| Electromagnetic shielding fabric has the advantages of softness,light weight and high strength,and is widely used in electromagnetic compatibility and electromagnetic protection fields.At present,the design and performance analysis of electromagnetic shielding fabrics are mainly based on designers’ past experience and reference to similar fabrics,which has a long development cycle and high investment cost.In recent years,with the rapid development of electromagnetic field numerical simulation technology,the numerical simulation of shielding efficiency based on the testing principle of shielding chamber window method has become an important means to study the shielding properties of fabrics.Compared with the shield chamber window method,flange coaxial method is more widely used in practical production and research because of its lower testing cost and simpler operation.Therefore,based on the testing principle of material shielding efficiency of flanged coaxial method,a simulation model of fabric shielding efficiency was established in this paper,and the rapid and accurate prediction of fabric shielding performance was realized through computer numerical simulation.The paper takes the silver-coated polyester filament fabric with the same density of warp and weft as the research object,and combines the actual spatial structure of the fabric to construct the three-dimensional meso model and the simplified model respectively.According to the principle of flange coaxial test,a fabric shielding efficiency simulation model in 30-1500 MHz band was established by using CST microwave studio software.The fabric shielding efficiency simulation model was used to solve and calculate the constructed fabric model,and the advantages and applicability of three-dimensional fabric mesoscopic model and simplified model in fabric shielding performance simulation were compared.The results show that the electromagnetic field distribution of the simulation model is consistent with that of the actual test,the voltage standing wave ratio is less than 1.2,the transmission loss is less than 1 d B,and the transmission performance of the model meets the technical requirements of the flange coaxial device in the standard GJB6190-2008 "Testing Method for the Shielding Efficiency of Electromagnetic Shielding Materials".In Figure B-A,the data points in the 95% consistency interval between the experimental results of fabric shielding efficiency and the simulation results based on fabric 3D model and simplified model are 96% and 95% respectively,indicating that the simulation model has a good consistency between the simulation results and the test results of the shielding efficiency of the two fabric models.In addition,the average difference rate of less than 3% between simulation and test results proves that the simulation model of fabric shielding efficiency based on flange coaxial test principle is effective.By comparing the simulation results of the shielding effectiveness of two fabric models,it is found that the simulation calculation efficiency of the shielding effectiveness based on the simplified fabric model is higher,and the consistency with the experimental test results is better.On the basis of verifying the effectiveness of the fabric shielding efficiency simulation model based on the flange coaxial test principle,the shielding performance of 10 kinds of fabrics with different conductive yarn content and arrangement mode was simulated.According to the shielding efficiency simulation results and electromagnetic field distribution,the influence of conductive yarn content and arrangement mode on the fabric shielding efficiency was discussed.The results show that when the content of conductive yarn increases,the increase amplitude of the fabric conductivity and the decrease amplitude of the wave impedance decrease gradually.Therefore,the shielding efficiency of the fabric increases with the increase of conductive yarn content,but the increase decreases gradually.However,when the content of conductive yarn exceeds 80.00%,the electrical conductivity and wave impedance of the fabric have little change,and the shielding efficiency of the fabric tends to be stable and is basically consistent with that of the fabric with the content of conductive yarn being 100%.In the fabric with 33.33% conductive yarn content,the larger the size of the mesh unit composed of different conductive yarn arrangements,the lower the effective resistance and wave impedance of the fabric,and the higher the shielding efficiency in the low frequency range(30-400 MHz),while the fabric with small mesh size shows a better shielding effect at the high frequency(400-1500MHz).However,with the increase of conductive yarn content,the shielding efficiency advantage of fabrics with large conductive mesh cell size decreases gradually in the low frequency range.The distribution of electromagnetic field shows that the content and arrangement of conductive yarn can change the direction of electric field,generate reverse magnetic field on conductive yarn parallel to the direction of electric field,affect the distribution of induced current in the fabric,and then affect the shielding efficiency of fabric.In order to further understand the shielding mechanism of multilayer fabric against electromagnetic wave,combined with the characteristics of multilayer fabric,a two-layer single-yarn directional periodic arrangement model was established as a simplified model of multilayer fabric.Then,the shielding efficiency of four kinds of fabrics with the content of conductive yarn of 11.11%,20.00%,33.33% and 50.00% was calculated by using the fabric shielding efficiency simulation model.The shielding efficiency test was carried out to verify the validity of the simulation results.On this basis,the influence of stacking Angle and stacking distance on shielding efficiency of multilayer fabric is analyzed.The results show that the shielding efficiency of multilayer fabric increases with the increase of the number of stacked layers,but the shielding efficiency increases gradually with the influence of the skin depth of the fabric.In addition,because the absorption loss is positively correlated with the thickness and frequency,the higher the conductive yarn content of the single-layer fabric,the more significant the shielding efficiency of the multilayer fabric in the high-frequency range.All the data points in the B-A diagram of the experimental and simulation results of the shielding efficiency of multi-layer fabric are within the 95% consistency interval,indicating that the simulation results of the shielding efficiency of multi-layer fabric with different conductive yarn content have a good consistency with the experimental results.In addition,the difference rate between the simulation and experimental results is less than 8%,which proves the validity of the simulation results.The shielding efficiency of the fabric can be improved by placing the fabric in a position or keeping a certain interval between layers.The shielding efficiency of the fabric is affected by the stacking Angle by changing the pore coverage and the propagation path of electromagnetic wave inside the fabric.The smaller the content of conductive yarn is,the greater the shielding efficiency is affected by the stacking Angle.Layer spacing can effectively improve the shielding efficiency by improving the multiple reflection of electromagnetic wave between layers.The greater the content of conductive yarn,the greater the influence of layer spacing on the shielding efficiency. |
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