Dr.-Ing. Thorsten Schultze

Communication Systems
University of Duisburg-Essen

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  • High-Power Lensless THz Imaging of Hidden Objects
    Mansourzadeh, S. and Damyanov, D. and Vogel, T. and Wulf, F. and Kohlhaas, R.B. and Globisch, B. and Schultze, T. and Hoffmann, M. and Balzer, J.C. and Saraceno, C.J.
    IEEE Access 9 (2021)
    The potential of pulsed THz radiation for time-of-flight imaging applications is well recognized. However, advances in this field are currently severely limited by the low average power of ultrafast THz sources. Typically, this results in impractically long acquisition times and a loss in resolution and contrast. These limitations make imaging of the objects in real-life scenarios impossible. Here, conclusively, the potential of state-of-the-art high-average power THz time-domain spectrometer (TDS), driven by a 100-W class, one-box ultrafast oscillator for imaging applications is shown by demonstrating lensless THz imaging in reflection mode of a dielectric sample with low reflectivity. Images obtained with our home-built 20-mW average power THz-TDS system show a significant contrast enhancement compared to a state-of-the-art commercial THz-TDS with less than 200~mu text{W} of average power. Our unique setup even allows us to obtain images of such an object with high-contrast hidden inside a medium-density fiberboard (MDF) box. This opens the door to THz time-of-flight imaging of concealed objects of unknown shape and orientation in various real-life scenarios which were so far impossible to realize. © 2013 IEEE.
    view abstract10.1109/ACCESS.2020.3048781
  • High-Resolution Long-Range THz Imaging for Tunable Continuous-Wave Systems
    Damyanov, D. and Batra, A. and Friederich, B. and Kaiser, T. and Schultze, T. and Balzer, J.C.
    IEEE Access 8 (2020)
    Imaging in the terahertz frequency range has attracted growing interests since the first image of a leaf more than 20 years ago, due to its countless applications in basic and applied research, medical imaging, and nondestructive testing. However, most terahertz imaging approaches rely on focusing optics which require knowledge about the imaging scene before the actual imaging takes place. Further, imaging is mostly restricted to short distances and high resolution is only achieved for systems with a high bandwidth. Here, we present a method that enables high-resolution imaging of small metallic and dielectric objects at distances up to 2 m based on a synthetic aperture. We derive a simple approximation for the resolution of partial circular synthetic apertures with limited bandwidth. The bandwidth limitation is encountered by replacing the measured signals with replica signals of high bandwidth and equal round-trip time so that the resolution is only limited by the carrier frequency and signal-to-noise ratio of the measurement system. © 2013 IEEE.
    view abstract10.1109/ACCESS.2020.3017821
  • Spatiotemporal measurement of light extinction coefficients in compartment fires
    Arnold, L. and Belt, A. and Schultze, T. and Sichma, L.
    Fire and Materials (2020)
    In case of fire, the visibility plays a major role as it limits the occupants’ orientation capabilities and the perception of signs. These effects are determined by the light extinction due to smoke or other aerosols produced in fires. The presented method is based on the optical observation of an array of light sources during a fire in a laboratory experiment. The smoke induced into the compartment leads to a drop in intensity of each individual light source. This information is used to deduce the extinction along the line-of-sight to the camera. Once the data are captured, an automated processing is used to locate the diodes on the images and determine their intensity. Here, the optical image of the small diodes is assumed to have a known shape, so that the optimisation algorithm is capable to identify the location of the diode’s centre and quantify the luminosity in a sub-pixel range. The result is a time series for each diode, indicating the change of the relative luminosity, w.r.t. the initial values. Finally, a model for the extinction along each line-of-sight is formulated. It assumes that the light extinction coefficient is distributed in homogeneous layers. The number of layers is a free model parameter. Given this spatial distribution of the extinction coefficient and the experimental geometry, each line-of-sight is impacted by a number of layers, of yet unknown coefficient values. An inverse modelling approach is used here to find coefficient values that match the modelled line-of-sight extinction with the observed luminosity drops. The final result is a time- and height-dependent distribution of the light extinction coefficient during the full experiment. © 2020 John Wiley & Sons Ltd
    view abstract10.1002/fam.2841
  • High Resolution Image Processing Technique for the Detection of Metal Entrapments based on a Terahertz Camera
    Friederich, B. and Damyanov, D. and Kohl, J. and Kolpatzeck, K. and Liu, X. and Schultze, T. and Czylwik, A. and Balzer, J.C. and Willms, I.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019-September (2019)
    In this paper, we introduce a promising high resolution multistage approach for THz cameras for the detection and curvature extraction of metal fragments. The capability of this technique is demonstrated by detecting a 4 mm × 7 mm large metal fragment placed on a plank of beechwood. © 2019 IEEE.
