP for monitoring purposes. © 1963-2012 IEEE.
    view abstract10.1109/TIM.2014.2358111
  • Utilization of the array factor for narrowband direction of arrival estimation
    Nalobin, A. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 2015-October (2015)
    This contribution deals with the direction of arrival estimation of narrowband signals using an antenna array. Under sparsity constraints the estimation procedure is based on compressed sensing by altering the array factor of the antenna. This approach allows to influence directly the incoherence requirement of the sensing matrix. Simulation results are provided to present the performance of the proposed method. © 2015 IEEE.
    view abstract10.1109/APS.2015.7304588
  • A broadband circular TE11- to TE01-mode converter using stepped waveguide technique
    Schulz, C. and Rolfes, I. and Will, B.
    European Microwave Week 2014: Connecting the Future, EuMW 2014 - Conference Proceedings; EuMC 2014: 44th European Microwave Conference (2014)
    This paper introduces a broadband and compact circular TE<inf>11</inf>- to TE<inf>01</inf>-mode converter, realized in stepped waveguide technique and therefore easy to manufacture with standard mortising machines. The concept is presented exemplary for a conversion in a frequency range from 23 GHz to 28 GHz. Hence, a bandwidth of approximately 20 % of the center frequency can be achieved. For the development of an optimized converter design, 3D electromagnetic field simulations are performed within CST Microwave Studio 2013. The simulations include realistic production process parameters, like fillets or tolerances, and show a good return loss of at least 17 dB, while the insertion loss is below 0.1 dB. Compared to measurements of a first prototype in back-to-back assembly, the measurement results validate the expected excellent converter behaviour. Hence, the suitability of the presented converter design is proven and the feasibility is demonstrated. © 2014 European Microwave Association.
    view abstract10.1109/EuMC.2014.6986432
  • A miniaturized soil moisture sensor based on time domain transmissometry
    Will, B. and Rolfes, I.
    2014 IEEE Sensors Applications Symposium, SAS 2014 - Proceedings (2014)
    Delay time measurements are a powerful method for soil moisture measurements. Besides the well-known time domain reflectometry (TDR), a new method, namely the time domain transmissometry (TDT) captures the market for soil moisture sensors. The key benefit of transmission measurements is their robustness against multiple reflections. However, the development of TDT sensors for measurements inside soils is a challenge due to specific geometric requirements. While transmission measurements are in general performed in two port setups, measurements inside soils require an one port setup. Hence, time domain sensors are in general based on reflection measurements. This contribution describes a soil moisture sensor, which combines the advantages of TDR and TDT measurements regarding the suitability for soil moisture measurements. The sensor consists of a concentric coaxial line assembly resulting in a compact setup. The measuring path is realized as an one-wire line to obtain a large cross sectional area and thus, a large soil sample volume. © 2014 IEEE.
    view abstract10.1109/SAS.2014.6798952
  • A new approach on advanced compact plasma sensors for industrial plasma applications
    Schulz, C. and Rolfes, I.
    2014 IEEE Sensors Applications Symposium, SAS 2014 - Proceedings (2014)
    A novel compact plasma sensor applicable for the supervision and control of industrial plasma processes is presented in this contribution. Based on the multipole resonance probe (MRP), the new planar multipole resonance probe (pMRP) flush-mounted into the reactor wall can be used for an effective suppression of disruptions on the plasma process itself. Using 3D-electromagnetic field simulations, the MRP and the pMRP are investigated and compared. Furthermore, limitations concerning position tolerances are shown and the suitability is demonstrated. © 2014 IEEE.
    view abstract10.1109/SAS.2014.6798958
  • A robust dielectric feeding concept for harsh environmental TLPR antennas
    Baer, C. and Musch, T. and Schulz, C. and Rolfes, I.
    European Microwave Week 2014: "Connecting the Future", EuMW 2014 - Conference Proceedings; EuRAD 2014: 11th European Radar Conference (2014)
    In this contribution a novel dielectric waveguide setup is introduced that enables the transition between radar front ends and antennas in harsh environments. Apart from the good propagation behavior it provides a nearly dispersion free transmission over large distances. Furthermore, it can be used as an electrical insulator in places with critical creep distances. Fundamentals concerning the ideal propagation mode and adequate waveguide-fiber transitions are presented. Results of electromagnetic simulations as well as measurements on a manufactured dielectric waveguide are discussed in detail. The presented excellent propagation behavior proves the effectiveness of the proposed setup. © 2014 EuMA.
    view abstract10.1109/EuRAD.2014.6991266
  • A stacked sensor concept for industry compatible plasma diagnostics
    Schulz, C. and Will, B. and Rolfes, I.
    Proceedings - 2014 International Conference on Electromagnetics in Advanced Applications, ICEAA 2014 (2014)
    This paper presents a stacked sensor concept, which is producible entirely on standard printed circuit boards and applicable for the control of industrial plasma processes. Starting with the so-called multipole resonance probe (MRP) the prospects and the development towards the stacked MRP (sMRP) are discussed. The conversion of the MRP into a discretized spherical setup, using printed half discs of varying radii, is investigated. 3D electromagnetic field simulations yield an optimized assembly of 25 PCBs for a replication of the probe head. Measurements of a first prototype in a double inductive coupled plasma with an excited argon-hydrogen plasma have proven the expected resonance behaviour. In comparison to the MRP and the simulations, the applicability of the stacked sensor concept is demonstrated. © 2014 IEEE.
    view abstract10.1109/ICEAA.2014.6903945
  • A system simulator including channel and frontend models for cognitive professional wireless microphones
    Barowski, J. and Meiners, B. and Nalobin, A. and Dortmund, S. and Sczyslo, S. and Rolfes, I.
