Low Frequency Magnetic Shielding Effectiveness of a Conducting Plate With Periodic Apertures

This article focuses on the shielding effectiveness (SE) prediction of the periodic aperture array on an infinite PEC plate against the low frequency (≤1 MHz) magnetic field resulting from a current loop parallel to the plate. Two different models of the penetration field through the plate are presented. From the two models, the same simplified expression for the field on the central axis is derived. The SE of a 1000 mm × 1000 mm aluminum plate with 2500 apertures against the magnetic field from a current loop is measured. The results show that the theoretical results are in good agreement with the measurement if the frequency is higher than a critical frequency. Above the critical frequency, penetration from the apertures is primary factor for field leakage, and the SE is constant with the increasing frequency. When the frequency is lower than the critical frequency, penetration from the aluminum is primary channel for field leakage, and hence the SE reduces with the decreasing frequency. In this case, the upper limit of the SE does not exceed the SE of the corresponding solid plate without apertures.