    view abstract10.1109/IRMMW-THz.2019.8874437
  • High resolution lensless terahertz imaging and ranging
    Damyanov, D. and Friederich, B. and Yahyapour, M. and Vieweg, N. and Deninger, A. and Kolpatzeck, K. and Liu, X. and Czylwik, A. and Schultze, T. and Willms, I. and Balzer, J.C.
    IEEE Access 7 (2019)
    In this paper, we propose a fast terahertz time-domain imaging method using a radar migration algorithm. We demonstrate high-resolution imaging in reflection without any collimating or focusing optics in the terahertz beam. In the proposed method, the sample is illuminated with a divergent terahertz beam, and the receiver collects both specular and diffuse reflections. We further present calibration and post-processing methods that allow us to compensate for the inherently low signal-to-noise ratio of an unfocused terahertz beam. The feasibility of the novel imaging method is demonstrated with geometrically complex samples and a fast terahertz time-domain spectroscopy system based on electronically controlled optical sampling. We show that our concept is capable of generating images of the objects regardless of their size, shape, orientation and position relative to the transmitter and receiver antennas. Objects with edge lengths well below 400 μm can be clearly detected. The method presented here thus lends itself to arbitrary scenarios and antenna configurations. © 2013 IEEE.
    view abstract10.1109/ACCESS.2019.2934582
  • High Resolution Lensless THz Imaging with an Ultrafast TDS System
    Damyanov, D. and Friederich, B. and Kolpatzeck, K. and Liu, X. and Yahyapour, M. and Vieweg, N. and Deninger, A. and Schultze, T. and Willms, I. and Balzer, J.C.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019-September (2019)
    In this paper, we employ an ultrafast THz time-domain spectroscopy (TDS) system for computationally efficient imaging using a Kirchhoff migration algorithm. The imaging method makes use of uncollimated, unfocused terahertz beams, and eliminates the need for any opto-mechanical elements. Moreover, this method compensates for the low signal-to-noise ratio obtained with an uncollimated THz beam. We use a THz TDS system based on electronically controlled optical sampling (ECOPS), which achieves a measurement rate of 1600 traces per second. We validate the performance of the method with three different objects. © 2019 IEEE.
    view abstract10.1109/IRMMW-THz.2019.8873898
  • Preliminary analysis of candle flame impact on THz electromagnetic wave propagation
    Ghwaji, A. and Sheikh, F. and Schultze, T. and Willms, I. and Kaiser, T.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    This paper presents a preliminary analysis of candle flame impact on the ultra-broadband terahertz (THz) communication links across a spectrum of interest from 300 GHz to 310 GHz. This approach is based on complex transfer functions extracted from channel measurements using a vector network analyzer (VNA) to study the variations in total received power and phase. The channel measurements are performed in a lecture room under line-of-sight (LoS) environment. By evaluating the results, it turns out that the ray trajectories remain unchanged with candle flame but have slightly altered amplitudes of paths and phases. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823748
  • Spectroscopic Characterization of 3D Printed THz Rectangular Polymer Waveguides
    Liu, X. and Kolpatzeck, K. and Friederich, B. and Damyanov, D. and Haring, L. and Schultze, T. and Balzer, J.C. and Czylwik, A.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019-September (2019)
    In this paper, rectangular polymer waveguides for single-mode operation at 140 GHz are designed, simulated, and fabricated by 3D printing technology. The propagating mode is characterized by determining the attenuation constant and the effective refractive index of the waveguide using THz frequency-domain spectroscopy. Moreover, the change of the mode pattern with frequency is observed by performing transversal scans at the output of the waveguide. © 2019 IEEE.
