| Drugs and terrorism are two big tumors in today’s world, which cause serious damage to the human safety and health. As countries all over the world are striking sever blows to drug-related and terrorist criminal activities which seriously endanger the society, criminals are unceasingly updating their means of committing crimes. To fight against drug-related and terrorist crimes has become a common goal of the world’s governments and international organizations. To achieve this goal we must first solve the problem of on-site rapid detection of drugs and explosives. During actual detection in places of public security, in addition to detecting the conventional drugs such as heroin, cocaine, cannabis, we also need to detect the raw material of drugs namely the precursor chemicals. Meanwhile, we have managed to detect the conventional explosives such as TNT. However, we urgently need technology and equipment to rapidly on-site detect liquid explosives and bums which cause more of a threat to public safety due to their complex composition, similar quality, convenient sources of raw materials and simple processing. So the project is mainly studying the detection of drugs, explosives and liquid dangerous materials.Main techniques and methods of detecting drugs, explosives and liquid dangerous materials home and abroad include test paper and chemical reagent method, electromagnetic method, optical method and spectroscopy, ion mobility spectrometry, chromatography and mass spectrometry method, ultrasonic method X-ray detection, etc. All these detection technology and methods have advantages and disadvantages. Test paper and chemical reagent method is easy operated and dispenses with electricity or battery drive, but it belongs to destructive testing, and one paper or reagent can only detect one certain material. Electromagnetic methods mainly include nuclear magnetic resonance (NMR), terahertz, microwave detection method and so on. The disadvantage of nuclear magnetic resonance (NMR) is long detection process and inability to detect liquid explosives containing no element. The detecting precision of the terahertz is greatly influenced by the environment. The common defects of electromagnetic detection methods are inability to detect liquid wrapped or sealed by metal. Optical detection methods are mainly using Raman and infrared spectrum detection instrument. Optical instrument testing is nondestructive testing, but it can only detect materials with transparent packaging and optical propagation path susceptible to other substances’interference may lead to measuring error. Ion migration spectrum method is destructive testing and unable to detect liquid in an airtight container essentially. Meanwhile, its low electronic stability and measuring accuracy easily influenced by different calibrations according to different measurement environments result in high error detection rate. Chromatography and mass spectrometry detection method has the advantage of high accuracy, but it also has disadvantages of complex detection process, slow speed, high cost and destructive testing, etc. Ultrasonic detection has advantages of the portable test instrument, safe and easy operation, but you have to measure the container size in advance and the detection precision is largely affected by echo.Compared with the drug/explosive detection methods mentioned above, X-ray detection method has advantages of non-destructive testing, non-contact testing, high resolution, low cost, strong penetrability and basically harmless to human body with low dose. Therefore, the domestic and foreign public security inspection instruments are basically given priority to X-ray detection method. X-ray detection technology is mainly identified by means of the density of material, images, and atomic number. While using X-ray to detect drug/explosive at home and abroad has made some progress, there are still some limitations:X ray detection technique can only obtain the material’s shape, density and the atomic number, but unable to discern materials with similar density. It can only obtain liquid material’s one-dimensional or two-dimensional information, but unable to distinguish liquids of different concentrations or mixed multi-component liquid. Moreover, its detecting speed is slow, which makes it difficult to meet the requirements of on-site rapid detection in the field of public safety.In recent years, with the progress of X ray theory and detection technology, energy dispersive X-ray scattering with broadband and wavelength scanning becomes the main spectrometer of solid crystalline or polycrystalline powder diffraction analysis due to its fast detection speed, easy operation, stability, good reproducibility, no need of focusing, less environment influence. But this type of instrument is rarely used in on-site rapid detection of drug/explosives at home and abroad because of its low resolution.By using energy dispersive X-ray spectrometer as its detection tool, this paper studies the new on-site portable rapid detecting method and key hardware and software technologies of practical instrument for the demand of the drug/explosive detection under complicated backgrounds. There are two research directions in this paper:detecting drugs hiding inside of human body and liquid dangerous materials such as liquid explosives, precursor chemicals and bums, etc. Although the energy dispersive X-ray detection instrument has many advantages, it belongs to weak light ray and has low resolution. When drugs are hidden inside of human body, energy scattering X-ray signal becomes weaker, and its resolution lower because of the body tissues’photon attenuation function and its complex structure, which makes it very difficult to accurately discern suspicious objects under test through traditional methods of looking for fingerprint peaks. In addition, the conventional X-ray method of detecting liquid dangerous materials is mainly through liquid density or the atomic number which normally only detect one-component liquid dangerous materials and raw