    2014 1st International Workshop on Cognitive Cellular Systems, CCS 2014 (2014)
    In this paper a simulation environment for indoor transmissions in the ultra high frequency band is presented. The simulator comprises hardware as well as channel models that were derived from extensive measurement campaigns. In case of hardware modeling, nonlinear memory-polynomial models are used in order to accurately describe the intermodulation between multiple receive signals. The presented channel model is structured into three layers for indoor line of sight, non line of sight as well as outdoor to indoor transmissions. The indoor models utilize a Saleh-Valenzuela approach and a Clarke's model, while the outdoor model makes use of a Hata model. © 2014 IEEE.
    view abstract10.1109/CCS.2014.6933786
  • Dielectric tube antennas for industrial radar level gauging
    Armbrecht, G. and Zietz, C. and Denicke, E. and Rolfes, I.
    IEEE Transactions on Antennas and Propagation 60 (2014)
    This paper concerns dielectric tube antenna design in the frequency range from 8.5 to 10.5 GHz for the use in the field of industrial radar level gauging for process automation industry. The application is based on monostatic radar configurations, which thus demands for highly directive endfire antennas made of chemically inert dielectrics, such as polytetrafluoroethylene (PTFE) or polypropylene (PP). Herein, the antennas consist of solid and tubular waveguides with cylindrical cross sections as well as transitions among these sections. In order to approach the promising theoretical directivity limits of thin-walled dielectric tubes at small aperture diameters, a fundamental HE11 mode-preserving waveguide transition forms the core element of the antenna. This yields compact dielectric antennas with directivity levels of around 20 dBi. By this means, a significant improvement in comparison to a circular metallic horn aperture of the same outer diameter as the radiating tube and a length reduction with regard to dielectric rod antennas is achieved. Finally, prototypes of the proposed antennas are manufactured and verified by measurements. © 2012 IEEE.
    view abstract10.1109/TAP.2012.2207693
  • Narrow-band indoor localization in cognitive radio networks using compressed sensing
    Nalobin, A. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2014)
    This contribution deals with narrow-band target localization in cognitive radio networks. In particular the localization is of interest to narrow-band programme making and special event applications in indoor scenarios. The procedure to find the location is based on a compressed sensing approach, which allows the solution of underdetermined systems of linear equations. The algorithm uses the received signal strength, which was derived by ray tracing techniques applied to a 3D model of the fairground of Berlin. The accuracy of the proposed procedure is analytically studied through simulations. © 2014 IEEE.
    view abstract10.1109/APS.2014.6904910
  • Narrowband direction-of-arrival estimation of near-field sources using compressed sensing
    Nalobin, A. and Rolfes, I.
    European Microwave Week 2014: Connecting the Future, EuMW 2014 - Conference Proceedings; EuMC 2014: 44th European Microwave Conference (2014)
    This contribution deals with the direction-of-arrival estimation of narrowband signals in near-field scenarios using compressed sensing strategies. The considerations relate to a single snapshot of the signal impinging on a sensor array. For the estimation a near-field formulation of the array manifold vector is used. This approach also allows to draw conclusion on the distance between the array and the sources. Simulation as well as measurement results are provided to present the performance of the proposed method. © 2014 European Microwave Association.
    view abstract10.1109/EuMC.2014.6986371
  • The multipole resonance probe: Progression and evaluation of a process compatible plasma sensor
    Schulz, C. and Styrnoll, T. and Storch, R. and Awakowicz, P. and Musch, T. and Rolfes, I.
    IEEE Sensors Journal 14 (2014)
    A robust and sensitive plasma sensor, the multipole resonance probe (MRP), and its process compatibility are presented and discussed in this paper. Based on its innovative concept and simple model describing the system 'probe-plasma', three steps of development are introduced. 3D electromagnetic field simulations are applied as an indispensable tool for an economical and efficient investigation and optimization of different sensor layouts. Independent of the chosen sensor design, a developed pulse-based measurement device yields an economical signal generation and evaluation. Electron density profiles, determined with the MRP and the pulse-based system utilized in a capacitive coupled plasma, confirm and demonstrate the simulation results and the measurement concept, respectively. © 2014 IEEE.
    view abstract10.1109/JSEN.2014.2333659
  • A millimeter-wave based measuring method for the differentiation of atherosclerotic plaques
    Baer, C. and Notzon, G. and Dahl, C. and Schulz, C. and Will, B. and Rolfes, I. and Musch, T.
    2013 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2013 - Proceedings (2013)
    In this contribution, a novel measuring method for the differentiation of intra vascular plaque types is presented. The proposed method operates contact free because of the mm-wave based approach. Fundamentals concerning material properties of blood and plaque, and electromagnetic barrier reflections are discussed. Furthermore, a test setup consisting of a miniaturized sensor setup is introduced that clarifies the measuring concept. Additionally, results of 3D electromagnetic field simulations as well as first measurements ex situ performed on non-human genetic materials are shown and discussed in detail. © 2013 IEEE.
    view abstract10.1109/IMWS-BIO.2013.6756167
  • A monostatic antenna-reflector system for ultra-short-range radar applications
    Baer, C. and Musch, T. and Schulz, C. and Will, B. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2013)
    In this contribution, a novel antenna-reflector system is introduced, which consists of a planar waveguide orthomode transducer, a lens-horn antenna and a transpolarizing reflector. The proposed antenna system eliminates short-range clutter effects like root point reflections and antenna ringing effectively. The setup enables ultra-short-range radar measurements as they are used e.g. for material characterization measurements. Results of 3D-electromagnetic field simulations as well as measurements, that prove the effectiveness of the antenna setup are shown and discussed in detail. © 2013 IEEE.
    view abstract10.1109/APS.2013.6711137
  • A multi directional dielectric lens approach for antennas used in industrial RADAR applications
    Schulz, C. and Baer, C. and Pohl, N. and Musch, T. and Will, B. and Rolfes, I.