    view abstract10.1109/IRMMW-THz.2019.8873855
  • Super-resolution restoration of low-resolution THz camera images
    Damyanov, D. and Friederich, B. and Kohl, J. and Liu, X. and Kolpatzeck, K. and Schultze, T. and Czylwik, A. and Balzer, J.C. and Willms, I.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    For the purpose of a high-precision object recognition (OR) system at THz frequencies, a 140 GHz super-resolution imaging system is presented in this paper. Conventional THz camera imaging systems are limited by their pixel numbers resulting in distorted and noisy low-resolution (LR) images hindering the possibility of correct object recognition. In this paper methods for improving the resolution of a 140 GHz camera are proposed based on super-resolution (SR) reconstruction methods typically used for low-cost optical components. The experimental validations are performed with a geometrically complex target. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823667
  • Wideband characterization of 3D printed THz rectangular dielectric waveguides by THz frequency-domain spectroscopy
    Liu, X. and Kolpatzeck, K. and Öztürk, A. and Friederich, B. and Damyanov, D. and Häring, L. and Schultze, T. and Balzer, J.C. and Czylwik, A.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    In this paper single-mode dielectric waveguides for 140 GHz are designed and fabricated by 3D printing technology. The waveguides are simulated using the finite difference time domain method and characterized by determining their frequency-dependent attenuation constant and frequency-dependent effective refractive index from 100 GHz to 180 GHz using THz frequency-domain spectroscopy. Furthermore, the mode patterns at different frequencies are observed by performing transversal scans of the far-field radiation pattern at the output of the waveguide. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823720
  • Wideband radiation pattern measurement of terahertz antenna-integrated photodiodes by frequency-domain spectroscopy
    Kolpatzeck, K. and Liu, X. and Friederich, B. and Damyanov, D. and Häring, L. and Schultze, T. and Balzer, J.C. and Czylwik, A.
    2019 2nd International Workshop on Mobile Terahertz Systems, IWMTS 2019 (2019)
    In this paper the potential of terahertz frequency-domain spectroscopy (THz-FDS) for wideband radiation pattern measurements of terahertz antennas is demonstrated. To this end, radiation patterns of a commercially available bowtie antenna-integrated photodiode are measured with a frequency resolution of 250 MHz from 100 to 400 GHz. Parasitic translation of the antenna during its rotation can be accurately resolved and compensated. Furthermore, by analysis in the time domain, the measurement setup can be examined for unwanted scatterers. © 2019 IEEE
    view abstract10.1109/IWMTS.2019.8823782
  • Wideband Radiation Pattern Simulation and Measurement of a Photodiode-Based Continuous-Wave THz Emitter
    Kolpatzeck, K. and Liu, X. and Nellen, S. and Friederich, B. and Damyanov, D. and Haring, L. and Schultze, T. and Globisch, B. and Balzer, J.C. and Czylwik, A.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2019-September (2019)
    In this paper, the radiation characteristics of a PIN photodiode-based terahertz emitter are simulated using the finite-difference time-domain (FDTD) method. The simulation results are validated by measurements from 100 to 400 GHz. Azimuth and elevation radiation patterns are compared and investigated in terms of beamwidth and sidelobes. © 2019 IEEE.
