Study on electromagnetic shield of a lossy shielding screen with apertures

用解析和实验相结合的方法研究了开孔电磁屏蔽板的屏蔽效应。在解析研究中，我们得到了一个格林函数，它代表了有耗地平面上一个源的辐射场。还得到了光波导场的格林函数。引入了表面阻抗边界条件，简化了屏蔽板有耗表面的边界条件。利用这些格林函数，得到了有耗屏幕缝隙散射场的解析结果。研究发现，当频率高于共振频率时，薄磁性涂层降低了通过缝隙的传输功率，而当频率低于共振频率时，涂层增加了传输功率。当我们使用磁性涂层材料来减少通过缝隙的电磁波泄漏时，这种通过缝隙的传输功率的频率依赖关系是很重要的。在实验研究中，测量了覆盖有吸收材料的金属板中缝隙的散射场。作为对实际电磁场屏蔽的研究，对一栋公寓楼的工频磁场进行了测量。提出了一种有效降低工频磁场的方法。

Shielding effect of electromagnetic shielding plates with apertures, a simple model of a shielding case of an electric device, was studied both analytically and experimentally. In the analytical study, we obtained a Green's function which represents the fields radiated from a source on a lossy ground plane. A Green's function for the field in a waveguide was also obtained. A surface impedance boundary condition was introduced to simplify the boundary conditions for the lossy surfaces of the shielding plates. By using these Green's functions, analytical results of the field scattered by a slot in a lossy screen were obtained. It was found that a thin magnetic coating reduces the transmission power through a slot for the frequency higher than the resonant frequency, while for the frequency lower than the resonance the coating increases the transmission power. This frequency dependence of the transmission power through a slot is important when we use a magnetic coating material to reduce electromagnetic wave leakage through a slot.In the experimental study, the scattered fields by a slot in a metal plate covered with an absorbing material were measured. The results are generally consistent with analytically predicted one.As a study of shielding of an actual electromagnetic field, measurements of power frequency magnetic fields in an apartment building were performed. An effective technique to reduce power frequency magnetic fields were proposed.