A swept millimeter-wave technique for the detection of concealed weapons and thin layers of dielectric material with or without fragmentation

Active millimetre wave systems, operating at frequencies up to 110 GHz have been used to detect the presence of both concealed dielectric and metallic objects at standoff distances. Co- and cross-polarized superheterodyne or direct detectors are used to differentiate between metallic and purely dielectric objects. The technique determines the thickness of a dielectric target and detects the presence of concealed handguns or fragmentation by utilising the pattern of the responses from both the co- and cross-polarized detectors. The returned signals are processed and analysed by an artificial neural network, which classifies the responses according to their correspondence to previous training data.