Neural Network To Identify Drugs And Antibiotics Terahertz Spectroscopy

The terahertz (THz, 10¹² Hz) wave, categorized between millimeter radio waves and far infrared light wave, with a frequency lying in 0.1 THz and 10THz, belongs to far-infrared band (wavelengths 30 μ mto 3mm). Since it possesses many attractive characteristic properties, the studies of its applications have caused more and more attentions. It is believed that THz technique has a good future in many different fields, such as physics, chemistry, biological medicine, communication, radar, security inspection, etc. In recent years, rapid progress in ultrafast laser technology provides a steady and reliable source for the THz pulses generation, which greatly promotes the research in the THz waveband that is difficult to access before. This thesis, based on THz spectrum technique, a frontier subject, mainly focused on spectrum applications and identification arithmetic.The main work of this thesis was proposed in chapter three and chapter four.In chapter three and four, on the base of absorption spectra in the range from 0.2 to 2.6 THz of nine illicit drugs and six antibiotics using Terahertz time-domain spectroscopy technique, the THz absorption spectra of nine different illicit drugs and six antibiotics were identified successfully by BP neural networks. The model of BP neural network were processed in Matlab. The results indicate that it is feasible to apply BP neural network model on the identification of illicit drugs and antibiotics, and providing an effective method in the secure inspection and identification for illicit drugs and western medicine using THz time-domain spectroscopy technique.In chapter five, six antibiotics were studied by the terahertz time-domain spectroscopy technique. Twenty four absorption spectra of the six antibiotics, each of them has four spectra, were obtained. The twenty four absorption spectra can be clustered using Self-Organizing feature Map (SOM) network. The results indicated that SOM network would be another powerful method in the classification of illicit drugs and antibiotics.In chapter six, illicit drugs prepared as different state (powder or tablet) were detected using terahertz time-domain spectroscopy technique and the spectral absorption in terahertz region was obtained. From the results, we concluded that different sample state (powder or tablet) has almost no influence on experimental data by contrasting and analyzing their spectral absorptions. This result will guarantee the feasibility and validity of the existing sample preparation methods.The investigation is the first step for detection and non-destructive inspection of illicit drugs. At the same time, two street drugs were detected using terahertz time-domain spectroscopy technique and the result was discussed.In the other chapters, chapter 1 was the introduction of this thesis. Chapter2 introduced the arithmetic of BP network and SOM network. Chapter7 was the summary of this thesis.