Preliminary Study On Dielectric Fitting Of Human Skin And Subcutaneous Blood Glucose In Terahertz Band

Terahertz time domain spectroscopy(THz-TDS)technique has shown promising potentials in biomedical application,due to its special water sensitive,non-destructive,fingerprint spectrum characteristics.THz-TDS has been often used in property characterization of biochemical materials and in vivo experiments on human skin.However,on the one hand,there is still a lack of robust experimental protocol and data processing algorithm for in vivo THz experiments of human skin,and studies on simulation models of human skin in THz regime is also insufficient.On the other hand,it is difficult to characterize thin-film samples in THz-TDS experiments,so it is necessary to have further studies on the characterization methods and improve the characterization sensitivity for thin-film samples.In this thesis,a two-stage optimization method based on genetic algorithm is proposed for human skin dielectric fitting,and the double Debye models of human skin in different regions are established.At the same time,a multilayer reflection structure with high sensitivity is proposed to characterize glucose solutions with different concentration gradients.The main work and innovation written in this thesis can be concluded as follows:(1)Based on the electromagnetics theory and optics theory,the propagation mechanism of THz wave in media is analyzed,and the algorithms of experimental data processing and properties extraction for commonly used THz-TDS measurement models are derived,including the measurement models of bulk sample and thin-film sample in reflection THz-TDS,and the measurement models of bulk sample and thin-film sample in transmission THz-TDS.The theoretical basis of sample dielectric properties and optical properties extraction under THz-TDS experiments is studied and concluded.(2)The dielectric model of biological tissue in THz regime along with some common model fitting methods are studied.Then with the knowledge of genetic algorithm,a twostage optimized fitting method based on genetic algorithm is proposed,and the fitting accuracy of terahertz band double Debye model is compared.At the same time,in vivo THz experiments of human skin are carried out under reflection THz-TDS.The experimental protocol and data processing algorithm for in vivo THz experiments are given,and the double Debye models of three skin regions are established.(3)Characterization of thin-film liquid measured by THz-TDS is studied,and an algorithm is proposed for acquiring numerical solutions of complicated multilayer measurement models,which can extract THz optical properties stably and quickly.At the same time,an evaluation index is proposed for measuring the characterization sensitivity of THz measurement models,and the sensitivity of multilayer reflection structures with varied substrate materials and sample thicknesses is simulated and analyzed.Therefore,a window-sample-mirror structure with high characterization sensitivity is proposed,and the proposed structure is used to detect glucose solutions with 0 ? 20% mass concentration and 5% concentration gradient.Also,based on the effective medium theory,the theoretical model of refractive index of glucose solutions is established.