In this paper, a method of moments formulation is proposed to characterise the shielding effectiveness and the position of resonance frequencies in partitioned metallic rectangular enclosures. The formulation is based on a boundary integral equation technique only involving the discretisation of the unknown magnetic surface currents flowing in the apertures. An optimised Ewald transformation for the Green's function series expansion of the enclosure is used, especially near the edges of the enclosure. Numerical results for the shielding effectiveness of large metal backplane(s) in the enclosure are presented showing that the orientation has a great influence on the internal field distributions and the resonance frequencies. Finally, the shielding effectiveness of a loaded enclosure with PCBs and with an aperture in its wall is also investigated. All the examples show that our numerical technique yields an accurate prediction of the shielding effect of the PCB(s) over a broad frequency range. Moreover the resonances for the loaded enclosures can be predicted accurately.
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