    2013 International Workshop on Antenna Technology, iWAT 2013 (2013)
    A multi directional dielectric lens approach for beam steering on the basis of an ellipsoidal antenna is presented in this paper. Good antenna characteristics allow a modification of the feeding device used for the desired beam steering in industrial RADAR applications at 24 GHz. Based on a geometrical-optical lens approach and 3D-electromagnetic field simulations the antenna is investigated and the resulting effects of the modification are discussed. The antenna beam is steerable in a wide range, only limited by the antenna dimensions. Using a movable waveguide or multiple feeding elements in one antenna within the same plane, an adjustable beam direction as well as a multistatic beam steering can be realized. Measurements of a prototype confirm the expected behaviour and demonstrate the applicability of the dielectric ellipsoidal lens antenna for beam steering in industrial RADAR applications. © 2013 IEEE.
    view abstract10.1109/IWAT.2013.6518358
  • A synthetic calibration technique for broadband applications using focusing antenna setups
    Will, B. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2013)
    This contribution describes a new calibration procedure, which is advantageous for broadband free space setups. This method is based on well-known self calibration techniques like thru-reflect-line (TRL). In contrast to the commonly used mechanical line standard the proposed procedure makes use of a synthetic line standard, which is realized by using different frequency points. Thus, the necessary shift of the electrical length is achieved by a shift of frequency instead of a shift of mechanical length. Hence, the synthetic calibration technique does not require any mechanical displacements of the setup. In addition, the number of measurements is reduced, since a separate measurement of the line standard is not required. This approach is verified by measurements and compared with conventional TRL calibration techniques. © 2013 IEEE.
    view abstract10.1109/APS.2013.6711020
  • Compact unfocused antenna setup for X-band free-space dielectric measurements based on line-network-network calibration method
    Orlob, C. and Reinecke, T. and Denicke, E. and Geck, B. and Rolfes, I.
    IEEE Transactions on Instrumentation and Measurement 62 (2013)
    This paper presents a compact free-space measurement system for the characterization of dielectric materials within the X-band based on the line-network-network (LNN) calibration method. Using a pair of dielectric-filled horn antennas with enhanced directivity, the setup exhibits a total length of 250 mm between the antenna apertures and is suitable for measurements of planar samples with transverse dimensions equal to or greater than 250 mm × 250 mm. Based on 3-D field simulations and measurements, the assumptions of plane wave incidence on the sample and negligible diffraction effects at the sample edges are investigated. The scattering parameters of the sample are obtained according to the LNN calibration method. Remaining multipath propagation effects caused by reflections at the antennas and their fixtures are filtered out via time gating. The complex permittivity is finally calculated from the transmission scattering parameter using the Newton-Raphson method. Results for exemplary dielectrics are in good accordance with reference values. © 1963-2012 IEEE.
    view abstract10.1109/TIM.2013.2246905
  • Comparative study of moisture measurements by time domain transmissometry
    Will, B. and Rolfes, I.
    Proceedings of IEEE Sensors (2013)
    Time domain transmissometry (TDT) is an emerging technology in the field of moisture measurements. While time domain reflectometry (TDR) is a well-known method for moisture measurements since the 1980s, TDT measurements were not applied until the last decade. The key benefit of TDT measurements is the robustness against multiple reflections along the sensor resulting in higher measurement accuracy and lower requirements concerning the electronics. However, transmission measurements in soil, grain, or other bulky goods yield some difficulties. Especially the realization of a second measuring port at the end of the sensor is challenging. This contribution gives an overview on TDT systems for moisture measurements. Beside the theoretical background, existing sensors and measurement systems are compared and illustrated in detail. © 2013 IEEE.
    view abstract10.1109/ICSENS.2013.6688529
  • Conceptual design of a dielectric hemispherical lens antenna with a congruent radiation pattern for beam steering applications
    Dahl, C. and Will, B. and Schulz, C. and Rolfes, I. and Baer, C. and Musch, T.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2013)
    In this contribution a dielectric hemispherical antenna allowing wide range beam steering for 24 GHz radar applications is presented. A feeding concept for a hemispherical lens is developed using the geometrical-optical lens approach, therewith a high gain of 24 dBi is achieved with a lens radius of 90 mm. The lens is fed by a corrugated horn antenna to provide a low side lobe level up to a steering angle of 50°. 3D-electromagnetic field simulations and measurements confirm the antenna performance in the chosen scenario. © 2013 IEEE.
    view abstract10.1109/APS.2013.6711308
  • Detection of programme making and special event devices in indoor channels
    Nalobin, A. and Dortmund, S. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2013)
    This contribution deals with the detection of programme making and special event applications by spectrum sensing. In particular the effect of site specific positioning of spectrum sensors is discussed and is of interest especially to cognitive systems. The procedure of energy detection of the devices is based on a stochastic fading channel performed by ray tracing analysis within an exhibition hall of Berlin. The results of spectrum sensing show a high dependence on the distance and on the number of sensors. © 2013 IEEE.
    view abstract10.1109/APS.2013.6711637
  • Investigation of interactions between plasmas and RF-diagnostics: Challenges of complex 3D-electromagnetic field simulations
    Schulz, C. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2013)
    3D-electromagnetic field simulations are an indispensable tool for a cost-effective development and characterization of novel radio frequency systems for plasma diagnostic. This contribution investigates the challenges, simulations have to cope with for a realistic modeling of interactions between probe and plasma. Using the Drude model, a plasma can be described as a dielectric material by its plasma electron frequency and collision frequency. This yields numerous variations of modeled plasmas, showing the resulting interaction processes. A comparison of simulation and measurement shows an excellent agreement, demonstrating the suitability of the presented simulation model. © 2013 IEEE.
    view abstract10.1109/APS.2013.6711749
  • Supervision and control of medical sterilization processes utilizing the multipole resonance probe
    Schulz, C. and Styrnoll, T. and Awakowicz, P. and Rolfes, I.
