Abstract
We have studied the spectral resolution influence on the accuracy of the substance detection and identification at using a broadband THz pulse measured under real conditions (at a distance of more than 3 m from a THz emitter in ambient air with a relative humidity of about 50%). We show that increasing spectral resolution leads to manifestation of small-scale perturbations (random fluctuations) in the signal spectrum caused by the influence of the environment or the sample structure. Decreasing the spectral resolution allows us to exclude from consideration this small-scale modulation of the signal as well as to detect the water vapor absorption frequencies. This fact is important in practice because it allows us to increase the signal processing rate. In order to increase the detection reliability, it is advisable to decrease the spectral resolution up to values of not more than 40% of the corresponding spectral line bandwidth. The method of spectral dynamics analysis together with the integral correlation criteria is used for the substance detection and identification. Neutral substances such as chocolate and cookies are used as the samples in the physical experiment.
Highlights
THz time-domain spectroscopy (THz TDS) is a common technique for substance identification
As the standard we use the THz signal transmitted through integral correlation between signal, these spectral intensities dynamics, it is possible to arrive the sample with the dangerous substance and measured in ideal conditions, or the signal measured in the atmospheric air, taking into account the known absorption frequencies of water vapor
We have demonstrated the essential limitations of the standard THz-TDS method for substance analysis based on a comparison of the substance spectrum under investigation and the standard substance spectrum from a database
Summary
THz time-domain spectroscopy (THz TDS) is a common technique for substance identification It is widely used for security problems [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17], non-destructive inspection of various materials [18,19,20], for biomedical [21,22,23,24,25] and pharmaceutical applications [26,27]. The description of the algorithm for the false absorption frequency elimination is one of the main purposes of our article Another distinctive feature of this work is the substance detection using both the time interval containing the main THz pulse and the time interval after the main pulse action, despite its strong noise. A computer simulation of a THz pulse interaction with disordered layered structures was made and the occurrence of false absorption frequencies in the spectrum of the signal transmitted through or reflected from such structure was explained
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