EUSAR 2014
Luggage Scanning at 80 GHz for Harbor Environments Jochen Moll, Viktor Krozer, Goethe University Frankfurt am Main, Germany, E-mail:
[email protected] Ralph Zimmermann, Björn Rolef, Rahmi Salman, Maxonic GmbH, Wachtberg, Germany Timo Jaeschke, Institute for Integrated Systems, Ruhr-Universität Bochum, Germany Nils Pohl, Millimeter Wave Radar and High Frequency Sensors (MHS), Fraunhofer FHR, Germany
Abstract In this paper, we present the results of a security-related case study using an 80 GHz millimeter-wave scanner with a large bandwidth of 25.6 GHz. The scanning system is based on a single transceiver that can be translated in two dimensions. By means of synthetic aperture radar (SAR) signal processing it is possible to calculate 3D-images for the detection of concealed objects. Imaging results will be present here for a knife and a revolver within a leather briefcase.
1
Introduction
Millimeter-wave imaging systems of active and passive type have been used successfully in recent years to detect concealed objects using low power electromagnetic irradiation [1]. Millimeter-waves at current power-densities are safe for humans and provide a wavelength that is short enough for imaging small objects [2]. This approach is not only attractive for security inspections at airports but also for other public spaces such as harbour environments. Special attention is dedicated here to the non-invasive analysis of baggage and parcels in order to find explosives, weapons as well as chemical or biological threats. Synthetic aperture radar processing at W-band provides high lateral resolution using antennas with small aperture. It has been shown in [3] that millimeter waves can be used to penetrate dielectric materials and to image concealed objects inside luggage with high spatial resolution. Other examples of millimeter-wave SAR-processing can be found in non-destructive material evaluation to find defects in structures of glass-fiber reinforced plastics [4]. Recently, SAR-processing has been demonstrated at Terahertz-frequencies of 514 to 565 GHz [5]. The contribution of this paper is to study the threedimensional imaging performance of the proposed single-pixel luggage scanner. Therefore, basic studies have been performed using a corner reflector. In addition, several metallic objects have been analyzed such as a revolver and a metallic knife within a leather briefcase.
2 2.1
Experimental Setup Description of the Luggage Scanner
A fast two dimensional scan in combination with high resolution range processing offers the capability to assess the third dimension using the inherent ability to determine range and such to construct a three dimensional im-
age of the content of a suitcase or parcel [6]. Figure 1 shows the image of the mechanical scanner where the 3D image reconstruction is based on the well-known backprojection technique [7].
Figure 1: Mechanical setup of the 2-D Scanner [6].
2.2
Radar Module
3D imaging applications demand for small and isotropic resolution cells to allow a good image quality of the scanned object. In X-Y direction this can be achieved by small antennas combined with synthetic aperture radar (SAR) processing. In Z direction a high range resolution can only be achieved by using ultra wideband radar sensors. For the presented measurements an 80 GHz FMCW radar system with 25.6 GHz bandwidth is used [8]. The radar sensor is based on a SiGe transceiver MMIC manufactured in Infineon’s B7HF200 technology which allows cost effective and mass production suitable mmWave chip designs. Figure 2 shows a block diagram of the complete radar system. All mmWave signal generation and receiving
ISBN 978-3-8007-3607-2 / ISSN 2197-4403
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Rogers RT5880 Substrate
1.4 - 7.8 GHz SiGe MMIC
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Ref. XCO 100 MHz
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mmWave-PLL
W-Band Waveguide Transition
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VCO 80 GHz
RF
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Auxiliary PLL Integer Static Frequency
RF-Signal: 68 - 93.6 GHz
VCO 24.8 GHz
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Bond Wires
Mixer IF
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USB PC-Interface Data Acquisition & Signal Processing with MATLAB
Figure 2: Block diagram of the FMCW radar system, including the offset mixing auxiliary PLL, the mmWave-PLL to generate the RF-signal, the waveguide transition, and the IF processing stage. blocks are integrated in the MMIC to ensure reliable operation of the RF components. A bond-wire compensation network is used to form a well matched differential bond wire transition between the chip and the Rogers RT5880 Duroid laminate which contains a rat-race coupler based differential to single-ended transition and a W-band waveguide transition. The FMCW frequency ramp is generated by an offset PLL concept which allows highly linear fractional ramp generation with an outstanding bandwidth. An off-the-shelf Hittite HMC704 PLL synthesizer chip is used for stabilisation of an auxiliary VCO at 24.8 GHz. The 80 GHz mmWave signal is divided by 4 and then mixed in a reverse frequency position with the 24.8 GHz signal, which leads to a loop gain compensation and easyto-manage output frequencies lower than 8 GHz which are suitable for use with an Hittie HMC701 fractional PLL synthesizer with integrated ramp generation. An I.F. amplification, filtering and digitalization stage with an build in USB interface for easy integration into data collecting and signal processing solutions like MathWorks MATLAB completes the system [9].