    2013 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2013 - Proceedings (2013)
    An innovative and sensitive plasma probe suitable for the supervision and control of low-temperature plasma sterilization processes is presented in this contribution. For heat or chemical sensitive materials, plasmas are an indispensable tool regarding the sterilization of surgery instruments, for example. The presented Multipole Resonance Probe (MRP) allows for the simultaneous determination of plasma density, plasma temperature, and collision frequency by a simple and fast evaluation of its frequency response. Fed by an rf-signal, the MRP yields sensitive and local measurements for the determination of lowest fluctuations and for the application of a sensor network, respectively. With a minimal distance of 3 cm between two probes, the MRP can be deployed effectively as sensor network inside the plasma for the supervision of its stability and homogeneity. Based on 3D-electromagnetic field simulations the advantages of the MRP are discussed in detail. Compared to a Langmuir probe, measurements in a Double Inductive Coupled Plasma (DICP) show the suitability of the MRP inside an argon plasma. © 2013 IEEE.
    view abstract10.1109/IMWS-BIO.2013.6756158
  • The multipole resonance probe: Evolution of a plasma sensor
    Schulz, C. and Rolfes, I. and Styrnoll, T. and Awakowicz, P. and Oberrath, J. and Mussenbrock, T. and Brinkmann, R.P. and Storch, R. and Musch, T.
    Proceedings of IEEE Sensors (2013)
    A robust and sensitive plasma probe, the multipole resonance probe (MRP), and its importance for industrial purposes is presented and discussed in this paper. Based on its innovative concept and its simple model of the system 'probe-plasma', a novel wall-mounted sensor is introduced. This sensor represents an optimized design of one sector of the MRP's assembly and is investigated within 3D-electromagnetic field simulations and compared to measurements of the MRP in an argon plasma. The resulting wall-mounted sensor can be designed for a desired application, which operates within a limited frequency range. The presented sensor covers a density range of approximately ne = 1016 m-3.. 1017 m-3, which is sufficient for the considered process. © 2013 IEEE.
    view abstract10.1109/ICSENS.2013.6688324
  • 9-GHz wideband CMOS RX and TX front-ends for universal radio applications
    Hampel, S.K. and Schmitz, O. and Tiebout, M. and Mertens, K. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 60 (2012)
    Wideband receiver (RX) and transmitter (TX) RF front-ends for wireless universal radio applications are presented. The RX is comprised of a two-stage low-noise amplifier (LNA) applying feedback and shunt peaking, a combiner buffer for performance boosting, and an inverter-based in-phase/quadrature (IQ) down-conversion mixer. The wideband LNA provides input matching of better than -10 dB from dc to beyond 10 GHz. The conversion gain (CG) of the RX front-end has a peak value of 31 dB with a 3-dB bandwidth up to 9 GHz. The minimal noise figure is 6 dB and kept below 9 dB within the entire operational bandwidth. The RX has a linearity in terms of intermodulation distortion of better than -12 dBm. The direct conversion TX involving inverter-based IQ modulator and Darlington-type pre-power amplifier features operation up to 9 GHz with 10-dB mean CG and an average output power of 4 dBm at 1-dB compression level. Excluding buffers and local oscillator generation, the RX and TX dissipate 54 and 84 mW, respectively, from a 1.2-V voltage supply. The circuit prototypes have been fabricated in a standard 65-nm CMOS low-power process without any additional RF options and occupy an area of only 0.77 mm 2 and 0.53 mm 2, respectively. © 2012 IEEE.
    view abstract10.1109/TMTT.2012.2183383
  • A multistatic feeding concept for beam steering based on a dielectric ellipsoidal antenna
    Schulz, C. and Baer, C. and Pohl, N. and Musch, T. and Rolfes, I.
    Asia-Pacific Microwave Conference Proceedings, APMC (2012)
    A simple and easy to integrate concept for multi-static beam steering using an existing dielectric ellipsoidal lens antenna is presented in this paper. Good antenna characteristics allow a modification of the antenna for the desired beam steering for industrial applications at 24 GHz. Based on the so-called geometrical-optical lens approach and 3D-electromagnetic field simulations the concept is investigated and the resulting effects of the modification are depicted. The antenna beam can be steered within a range only limited by the antenna dimensions. Using multiple feeding elements in one antenna within the same plane, a multistatic beam steering can be realized. For the multistatic approach, the circular waveguides for the antenna feeding are limiting the achievable steering angles, due to the minimal distance between two waveguides. Measurements of a first prototype confirm the expected behaviour and demonstrate the applicability for industrial purposes. Hence, the concept is suitable for the realization of multiple beam angles using only one antenna for a chosen number of feeding points. © 2012 IEEE.
    view abstract10.1109/APMC.2012.6421574
  • A new approach on broadband calibration methods for free space applications
    Will, B. and Rolfes, I.
