Detection of handguns by their complex natural resonant frequencies

The decomposition of the late time, transient response of metallic objects illuminated with broadband microwave energy into damped sinusoidal signals which are characterised by aspect-independent poles, is used extensively as a method of radar identification of aircraft and missiles. This method is utilised here for the detection and discrimination of handguns and non-threatening items, such as mobile phone handsets, cameras, keys and pens. It is of critical importance to explore the limits of this method, if it is to be utilised for the detection of such objects concealed on the human body or in bags carried on or close to the body that the limits of this technique is explored. Here, investigation is made by computer modelling of the complex natural resonances of two different handguns and these are compared with those for two non-threat items: a mobile phone handset and a fountain pen. Dependence of pole positions on small details present on a handgun is also investigated as is the effect of combining threat and non-threat items in close proximity. A way of enhancing the natural resonances by the use of a cross polarised receiver is also investigated.