DESIGN OF ELECTROMAGNETIC SCREENS OF GUARANTEED EFFICIENCY FOR CIVIL SECURITY AND ELECTROMAGNETIC COMPATIBILITY

Abstract

The principles of designing composite materials with guaranteed (required) efficiency are considered. The main ratios for evaluating the efficiency of the designed material are given. The main condition for obtaining a material with low reflection coefficients of electromagnetic waves is the approximation of the wave resistance of the surface layer to the air resistance. Calculations showed that in order to ensure a minimally acceptable reflection coefficient (0.25–0.30) and sufficient absorption coefficients of electromagnetic energy (-20 dB in power), the material should be multi-layered with a middle layer of high absorption properties. This is ensured by its high electrical conductivity. A possible option is a monotonous increase in electrophysical properties from the outer surface to the inner one. If it is necessary to simultaneously shield the electromagnetic field of ultra-high and higher frequencies and the magnetic field of ultra-low frequencies (industrial and its harmonics and interharmonics), the material must contain a magnetic filler. Its volumetric amount is determined by Odelevsky's formula. The reflection coefficient in this case is determined by the ratio of the absolute magnetic and dielectric permeabilities of the surface layer. To simplify the design of the material, the ferromagnetic particles of the filler should be electrically insulated. At the same time, the radio-absorbing material (or material layer) must have branched conduction circles in the structure. In the process of designing the material, when choosing the matrix, it is mandatory to take into account not only the dielectric constants of the materials, but also the tangents of the dielectric loss angles.