    IEEE MTT-S International Microwave Symposium Digest (2012)
    The application of free space measurements depends on the practicability of the respective calibration procedure. Due to necessary changes of the distance between used antennas or a precise positioning of calibration standards, the suitability of free space setups is limited. This contribution deals with a calibration technique for free space applications, which uses the change of the electrical length by means of small frequency variations. Thus, this technique enables free space calibrations without the necessity of antenna displacements. Furthermore, the bandwidth of this procedure is not limited due to ambiguities of mechanical displacements during the calibration procedure. Additionally, the presented calibration technique is based on the Thru-Line-Network (TLN) method. Hence, symmetrical and reciprocal measurement objects can be characterized within the calibration procedure. © 2012 IEEE.
    view abstract10.1109/MWSYM.2012.6259615
  • A novel radio-frequency plasma probe for monitoring systems in dielectric deposition processes
    Schulz, C. and Styrnoll, T. and Lapke, M. and Oberrath, J. and Storch, R. and Awakowicz, P. and Brinkmann, R.P. and Musch, T. and Mussenbrock, T. and Rolfes, I.
    Proceedings of the 2012 International Conference on Electromagnetics in Advanced Applications, ICEAA'12 (2012)
    This paper presents a novel industry compatible plasma probe for monitoring systems in dielectric deposition processes. The probe is based on the so called active plasma resonance spectroscopy and allows an extensive evaluation of different important plasma parameters, needed for the supervision and control of the plasma deposition process. Due to its assembly, the probe is insensitive against additional dielectric coating. Hence, the measurement performance is not affected. 3D-electromagnetic field simulations of the probe in a pseudo plasma deposition process, as well as the measurement with a prototype in a real deposition process show a good agreement with the expected behaviour and confirm the applicability of the probe as a monitoring tool for dielectric deposition processes. © 2012 IEEE.
    view abstract10.1109/ICEAA.2012.6328725
  • A planar orthomode transducer for broadband applications at 25 GHz using a stepped waveguide technique
    Baer, C. and Schulz, C. and Will, B. and Rolfes, I. and Musch, T.
    Asia-Pacific Microwave Conference Proceedings, APMC (2012)
    In this contribution, a novel planar orthomode transducer is presented. It is based on a stepped waveguide technique that makes the transducer small and easy to handle. Several electromagnetic simulations were performed in order to optimize the transducer's structure and to investigate possible production tolerances, respectively. The developed orthomode transducer was built up and measured in a back to back assembly. The broadband measurement results as well as its planar structure allow different kind of feeding which make the presented orthomode transducer suitable for numerous applications. © 2012 IEEE.
    view abstract10.1109/APMC.2012.6421602
  • A time domain transmission measurement system for dielectric characterizations
    Will, B. and Gerding, M. and Schulz, C. and Baer, C. and Musch, T. and Rolfes, I.
    International Journal of Microwave and Wireless Technologies 4 (2012)
    Delay time measurements are a commonly used technique for the characterization of dielectric materials. Especially with regard to the characterization of water-solid mixtures like soil or grain delay time measurements, e.g., time domain reflectometry offers a powerful method. However, the accuracy of reflection measurements is limited due to multiple reflections caused by inhomogenities of the environmental material of the sensor. This contribution deals with an improved sensor design based on time domain transmission (TDT) measurements. Thus, the first received impulse includes the necessary information. Multiple reflections are received at later time steps and their influence on the measurement accuracy is nearly negligible. To improve the performance and the applicability of the designed sensor, a cost-efficient TDT system is designed, which is integrated in the sensor. Additionally, a so-called "concentric reversion coupler" is used, which offers the possibility to perform TDT measurements without the necessity of external measuring ports. © 2012 Cambridge University Press and the European Microwave Association.
    view abstract10.1017/S1759078712000347
  • Application of the thru-network-line self-calibration method for free space material characterizations
    Will, B. and Rolfes, I.
    Proceedings of the 2012 International Conference on Electromagnetics in Advanced Applications, ICEAA'12 (2012)
    Free space measurement systems can be used advantageously for non destructive and contactless material characterizations. These free space measurements are commonly performed with a four channel vector network analyzer, which allows the employment of self calibration methods. In this contribution a self-calibration procedure is investigated, which is based on a reciprocal and symmetrical network as one of the calibration standards. With regard to the characterization of dielectric materials the material under test can be described as a symmetrical and reciprocal network. Thus, the material under test can be used as a calibration standard within the self calibration procedure. Hence, the scattering parameters of the material under test are determined during the self calibration method. This contribution illustrates the application of the thru-network-line calibration method for free space material characterizations. This approach offers the possibility to perform free space material characterizations during the self calibration procedure without the necessity of any additional measurements. © 2012 IEEE.
    view abstract10.1109/ICEAA.2012.6328749
  • Determination of the delay spread of an indoor channel measurement campaign in the UHF band
    Sczyslo, S. and Dortmund, S. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2012)
    This contribution deals with the determination of the delay spread of the indoor channel within a large exhibition hall. The results are of special interest to Programme Making and Special Event applications, intending to operate in this typical scenario, and are representative for other applications within the entire UHF range. To determine the delay spread an ultra-wideband measurement campaign is carried out. Both the small scale as well as the large scale setup of the campaign are introduced in this paper. © 2012 IEEE.
    view abstract10.1109/APS.2012.6348846
  • Distance-dependent enhancement of a measurement based channel model for large concert halls
    Dortmund, S. and Sczyslo, S. and Rolfes, I.
