Simulation of the Propagation of Electromagnetic Waves in Radio-Absorbing Ni‒Zn Ferrites

Nickel‒zinc (Ni‒Zn) and magnesium‒zinc ferrites (Mg‒Zn) and composites based on them are among the most promising radio-absorbing materials that can effectively absorb electromagnetic radiation in the frequency range from several megahertz to several gigahertz. Many questions related to the radio-absorbing properties of these materials still remain open due to the influence of the parameters of a sample on both the frequency dependences of permittivity and on the parameters of domain walls. In this study, a mathematical model of the propagation of electromagnetic waves in radio-absorbing Ni‒Zn ferrites is proposed. The boundary and initial conditions that take into account the geometry and microstructure of the samples are established. The solution of the formulated boundary value problem on a segment using the method of separation of variables or the Fourier method showed that the amplitude of an electromagnetic wave decreases significantly after passing through half the sample thickness, which points out the high radio-absorbing performances of the investigated Ni‒Zn ferrites. The reflection of a plane polarized wave from a Ni‒Zn ferrite/metal plate bilayer in the frequency range of 1–1000 MHz is numerically analyzed. The results of the simulation are verified by the experimental data on the radio-absorbing properties of 1000NN Ni‒Zn ferrites. It is shown that the assumption about the exponential nature of the dependences of the permittivity and permeability on the normalized coordinate is only applicable in a narrow frequency range of up to 3 MHz, in which the experimental and numerical data are in good agreement.