Concealed Weapon Detection Using Acoustic Spectral Characterisation

Abstract

This paper focuses on showing how one could identify a component by using acoustic waves within the audible frequency range. The purpose of this study is to incorporate the findings from this paper in concealed weapon detection (CWD) where objects hidden behind a person’s clothing could be detected using acoustic or ultrasonic sound waves. Experimental trials are carried out using a directional speaker which generates a highly directional acoustic beam. This can then be pointed at any target and the sound reflected from it analyzed. Initially, a sound source is selected based on the maximum frequency range. The characteristic of the acoustic signal produced by the source is then recorded to be used as reference. Different objects are selected to be used as targets. The sound reflected from these objects is recorded. The spectrograms from these targets reveal that the incident sound waves have been modulated. By taking the ratio of the reflected and the incident sound signals one could obtain the natural frequencies of the object and the spectrogram of the reflected acoustic signal could give indication of the object’s shape.