Mechanism Analysis And Researches On The Regulation Of The Absorbing Properties Of Absorbing Materials Tuned By Periodic Artificial Structures

With the improvement of modern information technology,the widespread use of electronic devices leads to the increasingly serious problem of electromagnetic radiation and electromagnetic interference.On the other hand,in the field of military and national defense,the signal detection technology of various countries has made rapid progress in recent years.Therefore,microwave absorbing materials or microwave absorbers,which play a key role in microwave stealth and electromagnetic shielding,are becoming a hot research topic.The traditional metal-based metamaterial microwave absorbers(MMPA)have the advantages such as ultra-thin,light weight and processing high absorption efficiency.However,the narrow absorption bandwidth and the discontinuous working frequency band hinder the application in actual needs.In order to broaden the bandwidth of metamaterial microwave absorbers,two kinds of broadband microwave absorbers using the design strategies of MMPA for reference are obtained by using graphite or carbonyl iron powder as the substitutes for metals in traditional microwave absorbers.In addition,we have systematically investigated the broadband mechanism of two new types broadband absorbers basing on the equivalent electromagnetic parameters and the field distribution mechanism of the artificial microstructures.The main work and innovations of this paper are as follows:1.Low metal surface resistance is the main reason for the narrow-band absorption mechanism of traditional metamaterial microwave absorbers.In order to effectively increase the surface impedance and broaden the bandwidth of the absorber,a graphite-based metamaterial absorber is designed by using graphite with low conductivity instead of copper.The regulation of the geometric parameters of graphite ring structure on the absorber's absorbing performance is systematically studied.The simulation and experimental results show that the optimized graphite-based metamaterial microwave absorber give rise to the absorption band from 12.7 GHz to 18 GHz(absorptivity ?90%).In addition,the graphite-based metamaterial microwave absorber is very sensitive to the thickness in graphite structure because the skin depth of graphite is much greater than that of metal.2.The magnetic carbonyl iron powder is a very common co ating absorbing material which has good microwave absorbing effects,large density and narrow-band absorption.In this paper,periodic square holes were excavated on the carbonyl iron plate,then the carbonyl iron plate was fabricated into a photonic cryst al plate structure.Moreover,we have systematically studied the regulations of geometric parameters of photonic crystal plate on its absorbing performance.The simulation and experimental results show that the optimized carbonyl iron powder photonic cryst al absorber can obtain an ultra-wide absorption band from 5.7 GHz to 20 GHz(reflection loss is less than-10 dB).This grid structure not only greatly broadens the absorption bandwidth,but also observably reduces the density of the microwave absorber(about a quarter of the carbonyl iron powder).