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Porous plastics are used in various fields of industry, including radio- and electrotechnical fields. They are characterized by good heat- and sound isolating, dielectric and mechanical properties as well as by resistance to effect of various external factors during operation. The problem of estimation of effective permittivity of foam-polymer materials with a large volume fraction of pores, in particular, polyepoxide foam materials, has been considered. Two methods for solving it, both based on the matrix have been proposed. In the first method the matrix is considered as a polyepoxide binder, and the cavities filled with gas are taken as inclusions. In the second method the polyepoxide walls, separating cavities, are taken as inclusions, and gas filling cavities is considered as a matrix. To obtain the formulas for calculation, both methods use a generalized singular approximation of the theory of random fields. Based on the obtained expressions, the model calculations of the effective permittivity of a macroscopically isotropic foam material with a polymer binder based on E-20 and the cavities filled with freon, depending on the apparent density of the material, have been made. The calculations in the generalized singular approximations have been carried out for two of its variants: when the matrix was considered as a comparison medium; and, also by the self-consistent method. In the calculations using the second method two variants of the shape of the cells of the material have been considered: a weakly leaked or heavily leaked polyhedron. The calculated dependences obtained by all methods have shown the qualitative compliance with the experimental data.

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Syntactic materials (spheroplastics) having low density due to structural features, depending on the material of the microsphere walls can have a sufficiently high strength and low thermal conductivity, which makes them promising for use as heat insulation materials. By selecting the material of the microsphere walls and the concentration of the components of the spheroplastics, their dielectric characteristics can be significantly changed. In this work, the task of modeling the effective dielectric characteristics of a syntactic material with a polymer binder and filler in the form of hollow glass microspheres is considered, taking into account the presence of technological impurities in the material. A model for calculating the effective permittivity of a sample of a syntactic material was proposed, based on a model of a matrix composite with several types of inhomogeneous or homogeneous inclusions. To calculate, a generalized effective-field approximation for a heterogeneous medium with coated inclusions was used. Model calculations were carried out for syntactic foam with an organosilicon binder polydimethylsiloxane and hollow microspheres with E-glass shell with some moisture presence in the material. Frequency dielectric characteristics of this material were obtained in the range of 10-10 Hz. It has been shown that an increase in the volume fraction of hollow microspheres leads to a decrease in the dielectric constant and the tangent of the dielectric loss angle. It has also been shown that the calculated values are in satisfactory accordance with the experimental data obtained at an electromagnetic field frequency of 9.8 GHz.

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