Study On Near-Feld Shielding Effectiveness Of An Enclosure With An Aperture

With the trend of high frequency and high integration of electronic technology,almost all the devices are in the potential influence of the surrounding electromagnetic field,and the electromagnetic compatibility(EMC)is becoming more and more important.The metal enclosure behaviors well in electromagnetic shielding,which makes it an important means of EMC.Due to the need of ventilation,heat dissipation and external observation,some apertures are inevitable,and the aperture is the key factor that affects the shielding effectiveness.The device has to coexist in a compact space,and the sensitive device is often in the near field region of the interference source.In the near field region,the intensity of electromagnetic field and wave impedance are inhomogeneous.Therefore,it is important to study the near field shielding effectiveness of the enclosure with an aperture.Based on the finite difference time domain(FDTD)method,the factors affecting the shielding effectiveness of the aperture enclosure are analyzed.Based on the orthogonal test method,the influence degree and the primary and secondary order of the shielding effectiveness of the various factors are analyzed.The contribution of the thesis is listed as follows:Firstly,the basic principle of FDTD method and finite difference scheme are introduced,and the stability condition of Courant is given.The boundary conditions of free space and ideal conductor are derived.The Gedney perfectly matched layer(PML)is studied,and the absorption effect is verified by programming.The introduction of excitation source is analyzed and studied in this thesis.Secondly,the shielding effectiveness analysis model is established,and the numerical solution of the shielding effectiveness is obtained,which is in agreement with the conclusion of the equivalent transmission line(ETL)method.By introducing the electric dipole,the different factors,such as the size of the aperture,the shape of the aperture,the distance from the source to aperture,and the offset distance of the source and the observation point,which influence the near field shielding effectiveness is studied.Finally,a set of orthogonal experiments are designed.Through the analysis of Visual analysis and variance analysis,the primary and secondary order.The optimal combination of factors is determined and the shielding effectiveness is optimized.The work and results of this thesis provide a theoretical basis for the designing of EMC in the near field of the apertured enclosure,which be used to guide the engineering practice.