Research On Electromagnetic Protection Performance Characterization And Optimization Design Of Carbon Fiber Reinforced Plastics

The proportion of composite materials in modern electronic equipment and device shells and decorative parts is getting higher but their electrical properties are poor,and Carbon Fiber Reinforced Polymer Composite Material（CFRP）show uniaxial anisotropy characteristics,so electromagnetic compatibility is poor in equipment and systems.Studying the electromagnetic parameters of CFRP has a guiding significance for understanding the electromagnetic properties of the designed CFRP.In this subject,the multi-layer pressed carbon fiber composite board is used as the research object,and its electromagnetic parameter testing method is studied.In order to improve its electromagnetic compatibility protective performance,a conductive coating is applied.The main research work is as follows:（1）Firstly,the anisotropic electromagnetic parameter test method of CFRP is discussed.Based on the electrostatic field theory,the eigen equations of electromagnetic wave propagation in uniaxially anisotropic media are deduced,and the propagation and scattering of EM waves in uniaxially anisotropic media are simulated.The results show that in the X-band,when the electrical conductivity exhibits anisotropy,the uniaxial anisotropy or not of the permittivity have little effect on the transmission of electromagnetic waves.（2）Based on the resonator perturbation method,the structure size and feeding method of the cylindrical resonator were designed to test the uniaxial anisotropic permittivity tensor of the carbon fiber plate with the auxiliary waveguide transmission/reflection method.Firstly,the radius and height of the cavity are designed by studying the TE₁₁₂ mode of the cylindrical resonator.The results show that the insertion of the probe can eliminate the electric field in one direction and obtain the other one.The resonant frequency and quality factor of the cavity have no effect.After that,by studying the variation trend of the S-parameter at the resonant frequency and the polarization mode of the excitation electric field on the sample placement plane under the two feeding modes of the waveguide pinhole and the coaxial probe feeding,the design with A single-port reflective coaxial probe with obvious resonance characteristics is used to feed a cylindrical resonator to perturb a narrow-band TE₁₁₂ operating mode in the X-band.（3）The Al layer with about 40μm coated on the surface of the CFRP board by chemical aluminum plating,and the microscopic phase analysis and morphology observation of the carbon fiber thin layer structure before and after coating the metal layer were carried out.Based on the resonance-perturbation method,the permittivity component in the thickness direction of the CFRP board is tested using the designed cylindrical resonant cavity.The results of the permittivity tensor of the CFRP board prove that the permittivity of the CFRP board plane is higher than the thickness permittivity.And the surface of the CFRP board coated with a metal aluminum layer has effectively improved the DC surface conductivity and shielding efficiency.