A microwave measurement system for metallic object detection using swept-frequency radar

Abstract

Guns and knives have become a significant threat to public safety. Recently, a variety of techniques based on Electromagnetics (EM) have been used for their detection. For example, walk-through metal detection has been used in airports; X-ray and THz detection systems have been used for luggage screening. Different EM frequencies for metallic object detection have demonstrated different merits. This paper reports on a 1-14 GHz swept-frequency radar system for metallic object detection using reflection configuration. The swept frequency response and resonant frequency behaviour of a number of metallic objects, in terms of position, object shape, rotation and multiple objects have been tested and analysed. The system working from 1 to 14 GHz has been set up to implement sensing of metal items at a standoff distance of more than 1 meter. Through a series of experimental investigations, it can be found that the optical depths derived from the Fourier Transform of the power spectrum profile is in close relation with the relative location of the metallic object. The cross correlation between coherence-polarisation and cross-polarisation RF returns can be used to distinguish different objects. Therefore the optical depth and the cross correlation can be used as useful features for metallic object detection and characterisation in this portion of the microwave frequency spectrum.