孔阵结构近场屏蔽特性有限元数值仿真

Numerical Simulation of Near-Field Shielding Properties for Aperture Arrays Based on FEM

为控制电子设备工作温度,设备机箱上一般设计有用于通风散热的孔阵.孔阵的存在造成了电磁能量的泄漏,导致设备内外电磁信号的相互干扰.当辐射源与屏蔽体间距及相邻屏蔽设备间距满足近场条件时,必需进行近场屏效分析.本文基于电磁场理论,阐述了孔阵屏蔽效能的有限元计算原理,对比分析了近场数值计算屏效和基于平面波理论计算屏效两种方法,研究了相关参数对近场屏效的影响规律,提出了提高近场屏效的设计方法,并在此基础上对不同形状孔阵进行了屏效数值计算.理论分析和仿真计算结果表明,基于平面波理论的孔阵屏效计算方法不能用于近场屏效计算,数值法是近场屏效计算的有效方法;数值仿真表明,在保证孔阵面积不变的条件下,通过减小孔规格与辐射源波长的比值、增加孔数可以提高近场屏效,但工程中常用的三种形状的孔阵近场屏效基本相同.

Aperture arrays are often designed to provide airflow through shielding walls so that the interior temperature of electronics equipment can be controlled bellow a required level. The electromagnetic energy leakage through the aperture arrays is inevitable, thus the near-field shielding effectiveness must be analyzed when the distance between the radiator and the shielding wall or the distance between two adjacent shielding walls satisfies the near-field condition. In this paper, the FEM for apertures is firstly introduced based on electromagnetic field theory, and the calculation approach of shielding effectiveness by numerical method and the formulation based on the plane wave theory are compared. Then, the effects of some related parameters on near-field shielding effectiveness are analyzed thoroughly. As a result, an approach to improve near-fteld shielding effectiveness is presented. By the FEM,tbe shielding effectiveness of aperture arrays with different shapes is analyzed. As the theoretical analysis and simulation results showing,the shielding effectiveness of aperture arrays is greatly overestimated by the classical plane wave theory and the numerical method is more effective in the calculation of near field. The results from numerical simulation shows that the near-field shielding effectiveness can be elevated by reducing the ratio of the size of an aperture to the wave-length of radiator or increasing the number of apertures while the area of apertures keeps unchanged, and three kinds of aperture arrays commonly used in engineering have the similar near-field shielding effectiveness.