Effective Nonlinear Response To External AC Electric Field In A Kind Of Graded Coated Composites

Composite dielectric materials are a new type of materials, which are constituted by the reorganizations of two or more kind of the single component materials with different properties through physical or chemical means. They can keep the advantages of all kinds of single component materials , overcome their defects and expand the application range of the materials. Now people make their comprehensive performances be better than th at of the original component materials to deal with a variety of different needs. The research of the characteristics of composite dielectric materials has always been a hot issue for scientists, and its properties and applications of optical and magnetic are given more care and attention by physicists. A kind of nonlinear composites, where the granular inclusions are randomly embedded in the host, plays a significant role in engineering applications. For this type of nonlinear composites, an external electric field will have a significant impact on the effective nonlinear response. Under the action of different external electric fields, the effective responses are also different. Therefore, it is very important to research the response of the composites.In this thesis, by using the perturbation method, the effective nonlinear AC response of the nonlinear composite is investigated under the action of an external AC electric field E_a =E₁ sin??w? + E3 sin?3?t?, where the cylindrical gradient coated inclusion and spherical gradient coated inclusion are randomly embedded in a host medium respectively. The local potential distributions of composites are derived in the inclusion core, the coated layer and the host regions, and all the effective nonlinear AC responses of the composites and their relationships are obtained in a dilute limit.The main contents are as follows:1.A brief summary of the research background, the present status for effective AC response of the composites and the research work of this thesis are given;2. By using the perturbation method, effective nonlinear AC response of the nonlinear composites, which is formed by spherical inclusions with gradient coatings and cylindrical inclusions with gradient coatings randomly embedded in a host medium, is investigated under the action of an external AC electric field E_a = E₁ sin??t? + E3 sin?3?t? . The electric potential distributions of two types of composites are given in the inclusion region, coated region and host region,respectively;3. All the effective nonlinear AC responses of the nonlinear composites are obtained at the fundamental frequency and third order harmonic frequency in a dilute limit. Moreover, the relationship between the nonlinear effective response at the fundamental frequency and third harmonic frequency are also given;4. The research results of this thesis are summarized and discussed, and the outlook for further work is pointed out.