Research On Shielding Effectiveness Testing Method Of Small Space Cavity With Irregular Structure

With the development of science and technology,the electromagnetic environment is getting worse and worse,and it is more and more important to protect products from electromagnetic interference.Electromagnetic shielding is a commonly used protection method,and the research interest in this field is continuously growing.In addition,special shielding cavity may need to be designed for some special equipment,and the shielding performance of the designed shielding cavity needs to be verified by testing.However,in practical situations,when designing a shielding cavity,it is often impossible to have a quantitative estimate of its shielding performance in the design stage,and actual tests are required in the acceptance stage to verify the performance of the designed shielding cavity.For the purpose of ventilation and heat dissipation,wiring installation,etc.,there will be holes and slits on the surface of the cavity,and there is irregular structure inside the cavity.Due to the limited space of the cavity,conventional test standards may not be applicable.Therefore,it is necessary to quantitatively evaluate the shielding performance of the cavity in design stage,even establish a more systematic evaluation model,as well as have a good understanding of the field distribution characteristics of cavity.At the same time,it is also necessary to study the shielding effectiveness test method of this type of cavity.Aiming at the problem that the shielding effectiveness of the shielding cavity cannot be accurately estimated in the design stage,this paper adopts an analytical algorithm to analyze shielding effectiveness of the small space cavity with irregular structure,which can provide more effective calculation and analysis in the design stage.This paper starts from Robinson algorithm,extends it to the case of special-shaped cavity,and by introducing electromagnetic topology theory,transforms the physical model of radiation source irradiating special-shaped cavity into an equivalent transmission line BLT network and signal flow diagram,and decomposes the complex system into different levels of network structure.According to the properties of the transmission lines and nodes of the divided network,the supermatrices in the BLT equation are calculated,and the response of the entire system can be obtained by solving the BLT equation.Aiming at the problem that the irregular structure affects the field distribution of the shielding cavity,this paper uses CST simulation to analyze the influence of the irregular structure on the field distribution of the shielding cavity,and combines the principle to explain the reason why ‘the inductive structure’ in the irregular structure has a greater influence on the field distribution.Due to the simulation results,the possible maximum field strength position in the cavity is given,and suggestions for the selection of relevant test monitoring points for the shielding effectiveness of the small space cavity with irregular structure are proposed.According to the field distribution research,based on the current test standards for the characterization and test method of the shielding effectiveness of the cavity,the characterization technology and test method for the shielding effectiveness of the small space cavity with irregular structure are given,and the requirements for the development of the test system are proposed.Aiming at the problem that there is no suitable test system for the shielding effectiveness test of the small space cavity with irregular structure,this paper starts from the development requirements of the small-sized field strength probe,analyzes the scheme selection of various probes,and chooses the spherical dipole antenna research scheme.Firstly,the spherical structure and each component module of the antenna are designed,including internal circuit,impedance matching network,optoelectronic module and power module.Then the performance of spherical dipole antenna is tested and verified,including frequency response and antenna factor,sensitivity and dynamic range.Finally,the newly designed test system and the proposed test method are used to test and verify the shielding effectiveness of the small space cavity with irregular structure.