Investigation For Electromagnetic Leakage From An Apertured Rectangular Cavity

Electromagnetic shielding is the primary technology for suppressing electromagnetic interference via field coupling channel. It can be implemented by using a metallic enclosure to enclose an interference source to lower its field leakage, or to screen a sensitive object by reducing external field strength. Although a closed metallic enclosure generally has very high shielding effectiveness (SE) for electromagnetic waves, apertures that exist inevitably on the enclosure for some practical functions can result in dramatic reduction of SE. Thus, lots of work has given attention to the effect of apertures on shielding effectiveness. Usually, in standard method for SE measurement, the SE of a shielding enclosure is defined as the ratio of the field strength at a given point with the enclosure removed to that at the same point with the enclosure applied. Where, the field source is required to be placed outside the enclosure. In other words, the field observation point is inside the enclosure, which has the advantage of reducing the potential influence of other unwanted interference source on the received field strength. As a result, in lots of literatures the SE of an enclosure is evaluated against an external field source.The electromagnetic field distributions in a rectangular metallic cavity excited by an electric dipole below resonance are calculated by using the analytical formulae obtained from the mode expansion method. Both the electric field and magnetic field distributions on the inner wall and within the cavity are presented. Then, an analytical formulation has been developed for the electromagnetic leakage from an apertured rectangular cavity excited internally by an electric dipole. The leakage fields are represented by equivalent electric and magnetic dipoles located at the aperture center with their dipole moments related to the "closed cavity" field according to the Bethe’s small aperture coupling theory. The "closed cavity" field is obtained by using the mode-expansion method. In this formulation, the leakage field can be expressed as a function of the frequency, the source point, the field point and the position of the aperture. Comparison with the full wave simulation software CST had verified the validation of the formulation over a very broad frequency bandwidth. Finally, an analytical formulation has been developed for the electromagnetic leakage from a plugging apertured rectangular cavity excited internally by an electric dipole. The model is also based on the mode expansion method to calculate magnetic field distribution on the inner wall, and then calculate the tangential component of the transmitted field, and finally reach the leakage field distribution though the surface magnetic current and vector potential.