    view abstract10.1109/IRMMW-THz.2019.8874041
  • A novel estimation technique of the permittivity and the effective thickness of dielectric materials for wideband radar systems
    Friederich, B. and Tonder, S. and Schultze, T. and Willms, 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 novel estimation technique is introduced for a single measurement to estimate permittivity as well as the layer thickness of an object. The drawbacks of common characterization techniques, which require multiple changes in the measurement setup by sweeping the angle of incidence which just supply a narrow-band analysis of the permittivity are avoided. Furthermore, the reflection theory of multi-layer objects is briefly described so that the theoretical results are compared with measurements. By the comparison of the measurement and the simulation a validation of this model is possible. The introduced technique is ideal for autonomous security robotics where real-time conditions are necessary. Experimental validations are performed with two dielectric test objects. For the measurements the ZVB-20 network analyzer of Rohde & Schwarz is used working in a range from 4.5 GHz to 13.5 GHz. © 2017 European Microwave Association.
    view abstract10.23919/EURAD.2017.8249183
  • Object recognition radar system for partially reconstructed target image
    Damyanov, D. and Schultze, T. and Willms, I. and Salman, R.
    European Microwave Week 2017: "A Prime Year for a Prime Event", EuMW 2017 - Conference Proceedings; 14th European Microwave Conference, EURAD 2017 2018-January (2018)
    For the purpose of Radar Object Recognition (OR) system for real life scenarios where only a partially reconstructed image of the Object Under Test is available, an OR UltraWideband (UWB) Radar system is proposed. Conventional OR radar systems based on vector machines or neural networks result in a high recognition rates even for incomplete object images, but are not suitable for OR in a real time scenario due to the vast computational load. Hence the OR radar system proposed in this paper is based on a statistical approach employing a Bayesian detector and seven Object Recognition features with low mathematical and computational complexity. Furthermore, the proposed OR features are extracted from polarimetric radar images acquired by two imaging methods. Experimental validations are performed with an alphabet of twelve complex objects, a M-sequence UWB Radar device (4.5 GHz-13.5 GHz) and two compact dual-polarized Ultra-Wideband antennas. © 2017 European Microwave Association.
    view abstract10.23919/EURAD.2017.8249171
  • Super-Resolution FMCW Radar System at 60 GHz for 3D Measurements
    Damyanov, D. and Schultze, T. and Willms, I.
    2018 1st International Workshop on Mobile Terahertz Systems, IWMTS 2018 (2018)
    For the purpose of high-precision Radar Object Recognition (OR) system for real life emergency scenarios, a 60 GHz Super-Resolution FMCW radar imaging system is presented in this paper. Conventional radar imaging systems are limited by different hardware parameters such as bandwidth and antenna pattern resulting in distorted and noisy low-resolution (LR) images hindering the possibility of correct object recognition. Hence the radar imaging system proposed in this paper provides super-resolution (SR) images based on SR reconstruction methods typically used for low-cost optical components. Furthermore, the proposed SR radar system uses a low-cost single chip 60 GHz FMCW radar with two Rx antennas and one Tx antenna in a quasi monostatic configuration. The experimental validations are performed with geometrically complex targets by acquiring 3D radar images. © 2018 IEEE.
    view abstract10.1109/IWMTS.2018.8454688
  • A super-resolution polarimetric direct mapping imaging algorithm for a bistatic UWB-radar
    Damyanov, D. and Schultze, T. and Willms, I. and Salman, R.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    In this paper a real time capable 2D imaging method for ultra-wideband Radar is presented. A well known wavefront localization method is adapted and improved using a super-resolution wavefront extraction method and exploring the polarimetric information of the target under test. The imaging algorithm is real time capable and directly maps an extracted wavefront to the target contour in contrast to classical popular migration algorithms. Furthermore, the new proposed imaging algorithm is designed for a circular scanning trajectory, or a rotating target and a bi-static antenna configuration with two receiver antennas. Experimental validations are performed with a geometrically complex object, a M-sequence UWB Radar device (4.5 GHz-13.5 GHz) and compact Vivaldi Ultra-Wideband antennas. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461617
  • 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 enhanced super-resolution wavefront extraction algorithm for wideband FMCW radar systems
    Friederich, B. and Damyanov, D. and Schultze, T. and Willms, I.
