Study On The Measurement Of Shielding Effectiveness And The Mechanism Of A Shielding Material

The increasingly complex electromagnetic environment has an impact on human production and life.Electromagnetic shielding technology is an effective measure to cut off the coupling way,and the application of shielding technology is inseparable from the research and design of shielding materials.Moreover,the measurement of shielding effectiveness of shielding materials is the basis of research work,and provide measurement data source for analysis of material properties.Firstly,this paper studies the shielding effectiveness measurement methods,expounds the principles and steps of the shielding chamber window method and flange coaxial method,as well as the electromagnetic field type,measurement frequency band,material type and other attributes.In order to improve the measurement efficiency and accuracy,based on the shielding room method,built an automatic measurement system of shielding effectiveness.GPIB interface is used to connect the measuring equipment such as computer,receiver and signal generator.In combination with the corresponding frequency band antenna,power amplifier and attenuator,the automatic measurement software is written using Visual C++ language,realize the management of instrument library and antenna library,and control the instrument work.According to the standard requirements of measurement and data processing,achieved shielding efficiency automatic measurement function of 9k Hz-3GHz full frequency band.Secondly,the window method is used to measure the magnetic shielding effectiveness of the conductive cloth material.When the thickness of the material is increased to 8 layers,the shielding effectiveness increase to 25 d B at 14 k Hz,83 d B at15 MHz,which can meet the requirements of general engineering applications;Flange coaxial method is used to measure the variation trend of shielding efficiency of conductive sponge in 30MHz-1.5GHz frequency band,and designed a kind of combined structure of "conductive layer-dielectric layer-conductive layer".The combined material value of 30MHz-500 MHz frequency band can be increased by more than 10 d B,and the specific frequency band can be increased by 30 d B.Scattering parameters were extracted by network analyzer,and the electromagnetic parameters with frequency was obtained by theoretical calculation.Then,used electromagnetic simulation software HFSS to verify the improving effect of composite structure materials on shielding efficiency.In order to study the shielding performance characteristics of mixed materials,a set of flange coaxial fixture was designed and developed to realize the measurement of discrete structure shielding materials and expand the types of materials measured by the flange coaxial method.Finally,the paper analyzed the mechanism of frequency selective surface material and established the corresponding circuit equivalent model.Design single-layer bandstop FSS with center frequency of 1GHz,the FSS surface meet the transmission coefficient S21 <-20 d B,and the bandwidth of-5d B is about 110 MHz.Then processed the real object and used the flange coaxial method to measure the S21 performance of it.The results are basically consistent with the simulation.In order to expand the bandwidth,a double-layer square ring FSS is designed to realize the dual band stop function of 1GHz and 2GHz,the S21 of 1GHz is reduced to about-40 d B,and the bandwidth of-5d B is increased to more than 500 MHz,which effectively improved the bandwidth stability of materials.In order to achieve miniaturization of FSS,a folded square ring structure was designed.The size was reduced to 1/2 under the condition of constant resonant frequency.The design of 2.5-D structure reduces the size of FSS unit to 1/7 of the original,and realizes a wider stopband width.