太赫兹波段生物组织介电特性数值模拟研究

发布时间：2018-05-20 20:15

本文选题：太赫兹 + 介电特性　；参考：《兰州交通大学》2015年硕士论文

【摘要】：太赫兹波对生物组织基本没有伤害,并且具有较好的穿透能力。当太赫兹射线用于监测生物组织、分析其结构和组成时,可以克服常用的可见光或紫外光对生物组织进行分析时信号弱、图像模糊等问题。太赫兹频段生物组织介电特性的研究具有重要医学应用价值,但很多生物组织在太赫兹波段的介电特性是未知的。本课题对描述生物组织在太赫兹频段的介电特性的模型进行了研究,包含如下内容:(1)简单介绍了太赫兹的产生探测以及时域光谱技术等。详细阐述了电介质的微观极化机制、极化的宏观描述、生物组织弛豫和色散特性、双德拜模型和Cole-Cole模型。(2)德拜模型能描述皮肤组织太赫兹波段的介电特性,由于非线性最小二乘法的传统算法在提取德拜模型参数时,对参数初始值要求高,所得模型与原始数据偏差较大。将遗传算法应用于非线性最小二乘法对原始数据进行拟合,并提取参数。将遗传算法应用于非线性最小二乘法提取参数时无需设置初始值并且减小了文献中模型在0.15THz-0.6THz频段与原始数据的偏差。验证了遗传算法提取德拜参数的有效性和皮肤组织太赫兹波段德拜模型的正确性。(3)生物组织在低频段的介电特性有大量的实验数据,并且四阶Cole-Cole模型能描述生物组织在10Hz-100GHz频段的介电特性。为了获得生物组织在太赫兹波段的相对介电常数和电导率,在四阶Cole-Cole模型基础上进行修正,使修正后的模型不仅能描述生物组织在10Hz-100GHz频段的介电特性,还能描述生物组织在太赫兹波段的介电特性。在四阶Cole-Cole模型上新增了一项?ki对正常皮肤组织在10Hz-20GHz和0.15THz-1.95THz频段的介电特性的实验数据按照文献方法进行处理,提取四阶Cole-Cole修正模型的参数。在10Hz-100GHz频段内原有模型和修正模型计算值的相对误差在5%以内,并且在太赫兹波段正常皮肤组织修正模型的相对介电常数和电导率的计算值与实验数据的相对误差基本在10%以内,结果验证了四阶Cole-Cole修正模型的正确性。将该修正模型应用在脑组织太赫兹波段的介电特性的计算中,得到了脑白质和脑灰质在0.15THz-1.95THz频段的相对介电常数和电导率。所提出的四阶Cole-Cole修正模型可用于对其他生物组织在太赫兹波段的介电特性进行预测。
[Abstract]:Terahertz wave has little damage to biological tissue and has good penetration ability. When terahertz rays are used to monitor biological tissues and analyze their structure and composition, the problems such as weak signals and blurred images can be overcome in the analysis of biological tissues by visible or ultraviolet light. The study of dielectric properties of biological tissues in terahertz band has important medical application value, but the dielectric properties of many biological tissues in terahertz band are unknown. In this paper, a model describing the dielectric properties of biological tissues at terahertz is studied, including the following contents: 1) the generation detection and time-domain spectroscopy of terahertz are briefly introduced. The microscopic polarization mechanism of dielectric, the macroscopic description of polarization, the relaxation and dispersion characteristics of biological tissue, the double Debye model and the Cole-Cole model. 2) Debye model can describe the dielectric properties of the skin tissue in terahertz band. Because the traditional nonlinear least square algorithm requires high initial values of the Debye model parameters, the deviation between the model and the original data is large. Genetic algorithm is applied to fitting the original data by nonlinear least square method and extracting parameters. The genetic algorithm is applied to the nonlinear least square method to extract the parameters without setting the initial value and to reduce the deviation between the model and the original data in the 0.15THz-0.6THz band in the literature. The validity of genetic algorithm in extracting Debye parameters and the correctness of THz Debye model in skin tissue are verified. And the fourth order Cole-Cole model can describe the dielectric properties of biological tissues in the 10Hz-100GHz band. In order to obtain the relative dielectric constant and conductivity of biological tissue in terahertz band, the modified model is modified on the basis of fourth-order Cole-Cole model. The modified model can not only describe the dielectric properties of biological tissue in the 10Hz-100GHz band. It can also describe the dielectric properties of biological tissues in terahertz band. An experimental data of dielectric properties of normal skin tissues in 10Hz-20GHz and 0.15THz-1.95THz bands was added to the fourth-order Cole-Cole model, and the parameters of the four-order Cole-Cole modified model were extracted according to the literature method. The relative error between the original model and the modified model in the 10Hz-100GHz band is less than 5%, and the relative error between the calculated values of the modified model and the experimental data in the terahertz band is within 10%. The results show that the fourth order Cole-Cole modified model is correct. The modified model is applied to calculate the dielectric properties of brain tissue in terahertz band. The relative permittivity and conductivity of white matter and gray matter in 0.15THz-1.95THz band are obtained. The proposed four-order Cole-Cole modified model can be used to predict the dielectric properties of other biological tissues in terahertz band.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：Q6-33;O441.4

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