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2012)
    This paper extends a previously presented indoor channel model for large concert halls. The enhancement includes large scale variations of wireless propagation channels inside of a typical scenario specifically intending for Cognitive Programme Making and Special Event applications (C-PMSE). Because of the frequency agile nature of a cognitive radio link, the statistical model is realized as a baseband multipath model in the time domain derived from an ultra wideband measurement campaign focusing on line of sight propagation channels. © 2012 IEEE.
    view abstract10.1109/APS.2012.6348005
  • On the fidelity of ultra-wideband antennas
    Sczyslo, S. and Rolfes, I. and Kaiser, T.
    Proceedings of the 2012 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, APWC'12 (2012)
    Within this contribution two ultrawideband antennas, an almost omnidirectional bi-conical antenna of type SBA 9113 from Schwarzbeck and a directional Vivaldi antenna, are analyzed according to their time-domain characteristics. In this context the fidelity factor and the peak value play an important role. Hence both, the parameter's definition is recaped and the particular practical meaning is explained. Moreover, a new parameter, the two antenna fidelity is introduced which indicates an antenna's performance in context of a typical point to point link involving two antennas. To increase the accuracy the analysis is based upon a resimulation of both antennas. © 2012 IEEE.
    view abstract10.1109/APWC.2012.6324990
  • A broadband stacked patch antenna with enhanced antenna gain by an optimized ellipsoidal reflector for X-band applications
    Schulz, C. and Baer, C. and Musch, T. and Rolfes, I.
    2011 IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems, COMCAS 2011 (2011)
    A broadband stacked patch antenna, based on an aperture coupled feeding with two patch elements is presented. The transmission line model is introduced as one possibility for the design of an aperture coupled antenna. 3D electromagnetic field simulations are used for optimization and allow a detailed investigation of the influence of the different antenna parameters on the return loss and the antenna gain. To minimize the effect of an undesired formed opposite side lobe of the antenna, resulting in a poor front-to-back ratio, an optimized ellipsoidal reflector is presented to focus the radiation in one main direction. A good return loss in a bandwidth of more than 4 GHz, i.e. 42 %, with a maximum antenna gain of 18.1 dBi is achieved. A first prototype verifies the simulation results and the functionality of the developed antenna design. © 2011 IEEE.
    view abstract10.1109/COMCAS.2011.6105928
  • Antenna impact on the gauging accuracy of industrial radar level measurements
    Armbrecht, G. and Zietz, C. and Denicke, E. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 59 (2011)
    This paper deals with a systematic evaluation of the antenna impact on the gauging accuracy of industrial radar level measurements for process automation. By this means, a framework is provided by which the antenna parameters of major influence on the gauging accuracy can be identified. Guidelines are given to what extent an improvement of these parameters results in a measurable accuracy increase. Firstly, the radar system theory for monostatic level gauging and the emulation of such radar systems by software and hardware are briefly reviewed. Secondly, an analytical model of traveling-wave endfire antennas is introduced, allowing to separately study the influence of individual antenna parameters on the distance measurement accuracy. Thus, a direct relationship between characteristic antenna properties, such as the level of the pattern attenuation in the direction of a parasitic scatterer, and the gauging performance is obtained. The investigations are conducted for one specific pulse-based barycentric signal-processing scheme, which is predestined for industrial level gauging due to its low complexity and reliability. Finally, the results are verified by measurements within a compact radar test range. © 1963-2012 IEEE.
    view abstract10.1109/TMTT.2011.2163075
  • Differential amplifier characterization using mixed-mode scattering parameters obtained from true and virtual differential measurements
    Schmitz, O. and Hampel, S.K. and Rabe, H. and Reinecke, T. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 59 (2011)
    This paper examines the differences in large signal mixed-mode scattering parameter characterization of differential amplifiers arising from virtual and true differential probing. The analysis is carried out by means of differential gain compression curves obtained from exemplary amplifier test assemblies with variable common mode rejection ratio. Based on analytical derivations involving basic nonlinear circuit theory, mathematical closed form transfer functions of these amplifiers are presented that enable an a-priori estimation of the occuring measurement error. Numerical simulations complete the theoretical investigations by giving additional physical insights onto the individual amplifier nodal voltages effecting the compression. Experimental results obtained from true and virtual differential compression curve measurements of the considered amplifier topologies are finally compared to the results gained from the theoretical considerations. Based on these results, the reason for the deviation between virtual and true differential measurements is addressed and upper and lower bounds for these deviations are given that are in accordance with the results reported in literature. © 2010 IEEE.
    view abstract10.1109/TMTT.2010.2084095
  • Plasma and optical thin film technologies
    Stenzel, O. and Wilbrandt, S. and Kaiser, N. and Schmitz, C. and Turowski, M. and Ristau, D. and Awakowicz, P. and Brinkmann, R.P. and Musch, T. and Rolfes, I. and Steffen, H. and Foest, R. and Ohl, A. and Köhler, T. and Dolgonos, G. and Frauenheim, T.
    Proceedings of SPIE - The International Society for Optical Engineering 8168 (2011)
    The PluTO project is aimed at combining thin-film and plasma technologies. Accordingly, the consortium comprises experts in optical coating (Laser Zentrum Hannover, Fraunhofer IOF) and such in plasma technology (INP Greifswald, Ruhr University of Bochum RUB). The process plasmas available, especially the sheath layers, will be thoroughly characterized by means of special probes, so that the types, numbers and energies of the particles participating in the coating formation processes can be determined comprehensively in every detail for the first time. The data thus obtained will provide a basis for a numerical modelling of layer growth at atomic scale (Bremen Center for Computational Materials Science BCCMS). The results are expected to deepen the understanding of the physical mechanisms responsible for the influence of plasma action on the layer properties. In parallel, suitable tools for process monitoring will be identified and made available. Some first results have already been achieved which prove the viability of the approach. © 2011 SPIE.
    view abstract10.1117/12.895323
  • The multipole resonance probe: Characterization of a prototype
    Lapke, M. and Oberrath, J. and Schulz, C. and Storch, R. and Styrnoll, T. and Zietz, C. and Awakowicz, P. and Brinkmann, R.P. and Musch, T. and Mussenbrock, T. and Rolfes, I.
