Research And Application Of Equivalent Medium Theory Of Three-dimensional Composite Materials

With the development of materials research and manufacturing technology,three-dimensional composite materials have been more and more widely used in the field of electromagnetics.Although composite materials have many superior characteristics,due to the complex internal structure,it will cause electromagnetic modeling problems such as multi-scale and huge consumption of computing resources in practical engineering applications.Therefore,how to efficiently and accurately model and solve the electromagnetic problems related to composite materials has attracted much attention.The equivalent medium theory studied in this paper is one of the ways to solve the problem of electromagnetic modeling of composite materials.The basic idea is to replace the composite materials by simple homogeneous media,so as to simplify the electromagnetic modeling while ensuring that the external scattering characteristics of the material remain unchanged.The core of equivalent medium theory research is the extraction of equivalent parameters.In order to obtain accurate equivalent parameters,this paper first reviews the mixed formula equivalent method and equivalent method based on strong disturbance theory.These methods are mainly used in quasi-static situations where the wavelength is much greater than the internal unevenness of the material.Next,for composite materials with dispersion characteristics,this paper introduces three methods for obtaining equivalent electromagnetic parameters through S-parameter of infinite composite materials(S-parameter inversion method),namely free space method,4×4 matrix method and multi-angle S-parameter inversion method,after analyzing the advantages and disadvantages of these methods and optimizing them,oblique incidence S-parameter inversion method and improved 4×4 matrix method are proposed,and these methods are used to equivalence infinitely periodic honeycomb materials and frequency selective surfaces.At the same time,the phase unwrapping method is used to solve the multi-value problem that may be encountered in the process of extracting equivalent parameters from the multi-angle S-parameter inversion method.In order to verify the effectiveness and accuracy of the parameter extraction method,the S parameters of the model before and after equivalent are compared,and the results are very consistent.Finally,in order to verify the feasibility and applicability of the equivalent medium theory in practical engineering applications,the equivalent parameters extracted in the previous section are used to equivalently replace the limited-size composite plate,and the bistatic RCS of the materials before and after equivalent are compared.The comparison results show that the equivalent medium theory based on the S-parameter inversion methods is suitable for the equivalent replacement of honeycomb structure composite materials,but it is not completely applicable to the equivalent replacement of frequency selective surfaces in engineering applications.