materials while multi-component liquid dangerous materials are difficult to detect and identify through two-dimensional spectrum identification method. In order to solve this problem, it is necessary to apply intelligent algorithm to aide X-ray spectrum identification. The concrete research methods and routes of this paper are as follows:(1) Design and develop two kinds of energy dispersive X-ray detection equipments, respectively low energy detection experiment platform and high-energy multi-functional scattering experiment platform; explore the best condition of detecting drugs/explosives hidden in human body through studying the X-ray diffraction recognition law by detecting drugs/explosives in the human environment on detection platform; provide theoretical foundation for studying new detecting principles and methods of using X-ray energy dispersion to detect drugs/explosives; provide reliable data for the data processing and recognition of energy dispersive X-ray detection.(2) By using the energy dispersive X-ray spectrometer, this project studies the energy dispersive X-ray detection of drugs hidden in human body and its intelligent identification algorithm. Energy dispersive X-ray belongs to the weak X-ray beam, so energy dispersive X-ray detection’s energy resolution is lower than conventional small angle scattering X-ray in similar X light source energy case. Besides, the detection target of this project is drugs/explosives hidden in human body. It is very difficult to identify materials through materials’diffraction peak when the scattered signal of the material under test is rather weak after background causing attenuation effect on the light beam.Therefore, this project applies signal processing, pattern classification, statistical analysis and intelligent recognition and other algorithms to deal with the energy dispersive data obtained under complicated backgrounds. Using combinational algorithm of wavelet threshold and coherence function, we process the energy scattering X-ray data of heroin wrapped by different size and type of simulated human tissue (pork tissue). Through data denoising and coherence function matching, we establish simulated human tissue wrapped heroin’s energy scattering X-ray detection database, and then identify it. In order to study the identification rate of different drugs and similar matter wrapped by simulated human tissue, this project chooses seven materials wrapped by simulated human tissue (pork tissue) including TNT, phenylacetic acid, methamphetamine, heroin, piperonal, human body and salt as test materials, uses PCA algorithm to identify them, optimizes PCA algorithm through the neural network and studies the influence law of the principal component number extracted from PCA algorithm on the recognition rate;This project also chooses energy dispersive X-ray to detect drugs/explosives hidden in medical human body model, then adopts different pattern recognitions and statistical algorithms to process and recognize materials under test including TNT, phenylacetic acid, methamphetamine, heroin, piperonal, human body, and salt. The project puts forward a SVM classification algorithm based on particle swarm optimization. By the recognition and optimization of30sets of data of every material, we are seeking the optimal performance recognition algorithm of the SVM identification energy dispersive X-ray detecting drugs/explosives hidden in human body model. Furthermore, this project also studies a recognition algorithm of detecting drugs/explosives hidden in human body based on the discrete cosine transform and linear discriminant algorithm, and solves the problem of processing difficulty and low recognition of weak X-ray data by using this algorithm’s advantage of extraction and classification of high dimensional data’s decorrelation energy and feature.At the end of this chapter, we studies the edge fisher analysis detecting drugs/explosives hidden in human body, especially without any demand on sample distribution, uses geometric relationships between the adjacent samples to represent the properties of the sample distribution, better solves the identification and classification problem of weak X-ray data, and applies the method of K-near neighbor (KNN), support vector machine (SVM), combined algorithm of PCA, PCA+LDA and MFA to raise the recognition effect of TNT, phenylacetic acid, methamphetamine, heroin, piperonal, human body, salt hidden in human body.We research liquid dangerous materials’optical scattering characteristics under the detection of energy dispersive X-ray, choose the best test time, voltage, test angle, slit width etc. suitable for liquid dangerous materials, test common hazardous liquid sample, and get its3dimensional energy dispersive data. We build three-dimensional data model of liquid dangerous materials’energy-dispersive X-ray, regress, match and correct the load matrix’s multivariate data in the three-dimensional model, establish three-dimensional PARAFAC data model of liquid dangerous materials’ energy-dispersive X-ray, calculate the principal divisor number, then do the two-dimensional load matrix decomposition on the three-dimensional data model, classify and recognize the two-dimensional load matrix, and finally work out the accurate component and content of each material in the multi-component liquid explosive.To sum up, in view of the energy dispersive X-ray spectrum characteristics of drugs/explosives in (human body or human body model) under the complex background condition, this project adopts the energy dispersive X-ray detection method to respectively studies the statistical model, pattern classification, recognition algorithm, matrix analysis and other function algorithm. On the basis of analysis and detection of common drugs/explosives and liquid dangerous materials, the project puts forward a variety of effective detection methods which may hopefully provide technical support for developing new pattern energy dispersive X-ray detection instruments. |
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