    GeMiC 2016 - 2016 German Microwave Conference (2016)
    In this paper a novel super-resolution wavefront extraction algorithm is introduced that merges the advantages of the efficiency correlation techniques based on [1] and super-resolution ability of DCM techniques [2]. The introduced ADCM algorithm is based on the correlation method DCM, but in contrast this algorithm uses a set of weighted differently shifted reference pulses. Due to the clustering of wavefronts the computational effort of the wavefront extraction is optimized. In the herein used set-up a low-cost, single chip radar operating from 57 GHz to 64 GHz is applied. The low-cost and low-weight radar is ideal for autonomous security robots where real-Time conditions are necessary. © 2016 Institut fur Mikrowellen und Antennentechnik-IMA.
    view abstract10.1109/GEMIC.2016.7461552
  • 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
  • Polarimetric imaging method for a surface adaptive permittivity estimation for 60 GHz FMCW Radar
    Friederich, B. and Damyanov, D. and Schultze, T. and Willms, I.
    2016 10th European Conference on Antennas and Propagation, EuCAP 2016 (2016)
    The chaining of imaging techniques with material characterization capabilities is a very promising approach in the field of security applications. In this paper a polarimetric measurement setup which combines the advantages for imaging and material characterization is introduced. In the herein developed novel set-up the disadvantage of a bi-static configuration is overcome by the implementation of a retroreflector, allowing measurements applying a low-cost, single chip radar. This method is the basis for the combination of material characterization and imaging of targets with rough surface. Furthermore, a modified real time capable convergence algorithm based on [9] is proposed for the purpose of accurate imaging of rough objects. For the validation of this technique polarimetric measurements of real and rough objects are performed and the benefit of the polarimetric evaluation is shown. © 2016 European Association of Antennas and Propagation.
    view abstract10.1109/EuCAP.2016.7481938
  • A Novel Approach for Material Characterization Based on a Retroreflector Wide Band Transceiver Radar
    Friederich, B. and Schultze, T. and Willms, I.
    2015 IEEE International Conference on Ubiquitous Wireless Broadband, ICUWB 2015 (2015)
    The non-destructive material characterization is not only an interesting field for the academic research but also of importance for different applications, e.g. security applications. In this paper a noval measurement set up for low-cost 60GHZ wideband FMCW-radar is introduced. This set-up replaces the bi-static antenna configuration that is needed for reflection based permittivity estimation. This technique is an advancement of the established Microwave Ellipsometry [2]. The developed measurement technique and setup is called microwave retroreflector ellipsometry (MRE). The experimental validation is carried out with comparison with the well established delay time measurments (DTM) technique. Hence, different dieletric surfaces are examined. Finally the advantages of the MRE compared to the DTM are discussed. © 2015 IEEE.
    view abstract10.1109/ICUWB.2015.7324408
  • A super-resolution polarimetric wavefront extraction algorithm for UWB-radar under massive interference conditions
    Damyanov, D. and Salman, R. and Schultze, T. and Willms, I.
    International Journal of Microwave and Wireless Technologies 7 (2015)
    To provide short-range super-resolution ultra-wideband (UWB) radar under multi-scattering conditions, a superior wavefront extraction algorithm is proposed in this paper. Conventional correlation-based pulse separation methods based on SAGE, CLEAN or the previously introduced superior dynamic correlation method (DCM) are revised, validated, and compared. In this paper, the DCM is improved significantly by applying the Pauli scattering matrix decomposition onto the radar data. This novel wavefront extraction algorithm is called polarimetric dynamic correlation method (PDCM) and is suitable to resolve several overlapping pulses, which consist of both strong echoes and weak echoes which are masked by the strong ones. The performance of the PDCM and the comparison with alternative algorithms is carried out by a subsequent feature extraction algorithm for visual verification. Experimental validations are performed with two complex test objects, a maximum length sequence radar device (4.5-13.5 GHz) and compact dual-polarized UWB antennas. © Cambridge University Press and the European Microwave Association 2015.
    view abstract10.1017/S1759078715001233
  • Accurate 3D UWB radar super-resolution imaging for a bi-static antenna configuration
    Salman, R. and Norrdine, A. and Damyanov, D. and Schultze, T. and Willms, I. and Blankenbach, J.
