14 June 2017 Identifying explosives using broadband millimeter-wave imaging
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Abstract
Millimeter wave imaging is employed in Advanced Technology Imaging (AIT) systems to screen personnel for concealed explosives and weapons. AIT systems deployed in airports auto-detect potential threats by highlighting their location on a generic outline of a person using imaging data collected over a range of frequency. We show how the spectral information from the imaging data can be used to identify the composition of an anomalous object, in particular if it is an explosive material. The discriminative value of the technique was illustrated on military sheet explosive using millimeter-wave reflection data at frequencies 18 – 40 GHz, and commercial explosives using 2 – 18 GHz, but the free-space measurement was limited to a single horn with a large-area sample. This work extends the method to imaging data collected at high resolution with a 18 – 40 GHz imaging system. The identification of explosives is accomplished by extracting the dielectric constant from the free-space, multifrequency data. The reflection coefficient is a function of frequency because of propagation effects associated with the material’s complex dielectric constant, which include interference from multiple reflections and energy loss in the sample. The dielectric constant is obtained by numerically fitting the reflection coefficient as a function of frequency to an optical model. In principal, the implementation of this technique in standoff imaging systems would allow threat assessment to be accomplished within the scope of millimeter-wave screening.
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James C. Weatherall, Kevin Yam, Jeffrey Barber, Barry T. Smith, Peter R. Smith, Joseph Greca, "Identifying explosives using broadband millimeter-wave imaging", Proc. SPIE 10189, Passive and Active Millimeter-Wave Imaging XX, 1018906 (14 June 2017); doi: 10.1117/12.2267192; https://doi.org/10.1117/12.2267192
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