Analysis On Shielding Effectiveness Of Enclosure With Off-center Aperture

Electromagnetic shielding is widely used to reduce emissions or improve the immunity of electronic equipment. However, the shielding effect is deteriorated by aperture in the wall of enclosure. But sometimes aperture in the wall is unavoidable for heat dissipation, air flow and so on. Thus, the study of shielding effectiveness is very necessary and practical.In this paper, the shielding effectiveness of enclosure with off-center aperture is investigated by Transmission Line Method. The effects of aperture's parameters on the shielding effectiveness are studied, such as position, ratio of the length to the width and quantity. Then the effect of polarization of incident electromagnetic wave on the shielding effectiveness is also studied.The result obtained by the approach proposed is basically in agreement with that obtained by CST. The results show that: the closer the aperture to the centre of the enclosure wall is, the worse the shielding effectiveness is; with the incident wave's E-field vector parallel to the y-axes, the smaller the ratio of the length to the width is, the higher the shielding effectiveness is; the more apertures there are, the worse shielding effectiveness is; with the polarization angle increasing, the shielding effectiveness is also increasing. So when the electric polarization vector is vertical to the length of the aperture, the shielding effectiveness is the lowest; with the increase of the aperture's depth, the shielding effectiveness is also increasing, but the frequencies corresponded to resonant points keep constant.Then we study the shielding effectiveness of double-layer rectangular enclosure with off-center aperture by Transmission Line Method. The waveguide equivalent circuit model and analytical formulations are proposed. We approximately calculate the equivalent impedence of the inner aperture. The result obtained by the approach proposed is basically in agreement with that obtained by CST. Similarly, the effects of inner aperture's parameters on the shielding effectiveness are also studied, such as position, ratio of the length to the width.