Efficiency of using the spectral dynamics analysis for pulsed THz spectroscopy of both explosive and other materials

Abstract

One of the modern problems arising in the detection and identification of substances is a development of criteria for the assessment of a presence of explosive (or other dangerous substance) fingerprints in THz signals transmitted through or reflected from a sample. Obviously, criteria depend on the method used for the substance detection and identification. Taking into account our previous experience, we use for a solution of this problem the SDA method (method of the spectral dynamics analysis). Essential restrictions of usually used THz TDS method for the detection and identification under real conditions (at long distance about 3.5 m and at a high relative humidity more than 50%) are demonstrated using the physical experiment with paper napkins and thick paper bag. We show also that the THz TDS method detects spectral features of dangerous substances even in the THz signals measured in laboratory conditions (at distance 30-40 cm from the receiver and at a low relative humidity less than 2%) with semiconductors of different types used as samples. However, the integral correlation criteria, based on SDA method, allows us to detect the absence of dangerous substances in semiconductors. In order to demonstrate the possibilities of the integral criteria for finding additional substances in the mixture with semiconductors, we modeled several mixtures of n-doped Silicon with neutral substance Soap in different ratio. The discussed algorithms show high probability of the substance identification and a reliability of realization in practice, especially for non-destructive testing and security applications.

High effective THz-TDS method for the detection and identification of substances in real conditions

“…In [41] we showed the RDX, HMX and PETN explosives absence in the Si-based semiconductors with the help of integral correlation criteria (3)-(5). In the same manner, it is possible to show the absence of LTA and Sucrose in Si-35-12 and Si-40-12 samples.…”

“…In [30], [31] the integral criteria of probability assessment for the detection and identification of substance were proposed. In [32]- [36], [41] the spectral properties of THz pulses measured at long distances of about 3.5 meters were investigated by means of modified integral criteria.…”

Essential Limitations of the Standard THz TDS Method for Substance Detection and Identification and a Way of Overcoming Them

“…As our practice shows, to detect the presence of an explosive in a sample is a simpler task than proving its absence. Let us note that we have demonstrated the presence of explosives in the samples by means of the SDA-method and integral correlation criteria in a number of our previous papers, for example, in [ 15 , 20 , 24 , 25 , 26 ]. In particular, in [ 26 ] we showed the possibility to detect the explosive RDX in the plastic explosive PWM C4 with an inhomogeneous (rough and concave) surface in reflection mode using the integral correlation criteria (ICC).…”

“…In [ 19 , 20 ] the integral correlation and likeness criteria of probability assessment for the detection and identification of substance were proposed. In [ 21 , 22 , 23 , 24 , 25 ] the spectral properties of THz pulses measured at long distances of about 3.5 m were investigated by means of proposed modified integral criteria.…”

False detection of dangerous and neutral substances in commonly used materials by means of the standard THz Time Domain Spectroscopy

“…In [33] we showed the RDX, HMX and PETN absence in the n-Si and p-Si semiconductors with the help of integral correlation criteria in Eqs. (3)- (5).…”