    2015 International Conference on 3D Imaging, IC3D 2015 - Proceedings (2015)
    This paper deals with a real-time capable accurate 3D ultra-wideband radar imaging algorithm for complex shaped 3D objects including edges and corners. A well known wavefront based imaging algorithm is adapted to the bi-static 3D scenario which is, in contrast to the popular migration based algorithms, real-time capable and directly gathers the object contour coordinates. In order to reconstruct a accurate 3D object contour, the commonly proposed planar scan track (i.e. the planar aperture) of the antennas is modified and extended to a spatial scanning track with a circumnavigation of the object. To provide a more diverse radar signature the monostatic antenna configuration is extended to a bistatic configuration. Hence, the shape of the radiating wavefront is no longer spherical but ellipsoidal. Consequently, to ensure the super-resolution accuracy, the intersection point of 3 arbitrarily oriented and shifted ellipsoids in the 3 dimensional Euclidean space has to be determined. An iterative solution will be presented which utilizes the Gauss-Newton method to obtain a fast converging estimation with negligible error in the least-square sense. An experimental validation is carried out based on complex test objects with small shape variations relative to the used wavelength, an pseudo noise radar device (from 4.5 GHz to 13.5 GHz) and two tapered slot line Vivaldi antennas. © 2015 IEEE.
    view abstract10.1109/IC3D.2015.7391838
  • Feature based ultra-wideband object recognition
    Damyanov, D. and Salman, R. and Schultze, T. and Willms, I.
    Proceedings International Radar Symposium 2015-August (2015)
    For the goal of an Object Recognition (OR) in emergency situations, an OR Ultra-Wideband (UWB) Radar system is proposed in this paper. Conventional OR Radar systems based on vector machines or neural networks result in a high recognition rates, but are not suitable for OR in a real time scenario, due to the vast computational load. Hence the OR Radar system proposed in this paper is based on a minimum mean square error detector and seven Object Recognition features with low mathematical and computational complexity. Furthermore, the proposed OR features are extracted from polarimetric images Radar acquired by two imaging methods. Experimental validations are performed with an alphabet of twelve complex objects, a M-sequence UWB Radar device (4.5 GHz - 13.5 GHz) and compact dual-polarized Ultra-Wideband antennas. © 2015 German Institute of Navigation (DGON).
    view abstract10.1109/IRS.2015.7226278
  • Ultra-Wideband Radar Diffraction Approximation for Dielectric Edges
    Friederich, B. and Schultze, T. and Willms, I.
    2015 IEEE International Conference on Ubiquitous Wireless Broadband, ICUWB 2015 (2015)
    In this paper, a diffraction simulation for dielectric edges is introduced. The simulation is based on geometrical theory of diffraction (GTD) and is implemented as an improvement of the millimeter-wave surface characterization. This material characterization technique has been introduced in [1] and uses the microwave ellipsometry. The subject of current investigations is the usage of autonomous security robots for the detection of hot spots, the localization and characterization of objects. These robots should support fire brigades or disaster relief teams by millimeter-wave surface characterization. The developed technique was inspired by the established optical ellipsometry. The optical characterization technique does not consider the effect diffraction at the edges of the surface. Hence, the ellipsometry is limited to large surfaces where the diffraction effects can be neglected, but for the supposed application it is necessary to compensate these effects. © 2015 IEEE.
    view abstract10.1109/ICUWB.2015.7324523
  • A super-resolution polarimetric wavefront extraction algorithm for UWB-radar under massive interference conditions
    Damyanov, D. and Schultze, T. and Willms, I. and Salman, R.
