Research On Transparent Frequency Selective Surfaces Based On Triangular/Orthogonal Micro-ring Metallic Meshes

The electromagnetic shielding transparent optical components have important application value in the fields of aerospace equipment,communication facilities and advanced optical instruments.The ultimate goal is to achieve high transmittance,strong low-frequency electromagnetic shielding effectiveness and uniform stray light distribution simultaneously.Optically transparent frequency selective surface(FSS)is required to achieve frequency selectivity in the shielding band based on the above performance.The indicators include four aspects,excellent passband performance,strong low-frequency electromagnetic shielding effectiveness,high transmittance and uniform high-order diffracted light intensity distribution namely.However,it is difficult to balance the various indicators above.In this thesis,a metallic mesh structure with equilateral triangle and two-dimensional orthogonally arranged circle and inside sub-rings was proposed.The scalar diffraction theory and the angle spectrum theory was applied to establish the normalized diffraction intensity distribution model.The equivalent reactance model was corrected in order to fit the above structure.In consideration of the optical and electromagnetic characteristics,the structural parameters such as sub-ring arrangement,sub-ring rotation rules,number of sub-rings,substrate thickness and double-layer interlaced angle were optimized.The proposed structure was used in meshed FSS in order to improve light transmittance.In addition,the electromagnetic transmission characteristics of double-layer hexagonal FSS were studied through CST STUDIO SUITE.How the structure parameters such as side length,ring width,array period,double-layer gap,and double-layer interlaced angle affect indicators such as center frequency,3d B bandwidth,passband transmittance was studied.Taking the processing technology and experimental test requirements into consideration,the parameters were selected.The metal part of the double-layer hexagonal FSS was meshed with the proposed structure and the simulation analysis and parameter optimization were performed respectively.The simulation results showed that the light transmittance of the obtained double-layer metallic mesh was about 95%,the maximum high-order diffracted light intensity was reduced by over 90% compared with orthogonal circle metallic mesh,and its electromagnetic shielding effectiveness averaged over 30 d B in 12 to 18 GHz band.The meshed FSS maintained the frequency selection characteristics,and had got a significantly enhance in light transmittance,and the stray light distribution was more uniform.Samples with the designed parameters had been fabricated by UV lithography,and experimental testings were performed.Experimenal results demonstrate that the obtained double-layer metallic mesh sample achieved high light transmittance,strong electromagnetic shielding,and low imaging quality impaction simultaneously.The light transmission of meshed FSS also increased from 1% to 90%,and a uniform stray light distribution was achieved on the basis of maintaining the original electromagnetic transmission characteristics.Its frequency selection characteristics were significantly better than the commonly used single-layer structure,so that high light transmittance,excellent passband characteristics,and low imaging quality impaction were achieved.The metallic mesh and meshed FSS can be applied to light window on area of optically transparent electromagnetic shielding such as aerospace equipment,precision optoelectronic devices,etc.