Study on electromagnetic shield of a lossy shielding screen with apertures

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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.