    European Radar Conference EuRad 2014 (2014)
    To provide short-range super-resolution UWB Radar under multi-scattering conditions, a superior wavefront extraction algorithm is proposed in this paper. Conventional correlation based pulse separation methods based on SAGE, CLEAN or the previously introduced superior Dynamic Correlation Method (DCM) are revised, validated and compared. In this paper the DCM is improved significantly by applying the Pauli scattering matrix decomposition onto the Radar data. This novel wavefront extraction algorithm is called polarimetric DCM (PDCM) and is suitable to resolve several overlapping pulses which consist of both strong echoes and weak echoes which are masked by the strong ones. The performance of the PDCM and the comparison with alternative algorithms is carried out by a subsequent feature extraction algorithm for visual verification. Experimental validations are performed with two complex test objects, an M-sequence Radar device (4.5 GHz - 13.5 GHz) and compact dual-polarized Ultra Wideband antennas. © 2014 EuMA.
    view abstract10.1109/EuRAD.2014.6991209
  • Super-resolution feature extraction imaging algorithm for complex objects
    Damyanov, D. and Schultze, T. and Willms, I. and Salman, R.
    Proceedings - IEEE International Conference on Ultra-Wideband (2014)
    For the goal of an Object Recognition (OR) Radar system, a feature extraction algorithm is proposed in this paper. Conventional radar imaging method based on Kirchhoff Migration and the revised range point migration method are known to obtain fast and accurate images. However, these methods are not suitable for feature extraction as the Kirchhoff Migration method processes the whole evolution of the Radar data and the revised range point migration method extracts the coordinates of the target contour not features. Furthermore, the new proposed feature extraction algorithm is designed for a circular scanning trajectory, or a rotating target and a bi-static antenna configuration. The proposed algorithm calculates the target points from the a priori extracted wavefronts of the Object Under Test (OUT). A Polarimetric Dynamic Correlation Method (PDCM) is employed in the proposed algorithm for the extraction of the wavefronts. Experimental validations are performed with two complex OUT, a M-sequence Radar device (4.5 GHz-13.5 GHz) and compact dual-polarized Ultra-Wideband antennas. © 2014 IEEE.
    view abstract10.1109/ICUWB.2014.6958979
  • UWB-radar based surface permittivity estimation in hostile and pathless security scenarios
    Friederich, B. and Schultze, T. and Willms, I.
    Proceedings - IEEE International Conference on Ultra-Wideband (2014)
    Ultra-wideband radar analysis provides a high range resolution, which is not only important for ranging, but also for the material analysis of objects. This paper introduces a novel approach for a nondestructive and in-situ estimation of material characteristics. The developed technique was inspired by the already well established optical ellipsometry and is best suited for the remote inspection of hostile indoor scenarios with robots. The paper gives an overview about the technique and its current status of research and focuses on the realisation using only few mechanical components. © 2014 IEEE.
    view abstract10.1109/ICUWB.2014.6958963
  • Analysis of dust properties to solve the complex problem of non-fire sensitivity testing of optical smoke detectors
    Kruell, W. and Schultze, T. and Tobera, R. and Willms, I.
