Chinese Herbal Medicine Terahertz Spectroscopy

Terahertz (THz, 1THz=1012Hz) radiation with a frequency range of 0.1THz～10THz, sandwiched between microwave and infrared, belongs to far infrared region. In recent years, rapid progress in ultrafast laser technology provides a steady and available source for terahertz pulses generation, which greatly promotes the development of THz spectroscopy and imaging technique. This technique can record the amplitude of the wave by electro-optical or photoconductive sampling. After fast Fourier transform, the amplitude and phase of the THz pulse wave is given, then the refractive index and absorption of the material in THz region is extracted.The estimate and criterion of the quality of Chinese traditional medicine include three contents: security, authenticity and quality estimate. As well known, the curative effect of the Chinese traditional medicine is the result of its chemic component. Because of the complex chemic component, the quality estimate and control of Chinese traditional medicine is a difficult problem. This is also a primary factor of affects the traditional Chinese medicine modernization. The only way to resolve the problem is using external standard of quality estimate and date of experiment to prove the validity, stability and controllable of Chinese traditional medicine, enable the traditional Chinese medicine to occupy the small space in the international market. Many people have studied and explored the method of quality estimate of Chinese traditional medicine. The spectrum technology distinguishes Chinese traditional medicine according to its effective component, which can avoid the subjectivity and unilateralism. The spectroscopy could the more objective reflection raw material for medicine intrinsic quality is valued by people gradually. Among the spectroscopy, the infrared spectrum has been rapid developed. Using in the traditional Chinese medicine research, the THz radiation is to its effective supplement, beneficial attempt.Applied in Chinese traditional medicine's identification, THz radiation has some special advantages. 1) Some vibrational and rotational modes of Chinese traditional medicine's bimolecular are in THz region. 2) Dispersion spectroscope of Chinese traditional medicine is available in THz region, while not in infrared region. 3) Phase information is available as THz radiation is coherent. 4) With the pulse width of picosecond and femtosecond, THz radiation can be used to measure the time-domain spectroscope and transient characteristic of Chinese traditional medicine. The thesis's prime task was divided into two parts:First, the application THz pulse time-domain spectrum system regarding 6 groups of the traditional Chinese medicine which easy to confuse was conducted the spectrum experimental study. Each kind of the traditional Chinese medicine THz absorption spectrum and the data was obtained. They were carried on the preliminary distinction through observing and analyzing during its spectrum the difference, and the training data and the test data set were established for the BP neural network distinction and the recognition.Second, with using the BP neural network and based on the fractal theory, the traditional Chinese medicine was carried on the distinction. First, six groups traditional Chinese medicine which easy to confuse were carried on the appraisal and the recognition using the BP neural network, through changing the network's establishment, specially changing its concealment level the value, enhances its recognition effect. Finally, six groups traditional Chinese medicine majority were obtained the very good distinction. It provided an effective method in the identification for Chinese traditional medicines using THz time-domain Spectroscopy Technique. Second, based on the fractal theory THz spectrum recognition, the terahertz spectrums of two Chinese traditional medicines are obtained and their box counting dimensions are given and compared. The different medicines can be identified well in this way. This work achieves some basic research studies to the application of terahertz spectroscopy recognition technology; meanwhile, it carries on the certain extent discussion about the effect of the terahertz spectroscopy to the development of the traditional Chinese medicine.The chapters of the thesis were arranged as follows:Chapter one introduces the basic theories of THz spectroscopy technique, including the terahertz pulses generation, the terahertz pulses detection and its characteristics. Traditional methods of recognition of Chinese traditional medicines were summarized. Our major work and signification for this thesis were presented.In chapter two the principle of optical path which was built by our laboratory, experimental measurement procedure and sample preparation were presented in detail. Moreover, the chapter especially emphasized on the principle part which were used in the article, how to calculate optical constant of sample.Chapter three mainly introduced the artificial neural network development survey and the basic principle of the erroneous counter-biography neural network (BP neural network). BP neural network algorithm inferential reasoning and BP neural network principal characteristic and limitation.In chapter four, on the base of absorption spectra in the range from 0.2 to 2.6 THz of six groups Chinese traditional medicine using Terahertz time-domain spectroscopy technique, the THz absorption spectra of the six group Chinese traditional medicines were identified successfully by BP neural networks in the first time, through changing the network settings, specially changed the intermediate level the value, the most recognition rate reaches 100/%. The results indicate that it is feasible to apply BP neural network model on the identification of Chinese traditional medicine which easy to confuse and the traditional Chinese medicine which concocted differently, and providing an effective method in the identification for Chinese traditional medicines using THz time-domain Spectroscopy Technique.In chapter five, the basic concepts of fractal geometry and fractal box counting dimension are introduced. A new method of recognition of terahertz spectrum is suggested based on these concepts. The terahertz spectrums of two Chinese traditional medicines are obtained and their box counting dimensions are given and compared. The different medicines can be identified well in this way.Chapter six is the summary of my work including experimental results and pattern recognition. The future and hurdles of terahertz spectroscopy technique in the identification of Chinese traditional medicine were discussed.