21 May 2014 3D THz range finder of concealed objects
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Abstract
Numerous applications require fast and accurate range measurement of concealed objects. As THz waves penetrate almost all materials except metals, they are a candidate to perform this task. In this paper a system consisting of an illumination THz source and a THz detector array is presented. A solid state 300GHz THz source signal is frequency modulated and guided to a detector array using a beam splitter. The detector array consists of ultra-sensitive bolometers with 1000V/W sensitivity and NEP of 5pW/√Hz. Their square law sensitivity characteristic allows mixing of the reflected wave with the illumination wave, resulting in a mixed product with a difference frequency of few kHz proportional to the target distance, the frequency modulation span, and its rate. Parallel signal processing of all 16 signals results in fast range detection of the target. All 16 detectors provide four readings per second for all X and Y positions of the image. A compact and portable system with 40GHz frequency modulated source provides Δf/Δt = 160GHz/sec. This corresponds to a 1kHz difference frequency per one meter distance of the target. A resolution accuracy in the micrometer range has been achieved using advanced signal processing. In the paper the processing algorithms and the obtained results are presented and discussed. The complete hardware structure of the system is described together with the required signal processing procedures. The advantage of the presented system is that it operates at room temperature and is therefore cost effective and very robust.
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Janez Trontelj, Aleksander Sešek, Andrej Švigelj, "3D THz range finder of concealed objects", Proc. SPIE 9102, Terahertz Physics, Devices, and Systems VIII: Advanced Applications in Industry and Defense, 910206 (21 May 2014); doi: 10.1117/12.2052200; https://doi.org/10.1117/12.2052200
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