The method of the spectral dynamics analysis of reflected signal for problem of identification of substance

Abstract

The method of spectral dynamics analysis (SDA-method) is used for the detection and identification of explosive RDX and harmless substances in pellets with different weight and hidden under the thin layer of polyethylene or cotton by reflected THz signal. The signal was measured on the long-term interval with duration about 180 ps and contains not only the main reflected THz pulse but the subpulse with less intensity. Two cases of the reflection were investigated - at 90° and at 45° from the sample. SDA method allows to obtain the spectrogram - 2D THz signature of the substance, and to analyze the dynamics of many spectral lines of the signal by one set of measurements. The identifiers characterizing the presence of substance in the sample were found in all investigated samples - they contain in the corresponding spectrograms and dynamics of spectral lines. We showed that the analysis of the reflected signal over the short time intervals (less than 50 ps) is insufficient for reliable identification of the substances, especially of hidden ones, because in some cases the characteristic features of the substances can be found only in the subpulses. The influence of window shape in Fourier-Gabor method on the dynamics of spectral lines was discussed too.