Study On The Orientation And Electromagnetic Properties Of The Microwave Absorbing Film

In real life,the electromagnetic wave pollution is increasingly serious,which makes the development of absorbing materials has attracted much attention.To improve the electromagnetic properties of absorbing materials is an important research content of new electromagnetic absorbing materials.According to the shape optimized Snoek equation,compared with other shapes of microwave absorbers,flake-shapes particles can achieve better magnetic properties.Studies have shown that the electromagnetic performance of the material can be further improved when the flake-shapes particles is oriented in the wave absorbing film.In this thesis,the microwave absorbing film materials were prepared by the tape casting process,and the research is carried out from the following two aspects:1.The variation law of the electromagnetic performance of the material when the flake-shapes particles is oriented inside the wave absorbing film;2.The influence of physical parameters on the orientation of the flake-shapes particles inside the microwave absorbing filmIn the first part we analyzed the electromagnetic performance of the oriented microwave absorbing film.Considering oriented and unoriented flake-shapes particles,respectively,the intrinsic permeability,the effective permeability and the Reflection Loss of the microwave absorbing film were calculated using the Landau– Lifshitz–Gilbert equation,Maxwell-Garnett’s effective medium theory and the Transmission Line Theory.The law of the electromagnetic parameters changing with the orientation angle is expounded.The calculation results demonstrate that the intrinsic magnetic permeability,effective magnetic permeability,and the reflection loss of the absorbing material are significantly improved when the flake-shaped particles is oriented uniformly.The electromagnetic properties of microwave absorbing flim can be effectively improved by controlling the orientation of flake-shaped particles.In the second part we studied the influence of the tape casting process parameters on the orientation of the flake-shapes particles inside the film.Aiming at the process of preparing the wave absorbing film by the tape casting,the relationship between the velocity profiles of slurry under the doctor blade and the orientation of the flake-shapes particles was analyzed using classical hydrodynamic equations,and a method was proposed to obtain the film with good orientation by eliminating the effect of the zero shear plane.The 3D model was estaslished to simulate the tape casting process and it was coupled with fluid simulation software Fluent and particle motion simulation software EDEM.The results demonstrate that by changing the physical parameters of the tape casting process and eliminating the effect of the zero-shear plane,the orientation of the particles in the tape casting film can be effectively improved,and the orientation state of the absorbing film can be controlled,which has a guiding role in actual production.Finally we carried out experiments to verify our simulation,the microwave absorbing films were prepared by using different tape casting process parameters,the particle orientation inside the composite material was observed with a Scanning Electron Microscope(SEM),and the electromagnetic parameters of the wave absorbing material were measured by a vector network analyzer(VNA).The results demonstrate that the microwave absorbing film material with the oriented flake-shaped particles has a greater advantage than the unoriented one in the electromagnetic performance.Through the mutual verification of the experimental results and coupling simulation results,the influence of the type casting process parameters on the motion state and orientation of the particles in the slurry is explained,and the problem of how to prepare a well-oriented microwave absorbing film material is solved.