    Plasma Sources Science and Technology 20 (2011)
    The multipole resonance probe (MRP) was recently proposed as an economical and industry compatible plasma diagnostic device (Lapke et al 2008 Appl. Phys. Lett. 93 051502). This communication reports the experimental characterization of a first MRP prototype in an inductively coupled argon/nitrogen plasma at 10 Pa. The behavior of the device follows the predictions of both an analytical model and a numerical simulation. The obtained electron densities are in excellent agreement with the results of Langmuir probe measurements. © 2011 IOP Publishing Ltd.
    view abstract10.1088/0963-0252/20/4/042001
  • Body effect up- and down-conversion mixer circuits for low-voltage ultra-wideband operation
    Schmitz, O. and Hampel, S.K. and Orlob, C. and Tiebout, M. and Rolfes, I.
    Analog Integrated Circuits and Signal Processing 64 (2010)
    This article presents fully differential up- and down-conversion mixer circuits manufactured in a triple well 45 nm CMOS process for low-voltage Ultra-Wideband transmitter and receiver applications. The proposed circuits both employ the transistor bulk terminal for signal injection. While the down-conversion mixer uses the bulk for switching via threshold voltage modulation, the up-conversion mixer applies the baseband signal to the bulk, thereby implicitly incorporating the back-gate controlled current source of the MOS transistor. Both circuits offer resistive on-chip termination and DC coupled output buffering for measurement purposes. The down-conversion mixer features an input-referred compression point of -13.2 dBm and a maximum conversion gain of 9.4 dB at 2.5 GHz with the 3-dB corner frequency being beyond 10 GHz. The implemented up-conversion mixer offers a maximum conversion gain of -8.8 dB at 5.8 GHz together with an output-referred compression point of -9.7 dBm. The operational bandwidth ranges from 4.5 to 6.7 GHz. Both circuits operate at a low supply voltage of 1.1 V. © 2009 Springer Science+Business Media, LLC.
    view abstract10.1007/s10470-009-9426-3
  • Effects of antenna characteristics and placements on a vehicle-to-vehicle channel scenario
    Kornek, D. and Schack, M. and Slottke, E. and Klemp, O. and Rolfes, I. and Kürner, T.
    2010 IEEE International Conference on Communications Workshops, ICC 2010 (2010)
    The time-varying propagation channel in vehicle-to-vehicle (V2V) communications strongly influences the performance of a wireless system in terms of e.g. channel capacity or outage probability. Assuming knowledge of the channel characteristics, in simulations these parameters are generally calculated by using isotropic radiators instead of real antennas, thus neglecting the influence of the antennas' parameters. Therefore, the goal of this paper is to investigate a possible antenna configuration consisting of three antennas mounted at different positions on the car and to describe the difference between the real and a corresponding isotropic configuration for a defined channel scenario. ©2010 IEEE.
    view abstract10.1109/ICCW.2010.5503935
  • Inductorless low-voltage and low-power wideband mixer for multistandard receivers
    Hampel, S.K. and Schmitz, O. and Tiebout, M. and Rolfes, I.
    IEEE Transactions on Microwave Theory and Techniques 58 (2010)
    This paper presents the design and implementation of a low power wideband mixer for multistandard receivers, covering global system for mobile communications, universal mobile telecommunications system, wireless local area network, Bluetooth, and ultra-wideband. The circuit topology is based on the folded technique with a current reuse shunt feedback RF input stage operating at a low supply voltage of 1 V. The mixer offers a peak gain of 12.8 dB, a 3-dB bandwidth from 1 to 10.5 GHz, and a minimum double-sideband noise figure of 7.6 dB. The input referred compression point is better than-15 dBm with an output referred intercept point of better than 5.75 dBm over the entire bandwidth. The mixer circuit was fabricated in a 65-nm standard CMOS process and draws 5 mA of dc current, leading to a power dissipation of only 5 mW. Gain and noise performance can be further increased when operating at nominal supply voltage of 1.2 V at the expense of an increasing power dissipation. Copyright © 2010 IEEE.
    view abstract10.1109/TMTT.2010.2042894
  • Load modulation for efficiency enhancement of inverse class-D power amplifiers
    El Din, M.G. and Geek, B. and Rolfes, I. and Eul, H.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    This paper presents the implementation of load modulation concept to inverse class-D power amplifiers, additionally an adaptive matching network suitable for differential applications will be presented. A 20 Watt inverse class-D amplifier at 1 GHz was designed and measured, with a maximum power added efficiency of 78%. Through using load modulation the amplifier can achieve a power added efficiency greater than 60% over 11 dB output dynamic range. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724207
  • Measurement based channel model for large concert halls
    Dortmund, S. and Schmidt, A. and Rolfes, I.
