Research On Transparent Electromagnetic Shielding Method Based On Graphene Stacked Structure

Viewing window with high-performance of electromagnetic shielding has become increasingly urgent required for advanced equipment,electronic communications and aerospace.Its performance requires are concentrated as follow: maintaining good optical visibility,achieving high-level electromagnetic shielding,and reducing secondary pollution caused by electromagnetic reflection.Graphene has optical transmittance and partial microwave absorption characteristics,shows great application potential in the field of transparent electromagnetic shielding.However,there are still several problems restrict the applicantion of graphene based transparent electromagnetic shielding technique,such as low electromagnetic shielding effectiveness,the constraint of optical transmittance and microwave absorbing ability,and so on.In view of the above problems,graphene and its composite structures with transparent dielectric and metal mesh were taken as the research objects.The factors and mechanisms affecting microwave absorbing capacity of graphene/transparent dielectric stacked structures were analyzed by modeling their microwave transmission characteristics.The effects on electromagnetic shielding ability of different combinations of metal mesh and graphene were studied.And then,the transparent electromagnetic shielding methods based on graphene/transparent dielectric stacked structure,graphene/metal mesh composite conductive film,and graphene/transparent dielectric/metal mesh stacked structure were proposed for different application needs aiming at achieving high visible transmittance,low electromagnetic reflection,and strong electromagnetic shielding.The results were verified by experiments.The specific research content is as follows:In order to solve the problem of no systematic analysis model for microwave transmission properties of multilayer graphene,a microwave transmission characteristic analysis model of graphene was established based on Kubo formula,boundary conditions of electromagnetic field and Maxwell's equations.The analysis shows that the difference between the dielectric loss tangent and the magnetic loss tangent increases,that is,the impedance matching is weakened as the number of graphene layers increases,resulting in electromagnetic shielding mechanism of graphene changed,which is dominated by absorption for single layer and reflection for multilayer.This provides a theoretical basis for the design of graphene based transparent electromagnetic shielding devices.In order to achieve high visible transmittance and strong microwave absorbing capability,a transparent microwave absorbing method based on a graphene/transparent dielectric stacked structure was proposed.Single-layer graphene and transparent dielectric were alternately arranged to form a stacked structure.The model for analyzing microwave transmission characteristics was established.The analysis shows that due to the Fabry-Perot effect,the stacked structure exhibits multiple absorbing resonance peaks characteristics,and the microwave absorbing capability can be effectively improved while maintaining high optical transmittancy by optimizing the thickness of the dielectric.The experimental results show that compared with multi-layer graphene,the microwave absorbance of the multi-layer graphene/transparent dielectric stacked structure was increased by more than 60%;the four-layer graphene/transparent dielectric stacked structure sample can achieve microwave absorbance of 87% and visible transmittance of 90% at the same time.In order to alleviate the inherent contradiction between visible transmittance and electromagnetic shielding effectiveness,a transparent electromagnetic shielding method based on graphene/metal mesh composite conductive film was proposed.Based on the boundary conditions and the Shacklette model,the analysis indicates that electromagnetic shielding effectiveness is negatively correlated with the sheet resistance of graphene.The equivalent impedance model based on the transmission line was established.The analysis shows that the sheet resistance of the composite conductive film consisted by graphene and metal mesh is significantly smaller than that of graphene,and thus the electromagnetic shielding effectiveness can be improved.Experiments show that the sheet resistance of the graphene/metal mesh composite conductive film was 1/40 of that of graphene.Compared with double-layer graphene which showing the same visible transmittance of 94%,the electromagnetic shielding effectiveness of the graphene/metal mesh composite conductive film was improved by 14.41 dB.In order to solve the problem that the existing transparent electromagnetic shielding technology cannot simultaneously achieve high visble transmittance,low electromagnetic reflection and strong electromagnetic shielding performance,a transparent electromagnetic shielding method based on graphene/transparent dielectric/metal mesh stacked structure was proposed.The method using transparent dielectric/metal mesh as reflecting layer,transparent dielectric/graphene setting in the direction of microwave incidence as absorbing layer to form a stacked structure.Based on transmission line theory and equivalent impedance theory,the model of microwave transmission characteristics was established.The analysis shows that the stacked structure utilizes metal mesh to achieve strong electromagnetic shielding.The contribution of graphene/transparent dielectirc to the stacked structure was analyzed through CST electromagnetic field simulation software,indicating that the incident microwave is strongly absorbed due to passing through the absorbing layer many times;and optical wave passes through the stacked structure only once to achieve high visible transmittance.Experiments showed that the proposed stacked structure based on double-layer graphene and double-layer metal mesh can simultaneously achieve visble transmittance of 91%,the electromagnetic shielding effectiveness of Ku-band better than 35 dB,and the mainly electromagnetic shielding mechanism was absorption.The study solved the existing transparent electromagnetic shielding technique cannot achieve high visible transparency,low electromagnetic reflection and strong electromagnetic shielding at the same time,and laid the foundation for transparent electromagnetic shielding applications of graphene in high-end equipment,electronic communications and other fields.