Research On Measurement Technology Based On Terahertz Time-domain Spectroscopy And Imaging

Based on the commonly β-stimulants, flour additives and green tea, the detection of THz-TDS was thoroughly studied. Calculation of optical parameters of THz time domain spectroscopy was researched, the signal to noise ratio analysis of THz spectroscopy, the absorption source of spectrum of THz time domain spectroscopy was detail analyzed. Identification of substances by THz-TDS was theory researched and realized. THz-TDS imaging technology was thoroughly researched and compressed sensing was applied in THz spectroscopy. The main research and innovation were as follows.(1) The THz time-domain spectrums of four common β-stimulants were achieved, and then the absorption spectrums and refractive index spectrums of β-stimulants were calculated. This research provides a new approach for the detection of illegal using of P-stimulants in livestock and sports. The signal to noise ratio of the THz time domain spectroscopy was in-depth analyzed by Wavelet. Multi-layer decomposition and reconstruction of discrete wavelet, soft-threshold filtering and hard-threshold filtering of wavelet transform were applied respectively in THz time domain spectroscopy, and then the signal to noise ratio of the THz time domain spectroscopy was detail analyzed and improved. The solid density functional theory simulation and the molecular density functional theory simulation were applied respectively for explaining the source of the absorption peak in absorption spectrum. The vibration source were identified by theory calculated results and experiment results.(2)Based on the THz absorption spectra and refractive index spectrum of benzoyl peroxide and polyethylene mixture, benzoyl peroxide and flour mixture, regression analysis was applied. Wavelet filter, the first derivative and second-order derivative was applied in pretreatment. Wavelet filter, the first derivative and second-order derivative was applied in pretreatment of THz spectra. Regression analysis was carried out by algorithms of PLS and KPLS, and then the performance of the model were evaluated.(3) Multi-class classification and regression analysis based on THz spectroscopy was in-depth studied. Terahertz time-domain spectroscopy have been applied in research of four different varieties of chinese green tea, the absorption and refractive Terahertz Spectrum of these tea were got. Least Squares Support Vector Machines, Naive Bayes and Back Propagation Artificial Neural Network were applied to achieve Multi-class classification of these four kinds of tea, and the classification results of three algorithms were analyzed in detail. The PC control platform of THz-TDS system was developed by Visual C++. Based on the database of THz spectroscopy and principal component analysis algorithm, recognition functions were realized.(4) Simulation and experiment of THz-TDS imaging were carried out. Various THz imaging methods was tested, identify of different substances by THz imaging was achieved and3D imaging of THz time domain spectroscopy was realized. The application of compressed sensing in the THz time-domain spectroscopy and THz time domain spectroscopy imaging technology were researched. Based on the characteristics of the THz time domain spectroscopy and THz time domain spectroscopy imaging technology, various types of sparse base and various kinds of compressed sensing reconstruction algorithm were tested. Finally, signal to noise ratio of the spectra reconstructed by compressed sensing algorithms, the relative error, matching degrees and efficiency were evaluated. The application of compressed sensing in THz image deconvolution was researched. THz image deconvolution and noise removal were realized by GPSR compressed sensing algorithm, compared with the Wiener filtering and blind deconvolution, detailed analysis of its performance was carried out.