    2010 IEEE International Symposium on Antennas and Propagation and CNC-USNC/URSI Radio Science Meeting - Leading the Wave, AP-S/URSI 2010 (2010)
    The digital dividend has the goal to achieve a more efficient utilization of the UHF broadcasting bands by permitting access to cognitive radio devices. Thus, the conventional use of analog, narrow band devices by secondary users of the same frequency range is supressed. One traditional application of this type are common ProfessionalWirelessMicrophone Systems (PWMS). To maintain the production process of multimedia content with wireless audio technology, PWMS manufacturers and users are seeking for possible frequency and operation mode alternatives. Therefore, the propagation properties for typical PWMS applications, like concert halls, inside the UHF broadcasting bands and beyond have to be characterized. First steps for body worn devices were presented in [1]. © 2010 IEEE.
    view abstract10.1109/APS.2010.5561668
  • Minimal area 65nm CMOS amplifier for Ultra-Wideband transmitter applications
    Schmitz, O. and Hampel, S.K. and Mertens, K. and Tiebout, M. and Rolfes, I.
    2010 IEEE International Conference on Ultra-Wideband, ICUWB2010 - Proceedings 1 (2010)
    This work presents the design of an inductorless, monolithically integrated differential CMOS wideband amplifier covering the frequency range from 0.2 to 10.2 GHz, thus being a suitable candidate for full-band Ultra-Wideband transmitter applications. The amplifier is processed in a 1.2 V 65nm CMOS technology and is comprised of two pseudo differential current-reuse shunt-feedback stages combined with active inductor loads. Measurement results of the bonded chip show a power gain of 10.2 dB and return losses of better than -10 dB for the input and output respectively. The measured output referred 1 dB compression point is above 3.9 dBm within the entire specified frequency range. With a power consumption of 39 mW and a die size of only 370μm × 370μm, this circuit represents a capable minimal area alternative to classical distributed amplifier approaches focussing on that frequency range. © 2010 IEEE.
    view abstract10.1109/ICUWB.2010.5615693
  • Precise radar filling level measurements in Still pipes
    Denicke, E. and Armbrecht, G. and Rolfes, I.
    Technisches Messen 77 (2010)
    This contribution deals with guided radar distance measurements in the field of industrial tank level control. The aim is to achieve a submillimeter gauging accuracy even when conducting the measurement within the highly dispersive environment of large and thus overmoded cylindrical waveguides. In this case normally multimode propagation causes a decrease in measurement precision. Therefore, the effects of intermodal dispersion are fundamentally reviewed and based on these results two different approaches for overcoming the drawbacks of this measurement scenario are derived. On the one hand a prototype of a novel concept for compact mode-preserving waveguide transitions is presented, efficiently avoiding the excitation of higher-order modes. By applying this concept, free-space optimized signal processing algorithms can be used advantageously. On the other hand, an alternative correlation-based signal processing method is presented. The method is able to exploit the otherwise parasitic dispersion effects to enhance the measurement accuracy even in combination with an intentionally simple waveguide transition. Finally, the trade-off between the signal processing and the waveguide transition complexity is highlighted and discussed. Measurement results in a frequency range of 8.5 to 10.5 GHz are provided for different kinds of waveguide transitions proving the capability of both approaches. © Oldenbourg Wissenschaftsverlag.
    view abstract10.1524/teme.2010.0062
  • Radar distance measurements in circular waveguides involving intermodal dispersion effects
    Denicke, E. and Armbrecht, G. and Rolfes, I.
    International Journal of Microwave and Wireless Technologies 2 (2010)
    This contribution deals with guided radar distance measurements in the field of industrial tank level control. The aim is to achieve a submillimeter gauging accuracy even when conducting the measurement within a highly dispersive environment of large and thus overmoded circular waveguides. Normally, multimode propagation causes a decrease in measurement precision. Therefore, the effects of intermodal dispersion are fundamentally reviewed and, based on these results, a correlation-based signal processing method is presented. This method is able to exploit the otherwise parasitic dispersion effects to enhance the measurement precision even in constellation with a simple waveguide transition or antenna, respectively. Furthermore, considerations on the mode variety and its influence on the signal complexity as well as investigations on the technique's reliability and accuracy are presented. Measurement results in a frequency range of 8.5-10.5GHz are provided for three different kinds of waveguide transitions proving the capability of the method. © Cambridge University Press and the European Microwave Association 2010.
    view abstract10.1017/S1759078710000413
  • The multipole resonance probe: Realization of an optimized radio-frequency plasma probe based on active plasma resonance spectroscopy
    Schulz, C. and Lapke, M. and Oberrath, J. and Storch, R. and Styrnoll, T. and Zietz, C. and Awakowicz, P. and Brinkmann, R.P. and Musch, T. and Mussenbrock, T. and Rolfes, I.
    MECAP'10, 1st Middle East Conference on Antennas and Propagation (2010)
    A diagnostic concept is presented which enables the simultaneous determination of plasma density, electron temperature, and collision rate in low-pressure gas discharges. The proposed method utilizes a radio-frequency driven probe of particular spherical design which is immersed in the plasma to excite a family of spatially bounded surface resonances. An analysis of the measured absorption spectrum S(ω) of the probe provides information on the distribution of the plasma in its vicinity, from which the values of the plasma parameters can be inferred. In its simplest realization, the probe consists of two dielectrically shielded, conducting hemispheres, which are symmetrically driven by a radiofrequency source, and the excited resonances can be classified as multipole fields, which allows an analytical evaluation of the measured signal. A comparison of the analytical results, 3D-field simulations, and first measurements of a prototype show the functionality of the presented probe concept. © 2010-IEEE APS.
    view abstract10.1109/MECAP.2010.5724175
  • antennas

  • magnetism

  • microwaves

  • plasma diagnostics

  • sensors

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