Research On Explosive Detection Technology Based On Terahertz Spectroscopy

Terahertz spectrum generally refers to the 0.1THz~10THz band of electromagnetic radiation. The frequency of Terahertz is located between microwave and infrared in the electromagnetic spectrum. In a broad sense, Terahertz also refers to the infrared radiation between 0.1THz~100THz. Compared with other electromagnetic radiation, Terahertz radiation has the special properties of transient, broadband, low energy and penetrability, etc. With the development of transportation and the increasing security at ports and stations, people pay more attention to the requirements in the field of safety inspection instrument and method.Many explosive materials have different characteristic absorption peaks, a property of "fingerprint", in Terahertz band. Terahertz spectroscopy technology can provide information which can not be obtained by traditional detection techniques such as microwave and X-ray technology. Terahertz detection technology processes a broad application prospects in military fields such as explosive detection, landmine detection, military communication, and civil domain application such as security checking and medical imaging.The research contents include:(1) The properties of Terahertz wave, principles of detection and development situation of explosives were described. A method of explosives detection based on terahertz spectra was proposed. The simulation, experiment and results analysis were carried out.(2) The basic principle of typical explosives and the simulation method of terahertz spectrum of explosives were introduced. The preparation process of explosives was studied.(3) Terahertz spectra of eight kinds of explosives(PETN, TNT, HMX, LLM105, RDX,DNAN, HNS, DNMT) at the band of 0~60THz were obtained by the means of molecular dynamics method.(4) The terahertz spectroscopy detection systems based on time-domain spectroscopy was built to realize the terahertz spectrum detection of explosives. The spectral analysis was carried out by fuzzy clustering and linear regression method. Finally, the relationship between the absorption peak and the chemical bond was studied.Our detailed research work and innovative aspects are mainly as follows:(1) Thought molecular modeling, structural optimization and frequency calculation with molecular dynamics of Gaussian software, the terahertz spectra of eight kinds of typical explosives such as PETN, TNT, HMX and LLM105, were simulated. Explosives have strong absorption in the range of 10THz~60THz, and there are also smaller absorption signal in the0.1THz~10THz band. The data of spectrum at the band at 0.1THz~10THz were further extracted by Matlab software.(2) Tablet and powder of PETN,TNT,HMX,LLM105,RDX and other explosives were detected by Fourier transform infrared spectrometer. We obtained the absorption spectroscopy of explosive at band of 10.5THz~60THz and extracted characteristic absorption peak. The position of the characteristic absorption peak is in agreement with the simulation results.(3) Terahertz time-domain spectroscopy system(THz-TDS) was built. Terahertz absorption spectroscopy of RDX,HMX,insensitive RDX,insensitive HMX,LLM105 were measured and the characteristic peak at band of 0.1THz~2.5THz were extracted. The position of the characteristic absorption peak is in agreement with the simulation result.(4) In order to facilitate public security applications, handhold MINI-Z Terahertz spectroscopy was used to detect the reflection and transmission spectra of powder explosive of HNS,DNAN, DNMT(spectral range from 0.1THz to 2.5THz). The characteristic absorption coefficient, the absorption spectra, reflectance spectra, reflectance, and transmittance of TNT were measured by a portable TAS7500 SP spectrometer from 0.5THz to 4THz.(5) We used fuzzy clustering method to classify a variety of explosives(RDX, HMX,DNAN, HNS, DNMT, LLM105). It laid a foundation for the further establishment of terahertz spectra database. Linear regression method was used to analyze the various quantity of RDX.It illustrated the feasibility of the Terahertz time-domain spectroscopy in quantitative analysisof explosives.(6) From the point of molecular dynamics, the characteristic absorption peaks of HMX and DNAN were calculated by Dmol3 module of Masterial Studio. The vibration modes of HMX and DNAN at characteristic frequency were analyzed by visualization module. The generation of the characteristic absorption peak was closely related to the vibration, twist,rotation and the stretching vibration of the chemical bond.The above studies lay the foundation for enriching the spectrum of explosives, establishing the terahertz fingerprint library of explosives, and the application of public safety and security.