Research On High-transmittance Electromagnetic Shielding Method Based On Randomly Distributed Mirco-ring

In many valuable fields such as aerospace,communication and etc.,optical transparent elements' electromagnetic shielding technology has important application.The optical windows of many advanced precision photoelectric instruments need to have high transmittance and uniform stray light distribution at the same time to obtain excellent imaging quality and realize strong electromagnetic shielding to meet the comprehensive index of anti-interference ability of equipment.Among many kinds of high transmittance thin films,metallic mesh filtering technology is one of the effective methods to achieve high transmittance and strong electromagnetic shielding of optical windows,which can meet the balance between the indicators better.However,the existing metal grid structures are all designed according to a specific law,and gradually develop from simple structures to periodic structures with relatively complex periods.In this paper,based on the analyses and summaries of the different structural characteristics of existing metallic mesh,the relationship between the elements in the structure design and the transmission performance and electromagnetic shielding characteristics have been analyzed.On the basis of this,a structural design scheme of metallic mesh based on randomly distributed rings and sub-rings is proposed.The parameters of each basic-ring and sub-ring in the structure are random.Based on the scalar diffraction theory,the normalized diffraction intensity distribution model of metal mesh is established and the transmittance is calculated.Through simulation experiment,it can be seen that when the transmittance of metallic meshes are the same,the maximum diffraction intensity of metal mesh based on random-ring and sub-ring can be reduced by more than 75% compared with that of triangular ring array metallic mesh.In order to further optimize the diffraction characteristics of metal mesh,the generation method of metal mesh structure is optimized.After optimization,the maximum diffraction intensity of metal mesh based on random ring and sub-ring is reduced by at least 84% compared with that of triangular ring array metallic mesh.Based on the equivalent refractive index model of high-transmittance circular mesh and the structural characteristics of the metal mesh designed in this paper,the equivalent reactance model is modified to make it suitable for the analysis of electromagnetic shielding efficiency of metal mesh based on random ri ngs and sub-rings.Comparing with the results of CST UDIO SUITE software,the shielding efficiency deviation of metallic mesh in Ku band obtained by the modified equivalent refractive index method is less than 1 dB.Considering the diffraction and electromagnetic shielding characteristics of metal mesh comprehensively,the parameters of metallic mesh based on random rings and sub-rings are analyzed and optimized,including the number and radius of basic rings,the range of random values of basic ring parameters,the pattern of sub-rings,the number range of sub-rings,the wire width of metallic mesh and the filling mode of sub-rings.The simulation results show that the maximum diffraction intensity is reduced by at least 40% under the existing metallic mesh with the same transmittance.The metal mesh structure designed in this paper is processed by ultraviolet lithography technology,and the parameters of the metal mesh are tested by experiments.The experimental results show that the metal mesh samples base d on random rings and sub-rings can achieve high transmittance,depth homogenization of advanced diffraction and strong electromagnetic shielding efficiency at the same time.All the indicators are consistent with the simulation results,which prove the accuracy of the proposed diffraction model and electromagnetic shielding efficiency analysis model for random rings metallic mesh.The design method and sample of metal mesh structure proposed in this paper can meet the performance requirements of precision optical instruments and equipment,which has very impressive prospects to apply in aerospace and communications fields.