3 3.1
3.2
Threat Detection
Figure 4(a,b) shows a knife standing on a tripod with absorption material in the background. This represents almost ideal conditions since multi-path propagation effects can be neglected. The corresponding image reconstruction illustrates a vertical cross-range slice through the 3D voxel volume. One can clearly identify the shape of the knife with a high image dynamic. Small details can be observed such as the three metallic bolts. A second example is a metallic revolver in Figure 4(c,d). Note that the handle of the revolver is partially inside a foam material that produces signal attenuation and reduces image quality in this region. However, the shape of the gun can be clearly identified and the image dynamics is again >30 dB. Finally, we show the knife and the revolver in a leather briefcase in Figure 4(e,f). Both, the knife and the revolver (not shown) can be detected clearly at their correct location in the briefcase. This result proves that the proposed scanning system can be used for remote detection of metallic objects inside luggage.
Imaging Results 4
Corner Reflector Imaging
Conclusions
The following section demonstrates the first experimental imaging results with the proposed luggage scanner. The well-known backprojection technique is used here for 3D-imaging on a delay-and-sum basis. The raw range profiles are windowed with a Tukey-window to minimize sidelobes in range-direction. Moreover, a splineinterpolation scheme is used to read the reflectivity values from the range profiles.
This paper presented a luggage scanner operating at Wband for the detection of threats. 3D-images can be produced by adequate monostatic SAR-signal processing. Further studies will investigate the potential of using this system for imaging dielectric materials.
The performance of the wideband imaging system is demonstrated in Figure 3 using a corner reflector that is located at (0.004,0.615,-0.009)m. The measured pointspread-function at -6dB has a size of Δx = 9mm, Δy = 10mm and Δz = 11.5mm, respectively.
The authors acknowledge the technical support of the TeraSCREEN-project (http://www.fp7-terascreen.com). Viktor Krozer is grateful for funding by Oerlikon AG. Ralph Zimmermann is grateful for the financial support from the VESPERplus project.
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ISBN 978-3-8007-3607-2 / ISSN 2197-4403
Acknowledgements
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Figure 3: Imaging results of a corner reflector: (left) planar slices at the location of the corner reflector (0.004,0.615,0.009)m; (right) Characterization of the imaging performance at-6dB in (x,y,z)-direction.
References [1] V. Krozer, T. Löffler, J. Dall, A. Kusk, F. Eichhorn, R.K. Olsson, J.D. Buron, P.U. Jepsen, V. Zhurbenko, and T. Jensen. Terahertz imaging systems with aperture synthesis techniques. IEEE Transactions on Microwave Theory and Techniques, 58(7):2027–2039, 2010. [2] M.C. Kemp. Millimetre wave and terahertz technology for detection of concealed threats - a review. In 32nd International Conference on Infrared and Millimeter Waves (IRMMW), pages 647–648, 2007. [3] M. Haegelen, S. Stanko, H. Essen, G. Briese, M. Schlechtweg, and A. Tessmann. A 3-d millimeterwave luggage scanner. In Infrared, Millimeter and Terahertz Waves, 2008. IRMMW-THz 2008. 33rd International Conference on, pages 1–2, 2008. [4] J. Moll, M. Manavipour, C. Sklarczyk, V. Krozer, and C. Boller. Millimeter-Wave Non-Destructive Testing of a Cured in Place Pipe Sample. In 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW), pages 1–2, Mainz, Germany, 2013.
[5] J. Ding, M. Kahl, O. Loffeld, and P.H. Bolivar. Thz 3-d image formation using sar techniques: Simulation, processing and experimental results. Terahertz Science and Technology, IEEE Transactions on, 3(5):606–616, 2013. [6] H. Essen, R. Zimmermann, J. Moll, V. Krozer, B. Klein, and I. Krämer. A Four-Element 80-GHz Luggage Scanner Based on the Synthetic Aperture Radar Principle. In International Radar Symposium, pages 847–852, Dresden, Germany, 2013. [7] LeRoy A. Gorham and Linda J. Moore. Sar image formation toolbox for matlab. In Proc. SPIE, volume 7699, pages 769906–769906–13, 2010. [8] N. Pohl, T. Jaeschke, and K. Aufinger. An ultrawideband 80 ghz fmcw radar system using a sige bipolar transceiver chip stabilized by a fractional-n pll synthesizer. Microwave Theory and Techniques, IEEE Transactions on, 60(3):757–765, 2012. [9] N. Pohl, T. Jaeschke, and M. Vogt. Ultra high resolution sar imaging using an 80 ghz fmcw-radar with 25 ghz bandwidth. In Synthetic Aperture Radar, 2012. EUSAR. 9th European Conference on, pages 189– 192, 2012.
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Figure 4: Imaging results of the luggage scanner: (a,b) optical image and reconstruction of a metallic knife on a tripod; (c,d) optical image and reconstruction of a metallic revolver on a tripod; (e,f) optical image and reconstruction of a metallic knife in a leather briefcase.
ISBN 978-3-8007-3607-2 / ISSN 2197-4403
© VDE VERLAG GMBH  Berlin  Offenbach, Germany
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