Natural Resonant Frequency Extraction for Concealed Weapon Detection at Millimetre Wave Frequencies

The concealed weapon detection approach proposed in this paper is based on the extraction of the CNR (complex natural resonance) frequencies. An interrogating pulse is sent to the target under detection, thus its unique transient response associated with target geometry and material property is obtained. Complex natural resonant frequencies of a certain target are waveform and incidence aspect independent, and can be extracted from its late time response. The beginning of the late time response is estimated based on the distance between the interrogating source and the target, the dimension of the target and the width of interrogating pulse. The proposed procedure is numerically verified by using CST microwave studio and the optimization program - the genetic algorithm. Simulated results are compared with analytical solutions with good agreement. The procedure is readily applied to complex objects such as a handgun or knife.