两相介质混合物电磁色散特性的准动态均一化技术及应用

Conventional homogeneous model and the related classic retrieval methods based on scattering parameters (S-parameter retrieval) have been demonstrated to be insufficient and even inaccurate to depict the dispersive macroscopic electromagnetic properties of a given composite sample. Based on our previous studies and informative results, this project aims to propose novel homogenization models and relevant homogenization techniques (particularly S-parameter retrieval methods) in quasi-dynamic region for a series of bi-phase dielectric composites with finite thickness. The models to be presented enclose anisotropic model, stratified model, stratified model with anisotropic boundary layers, and bi-anisotropic model, respectively. For each proposed homogenization model, the corresponding S-parameter retrieval methods will be deduced to determine its characteristic parameters. Hopefully, positive results can then confirm that the introduced homogenization model and S-parameter retrieval methods are capable of characterizing the dispersive macroscopic electromagnetic properties of dielectric composites in a broader frequency range, and therefore, provide a potential technique to measure in practice the macroscopic electromagnetic dispersion of a given material sample. One the other hand, based on the abovementioned homogenization results, this project will quantify the quasi-static limit for the bi-phase dielectric composites. Commonly, scientific researchers define this important limit qualitatively as that the ratio between smallest heterogeneity and effective wavelength inside the composite of interest should be far smaller than unity. According to our best knowledge, such a quantification attempt has not been reported in literature. This complicated yet important study will possibly facilitate us to determine whether it is appropriate to apply conventional homogenization theories to explain the operation mechanism, and to further improve the design approaches of recently-appeared materials with electromagnetic properties not easily observed in nature.

传统的均匀物质模型和传统的散射参数逆推法在准动态频域内已经无法正确的描述混合物的宏观电磁色散特性。在前期工作的基础上，本项目拟针对薄板型两相介质混合物提出新型准动态电磁均一化模型以及相应的均一化技术，特别是散射参数逆推法。拟引入的新型均一化模型包括各向异性模型、层式模型、带有各向异性边界层的层式模型和双各向异性模型。并针对每种均一化模型提出了不同的均一化方法（即散射参数逆推法）用以确定相应模型的特性参数。以期进一步拓宽准动态电磁均一化理论的可用频率范围，为实际测定电磁媒质的宏观电磁色散特性提供可行的技术手段。在此基础上，本课题拟针对薄板型两相介质混合物量化其准静态边界。一直以来，科研工作者只定性的描述准静态边界，而如何量化这一边界目前尚未见报道。这项研究将为能否利用传统电磁均一化理论解释新型电磁材料的工作机理，进而改进和拓展新型电磁材料的设计方法提供重要的理论依据。

传统的均匀物质模型和散射参数逆推法在准动态频域内已无法正确描述混合物的宏观电磁色散特性，所得到均一化模型参数常常会违背基本的物理定律，如无源定律和因果定律。. 本项目开展了以下四个方面的研究内容：第一，针对薄板型两相介质混合物提出了新型电磁均一化模型，并在平面电磁波垂直入射的条件下推导出相应的基于散射参数逆推法以确定模型的特性参数；第二，推导出适用于以任意角度入射的平面电磁波激励条件下的散射参数法，进而验证单个均一化模型的电磁特性参数是否与入射角度相关；第三，讨论混合物的等效厚度对于均一化模型特性参数的影响；第四，利用电磁均一化结果，针对薄板型两相介质混合物，量化其准静态边界。 . 我们将研究成果归纳为以下三个方面。第一，提出了四种新型均一化模型包括各向同性模型、各向异性模型、层式模型和带有各向异性边界层的层式模型。针对每种模型推导了不同的均一化方法（即散射参数逆推法）用以确定相应模型的特性参数。研究结果表明模型越复杂，其可用频率范围越宽，与传统均匀模型相比，可用频率范围最多拓宽了86%；第二，将上述四种散射参数法推广到适用于平面电磁波斜入射的条件。并发现模型越复杂，模型特性参数对于不同电磁激励的响应差别越小。达到了进一步拓宽准动态电磁均一化理论的可用频率范围的目的，为实际测定电磁媒质的宏观电磁色散特性提供可行的技术手段；第三，提出了一种在不同频点确定相应模型等效厚度的自适应算法，有效解决了逆推过程中等效厚度难以界定的问题，并成功消除了法布里佩罗谐振对于逆推结果的负面影响。并针对薄板型两相介质混合物，确定了量化其准静态边界的步骤，得到了准静态边界关于内含物体积填充率和介电常数的函数表达式。结果表明随着内含物体积和介电常数的增加，混合物的准静态边界逐渐降低。本项目的研究成果为能否利用传统电磁均一化理论解释新型电磁材料的工作机理，进而改进和拓展新型电磁材料的设计方法提供重要的理论依据。