2D THz signature for substance identification

The method, which gives us a possibility to obtain the unique 2D signature of substance, for its identification in THz frequency range is developed and applied for the treatment of signals, passed through ordinary materials or selected explosives, including those hidden under opaque simulant covers. The method of identification is based on the analysis of spectrum dynamics (spectrogram) of medium response and has the ability not only to detect the presence of the substance in the sample but to identify it by its 2D signature, which is unique for each investigated substance. It allows to trace the dynamics of many spectral lines in one set of measurements simultaneously and to obtain the full information about the spectrum dynamics of the measured signal. We showed that spectrograms of THz pulses, passed through the explosives, hidden under simulant covers, widely differ from spectrograms of simulant themselves despite of a little difference in their Fourier spectra. Therefore, the method allows detecting and identifying the hidden substances with high probability and can be very effective for defense and security applications. The problem of detection of a noisy regular acoustic signal with linear modulation of frequency is examined too.