Research On Preparation And Performance Of Composite Microwave Absorbing Structure

With the widespread application of electromagnetic wave technology in military and daily life,electromagnetic wave absorbing materials have become a necessary requirement for weaponry and other life electronic equipment,it is the current focus of attention and research at home and abroad.Large weight,narrow frequency band and high absorption peak are common problems in current absorbing materials,it is difficult to meet current practical applications and future needs,therefore,it is necessary to find a new type of absorbing material with light weight,bandwidth and low absorption peak.Based on the above purpose,this paper designs three different types of microwave absorbing materials,namely,frequency selective surface,absorbing coating and magnetic polyurethane foam,then the optimal parameters were selected to prepare the two-layer absorbing structure of magnetic polyurethane foam and the three-layer absorbing structure of three absorbing materials,and research its absorbing performance,the research content and conclusions of the paper mainly include the following three aspects:First,based on the basic theory of frequency selection surface,comsol simulation software is used to study the influencing factors such as unit structure size,dielectric layer parameters,layer spacing,incident angle and multi-level layer connection,etc,determine the optimal parameters and design a single-layer and double-layer frequency selection surface composed of a basic cross-shaped grid unit and an octagonal patch unit.After simulation analysis and verification,the double-layer frequency selection surface has two absorption peaks at 16.3GHz and 20.7GHz,reaching-56.5d B and-39.9d B respectively,and the absorption bandwidth at-10d B reaches 7.7GHz,which has a good angular stability,it meets the requirement of broadband frequency selection surface,and the double-layer structure is easier to process,which has important engineering significance.Second,characterize and test the microscopic morphology,composition and electromagnetic properties of the mixed ferrite selected in this article.At the same time,mixed ferrite is used as absorbent and epoxy resin is used as the matrix to prepare the absorbing coating on the aluminum substrate,the influence of coating thickness and absorbent content on the microwave absorbing performance of the coating is analyzed,the reflection loss of the coating decreases first and then increases with the increase of the coating thickness,but the coating thickness should not be too large according to actual requirements.The reflection loss of the coating gradually decreases with the increase of the absorbent content,when the absorbent content exceeds a certain threshold,the impedance between the coating and the atmosphere will not match,and the wave absorbing performance will become worse.When the mass ratio of the coating absorber to the substrate is 1:1,the absorption performance is the best,and the absorption peak at 15.2GHz reaches-12d B.Third,characterize and analyze the microscopic morphology,composition and absorbing mechanism of the magnetic polyurethane foam,and analyze the influence of factors such as the type of absorbent,the amount of absorbent and the foam density on the absorbing performance of the magnetic polyurethane foam,the results show that mixed ferrite has better absorbing effect than pure ferrite,the reflection loss of magnetic polyurethane foam decreases with the increase of density,when the density is 130kg/m~3,it has a larger filling ratio,and its reflection loss increases with absorption,the increase in the content of the absorbent showed a gradual decrease,when the density was300kg/m~3,the additive amount of the absorbent appeared a threshold,and the reflection loss first decreased and then increased with the increase of the absorbent content.At the same time,the absorbing performance of double-layer and triple-layer absorbing structures was prepared and tested.The two absorption peaks of the double-layer structure at 3GHz and 11.9GHz were-45d B and-14.6d B,respectively,and the absorption bandwidth with reflection loss at-10d B 4.8GHz;the three absorption peaks of the three-layer structure at 3GHz,10.5GHz and 24.5GHz are-29.6d B,-17.2d B and-11.3GHz respectively,and the absorption bandwidth at-10d B is 10.9GHz for the three-layer structure.The absorption bandwidth of the structure is wider than that of the double-layer structure,and the overall wave absorption performance is excellent,compared with a single absorbing material,the absorption peak of the double-layer and three-layer composite structure is reduced,the frequency band is broadened,and the absorbing performance is significantly improved.