Research On Microwave Absorption Perforniance Of Broadband Radar-absorbing Materials

Based on the principle of impedance matching from transmission line theory, andelectromagnetic-wave loss mechanisms of radar-absorbing material, this dissertationmainly studied the loss characteristic and impedance matching characteristic ofmicrowave absorbing materials in the military frequently-used wave band of2-18GHz.In this dissertation the traditional ferromagnetic materials/ethylene propylenerubber (EPR) composite were synthesized, and the influences of the absorbing agentcontent on the microwave absorption properties have been studied; meanwhile thesingle layer absorber terminated by the metal aluminium (Al) was fabricated containingFe powders, effects of binders including varnish, putty and wax on the microwaveabsorbing performance have been investigated; finally this paper focused on thefabrication of La-doped strontium ferrite and the deposition of Ni on the surface ofcarbon nanotubes (CNTs) by chemical plating method. Through these modifications，thefactors that affect the absorbing properties were studied.The compositions of the microwave absorbing materials were examined usingenergy spectrum analysis (EDS), the crystal structures and morphologies werecharacterized using X-ray diffraction (XRD) and scanning electron microscope (SEM)respectively. Vector Network Analyzer was used to measure the electromagneticparameters and reflectivity of the microwave absorbing materials. Based on the databaseof electromagnetic parameters the reflectivity was calculated by Matlab software.The following conclusions have been obtained: with the absorbing agent content’sincrease from20%to60%, the microwave absorption performance of the traditionalferromagnetic materials/ethylene propylene rubber (EPR) was greatly enhanced, e.g.Fe/EPR, ferrite/EPR, the good microwave absorption property (the reflection lossR<-8dB) could be obtained at relatively high frequency (10-18GHz), and themicrowave absorption performance at low frequency was barely satisfactory; themicrowave absorbing property of Fe powders became poor after mixed with varnish orputty for their poor transmission characteristic, however, the absorbing peak moved tothe low frequency after mixing with wax in comparison with that of pure Fe powders;with the incorporation of La into strontium ferrite the real part of complex permittivitywas enlarged contributing to the lowering of the absorbing peak and the loss increase;the magnetic loss tangent of Ni-plated CNTs has been increased compared with that ofpure CNTs which contributed to the better attenuation characteristics.