    Procedia Engineering 62 (2013)
    The purpose of an automatic fire detection system is the fast and reliable detection of arising fires in order to keep damage as low as possible. The European Standard EN54 defines a series of tests to prove and certify the functionality of smoke detectors, i.e. to prove that the detector is able to detect a fire in a prescribed period of time. Unfortunately the complex task of avoiding false alarms is not completely addressed. In contrast to the well standardized methods for the evaluation of the detection capability of a smoke detector, there is a lack of a reproducible and representative test method concerning the false alarm susceptibility with regard to nuisance aerosols. The consequences of false alarms should not be underestimated, as they may cause costs to serve the operator, especially in airborne applications. Many false alarms are caused by construction works in the surrounding of smoke detectors. For that reason several dust sources have been analyzed. Several approaches are possible and have been implemented to reduce the false alarm susceptibility of optical smoke detectors caused by dust and steam, e.g. different wavelengths and scattering angles. Unfortunately the developer has no representative test methods to quantify improvements and to point out the false-alarm resistance with e.g. a seal of quality due to new developments. Important is the knowledge of dust and steam properties such as the particle size distribution in comparison to particle size distribution of smoke of a fire. This paper presents a new approach for the test of smoke detectors regarding their susceptibility to false alarms due to nuisance aerosols, like steam and dust. The presented test apparatus is a very helpful and important tool for developers as well as for test houses during the developing and certification process. System designer will have a quantitative decision criterion to find the optimal detector for a specific place of installation. The paper compares the analysis of dust properties caused by construction works with standardized test dusts and shows how to solve the problem. © 2013 International Association for Fire Safety Science.
    view abstract10.1016/j.proeng.2013.08.136
  • Developments in non-fire sensitivity testing of optical smoke detectors - Proposal for a new test method
    Krüll, W. and Schultze, T. and Willms, I. and Freiling, A.
    Fire Safety Science (2011)
    The purpose of an automatic fire detection system is the fast and reliable detection of arising fires in order to keep damage as low as possible. The European Standard EN54 defines a series of tests to prove and certify the functionality of smoke detectors, i.e. to prove that the detector is able to detect a fire in a prescribed period of time. Unfortunately the complex problem of avoiding false alarms is not completely addressed. In contrast to the well standardised methods for the evaluation of the detection capability of a smoke detector, there is a lack of a reproducible and representative test method concerning the false alarm susceptibility with regard to nuisance aerosols. The consequences of false alarms should not be underestimated, as they may cause several costs to the operator, especially in airborne applications. Several approaches are possible to reduce the false alarm susceptibility of optical smoke detectors, e.g. different wavelengths and scattering angles. Unfortunately the developer has no test methods to quantify improvements due to new developments. This paper presents a new approach for the test of smoke detectors regarding their susceptibility to false alarms due to nuisance aerosols, like steam and dust. Fog and spray tests in the developed set-up are planned. The presented test apparatus is a helpful tool for developers as well as for test houses during the developing and certification process. System designer will have a decision criterion to find an adequate detector for a specific place of installation. The objective of the project was the development of a standardised test method for sensitivity tests of fire detectors to hazardous substances. The presented test apparatus has been developed in a cooperation of Airbus and the University of Duisburg-Essen and can contribute to a test standard. The design is similar to the EN54 test duct, however due to its small volume of only around 321, the duct is much smaller, easier to clean, portable and cheaper. The duct allows a qualitative statement on the sensitivity of the tested detector regarding nuisance aerosols with reproducible results. Also a slow pollution with dust of the measuring chamber can be emulated. The achieved results of this study are a promising first step in the development of a new test standard. © 2011 INTERNATIONAL ASSOCIATION FOR FIRE SAFETY SCIENCE.
    view abstract10.3801/IAFSS.FSS.10-543
  • Performance enhancement of UWB material characterization and object recognition for security robots
    Salman, R. and Schultze, T. and Willms, I.
    Journal of Electrical and Computer Engineering (2010)
    By means of UWB Radar sensors the tasks of material characterisation and object recognition can be performed on the basis of a previous imaging of the whole environment. A UWB version of the microwave ellipsometry method is applied for estimating the permittivity of homogenous objects. The object recognition task is performed using bistatic sensor nodes on the basis of Radar measurements. The simulation-based performance evaluations show a very robust behavior due to suitable preprocessing of Radar data. The applications comprise the detection of fire sources, the detection of metallic object hidden under clothing, and the recognition of building structures. © 2010 Rahmi Salman et al.
    view abstract10.1155/2010/314695
  • antennas

  • microwave antennas

  • radar imaging

  • ultra wideband radars

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