Research On Testing Methods Of Absorbing Properties Of Absorbing Materials

With the rapid development of microwave engineering technology,new absorbing materials have been widely used in key areas such as defense industry,aerospace,and electronic information.In order to achieve effective absorption of incident electromagnetic waves,so that the reflection coefficient is sufficiently small and has sufficient electromagnetic properties such as resistive loss,dielectric loss,and magnetic loss.Special requirements for absorbing performance such as the reflection coefficient,absorbing bandwidth and center frequency of absorbing materials should be proposed.Therefore,exploring the non-destructive testing and evaluation methods for the absorbing performance of the absorbing materials has important guiding value for the absorbing material preparation process.Based on the electromagnetic wave reflection characteristics,a new method for characterizing the absorbing properties of absorbing materials is developed in this paper.The main contents include:(1)Using analytical method and equivalent wave impedance method to establish the theoretical reflection characteristics model of layered medium.Analyzing the relationship between the reflection coefficient and the frequency and angle of the normal-incidence and oblique-incidence electromagnetic waves at the boundary of single-layer / multi-layer absorbing media with or without substrate.The wave equation of electromagnetic waves is derived from Maxwell's equations.The wave equation harmonic solution is used to analyze the propagation characteristics and boundary conditions of electromagnetic waves in the layered medium,and the reflection coefficient of the layered medium is solved.(2)Simulation analysis is carried out to solve the reflection coefficient of the semiinfinite domain absorbing medium.In order to verify the correctness of the theoretical calculation,the frequency-domain solver in the CST simulation software is used to simulate the case where the plane electromagnetic wave is perpendicularly incident and obliquely incident on the single-layer / multi-layer absorbing medium with or without substrate.Set the boundary conditions and the angle of incidence,and calculate the reflection coefficient of the absorbing medium in the semi-infinite domain.(3)An electromagnetic wave reflection coefficient measurement system is established to carry out experimental research.Using vector network analyzer,coaxial line and horn antenna to construct microwave experimental measurement system to realize the experimental measurement of the electromagnetic wave reflection coefficient of the absorbing material at different frequencies;Carrying out experimental measurement research on absorbing materials with different volume ratio.The experimental results are compared with theoretical calculations and simulation results to verify the feasibility of using electromagnetic reflection coefficients to characterize the absorbing properties of absorbing materials.(4)Based on the reflection characteristics of electromagnetic waves,the absorbing properties of the absorbing materials are investigated.Taking the single-walled carbon nanotube / PEMA composite as the research object,the theoretical relationship model of the relative complex dielectric constant of the carbon nanotube / polymer composite and the carbon nanotube volume ratio and incident wave frequency is established.According to the theoretical expression of electromagnetic wave reflection characteristics,calculating the reflected wave-10 d B bandwidth change spectrum,the reflection coefficient change spectrum and the center frequency change spectrum in the frequency range of 1GHz-18 GHz and the angle range of 0 to 180 ° of incident electromagnetic wave,and then determine the pattern of-10 d B maximum absorption bandwidth,the minimum reflection coefficient,and the center frequency with the carbon nanotube volume percentage and thickness,incident wave angle and frequency changes.It lay a foundation for the processing preparation and performance testing of carbon nanotube / polymer composite materials in different engineering applications.