Study On Topological Model Of Shielding Efficiency Of Heterogeneous Cavity

The increasing frequency of communication signals in modern communication systems has led to a complex electromagnetic environment.This complex environment raises the electromagnetic protection requirements for sensitive electronic devices.Therefore,shielded enclosures are commonly used to meet the electromagnetic protection requirements of these devices.Shielding effectiveness is typically used to measure the shielding capability of shielded enclosures.The calculation of shielding effectiveness is mainly done using numerical methods and analytical methods.Numerical methods include Finite-Difference Time-Domain method,Method of Moments,and Finite Element Method.Although numerical methods can accurately calculate the shielding effectiveness of shielded enclosures with complex structures,the running of numerical methods is affected by computer configuration.Analytical methods have the advantages of efficiency and accuracy over numerical methods and are a popular method for calculating shielding effectiveness.The representative method in analytical methods is the BLT(Baum-Liu-Tesche)equation topology model.The BLT equation topology model is relatively mature in calculating the shielding effectiveness of a single-layer hollow rectangular cavity.Considering that the number and position of holes,the size of internal components,and the structure of the cavity will all affect the shielding effectiveness in engineering,and relevant research is scarce.Therefore,further improving the BLT equation topology model is of great practical significance.This article analyzes the electromagnetic coupling process of double-layer shielded enclosures,shielded enclosures with built-in dielectric plates,and heterogeneous enclosures,and then establishes corresponding BLT equation topology models,providing a solid theoretical basis for meeting the electromagnetic protection requirements of sensitive electronic devices.The main innovations of this article are as follows:First,considering the structural characteristics of the inner cavity in the double-layer shielded enclosure,the scattering matrix of the inner cavity opening cavity wall is established using Electromagnetic Topology theory.By combining the scattering matrix with the Robinson algorithm,a BLT equation topology model that can calculate the shielding effectiveness of the double-layer shielded enclosure is obtained.Considering that holes and the double-layer shielded enclosure have different electric field distributions at high frequencies,the hole mode index is introduced to correct the traditional eccentricity coefficient.The modified eccentricity coefficient and the Robinson hole array impedance model are used to extend the BLT equation topology model,and the relationship between holes and the shielding effectiveness of the double-layer shielded enclosure is studied,including the relationship between the outer cavity hole position and the shielding effectiveness of the enclosure,the relationship between the inner cavity hole position and the shielding effectiveness of the enclosure,and the relationship between the number of holes and the shielding effectiveness of the enclosure.By comparing the results of the BLT equation topology model with the electromagnetic simulation software CST(CST Studio Suite)simulation results,the validity and efficiency of the BLT equation topology model are verified.Reliable design suggestions are obtained for the problem of ineffective shielding capacity caused by unreasonable hole positions and quantities in double-layer shielded enclosures.Second,to accurately study the electromagnetic shielding capability of a shielded chassis,it can be equivalent to a built-in dielectric plate with an opening cavity.Considering the limitations of the dielectric plate equivalent admittance model in the existing equivalent model of the shielding effectiveness of the cavity with an opening in the dielectric plate,the effect of the height,thickness,and position of the dielectric plate on the equivalent admittance model of the dielectric plate is taken into account.An accurate BLT equation topology model of the built-in dielectric plate cavity is established,which can calculate the shielding effectiveness of the cavity with any height,thickness,and position of the built-in dielectric plate.The BLT equation topology model,TLM(Transmission Line Method)calculation results,and CST simulation results are compared,and the shielding effectiveness average error is introduced as an evaluation criterion to verify that the BLT equation topology model has the characteristics of high efficiency and accuracy.The effects of the height,thickness,and position of the dielectric plate on the shielding effectiveness of the cavity in three different resonant modes are explored,and the results can provide reference for the electromagnetic shielding design of the built-in circuit board shielded chassis.Finally,the cavity structure will affect the propagation path of interfering electromagnetic waves inside the cavity,thereby changing the shielding effectiveness of the cavity.Based on the shape and extension direction of the cavity wall opening,heterogeneous cavities are classified into single cavities and composite cavities.The single cavities include curved surface cavities and polygonal cavities.A universal model of propagation impedance and propagation coefficient of single cavities is established,and a BLT equation topology model that can calculate the shielding effectiveness of any size single cavity is derived.The composite cavities include three types of cavities with opening cavity wall extensions perpendicular,curved,and oblique to the cavity wall.Based on differential equations,the corresponding BLT equation topology models of the above three composite cavities are established.Using the CST simulation results as the baseline,the Pearson correlation coefficient is introduced to discuss the correlation between the BLT equation topology model,TLM calculation results,and baseline value.The effectiveness of the BLT equation topology model and TLM calculation resonant frequency are discussed using resonant frequency error.The resources and computation time required for the above three shielding effectiveness calculation methods are compared.The validity and rapidity of the topological model of BLT equation are confirmed,which provides a solid theoretical basis for the calculation of shielding efficiency of single cavity and composite cavity.