Study On The Preparation Of Flexible Absorbing And Reflecting Electromagnetic Shielding Composites By SCFNA Method

Traditional metal shields are not suitable to use in production and living because of their high metal content and lack of flexibility.Conductive polymer matrix composites are effective substitutes for thin metal plates and wire mesh,and can provide effective electromagnetic shielding.For conductive polymer matrix composites,the substrate itself is insulated,and when conductive fillers larger than the conductivity threshold are processed to the matrix,the composite will conduct electricity,thus realizing the shielding function.In this thesis,polydimethylsiloxane(PDMS)was used as the matrix and chopped carbon fiber(SCF)was used as the filler.It mainly studied the preparation of PDMS/SCF flexible electromagnetic shielding materials based on the SCFNA method.The main research contents are as follows:(1)The effects of early hybrid technology on the network construction and electromagnetic shielding performance and mechanical properties of PDMS/SCF composite materials were studied.When the mixing speed was constant,the average shielding efficiency at 210s was 53.38%higher than that at 600s.When the mixing time was constant,the average shielding efficiency at 1800r/min was 52.48%higher than that at 2200r/min.Combined with the effects of mixing time and speed for PDMS/SCF composites on electromagnetic shielding performance and mechanical properties,and the optimal process conditions were determined.(2)The shielding performance the PDMS/SCF composites were tested by the waveguide method.The experimental results showed that in a certain range,PDMS/SCF composites are mainly composed of absorption loss,and the proportion of absorption loss in the total shielding efficiency increased gradually with the increase of electrical conductivity(3)The X-band rectangular waveguide model was established in the HFSS software,and the effect of composite material conductivity,filler content and material thickness on the shielding effect was simulated by setting the material properties,boundary condition and excitation.The HFSS simulation results showed that the electrical conductivity of the material can enhance the shielding effectiveness.When the conductivity was within a certain range,the shielding effectiveness of the material was mainly based on the absorption efficiency;when the conductivity reached the metal level,almost 100%of the shielding effectiveness was caused by reflection loss,which will cause secondary electromagnetic interference.(4)Compared to the measured data of the waveguide method,HFSS program simulation data and calculated theoretical values,and the frequency range was from 8.2GHz to 12.4GHz.The comparison showed that the difference between the HFSS simulation data and the experimental results is relatively small,which proves that the HFSS simulation simulation has higher accuracy in predicting the law of material shielding effectiveness.(5)The possible shielding applications of PDMS/SCF films were studied.A simplified model was established in HFSS software and simulated.The simulation results showed that the thickness of PDMS/SCF film was constant and the SCF content was 0%-10%wt,the average SAR value decreased from 75mW/g to 0.9mW/g,and the maximum reduction was 98.86%.In the frequency of 8.2GHz,9GHz,10GHz,11GHz,12.4GHz,through the comparison of the intracranial electric field strength with and without protective materials.It was found that the electric field intensitywith protective materials was weakened by about 90%,which highly reduced the intracranial electric field strength.The results showed that PDMS/SCF films have a strong ability to shield external microwaves.