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Detecting dielectric properties of objects imaged on persons in millimeter-wave AIT systems

Advanced Imaging Technology (AIT) uses millimeter-waves for airport passenger screening. The Identification of Explosives (IDX) technique addresses secondary screening of detected anomalies by analyzing the reflectivity data across the frequency band of the imaging system to probe the electrical permittivity of the potential threat. To be practical, IDX must apply to targets that are not configured for free-space metrology, but have poorly defined surfaces and are imaged with non-ideal boundaries. In particular, the magnitude of the reflection coefficient, which is key to free-space measurement, cannot be obtained with any confidence. The detection is accomplished from frequency-dependent features in the interference spectrum, which provide material identifying information in the form of the dielectric loss tangent.