Interactions Between Slots, Apertures, and External Features in Shielding Enclosures

A susceptibility was identified experimentally when an external feature was added near an irregular aperture that spanned two faces of the shielding enclosure of an equipment under test. The susceptibility was due to a resonant response that occurred at a lower frequency than that expected by the resonances of the aperture, enclosure cavity, or external feature considered in isolation. Numerical modeling showed that currents induced on the exterior of the enclosure when the external feature is in place couple to the currents surrounding the aperture, leading to a longer resonant length than provided by the aperture alone. The resonant response giving the susceptibility was observed with various changes in aperture and external feature dimensions, provided that the aperture spanned two faces and the external feature was aligned with the enclosure edge that the aperture spanned. The low-frequency susceptibility can be mitigated by electrically connecting the external feature to the enclosure edge to interrupt the external current path. The higher-frequency resonant coupling due to the irregular aperture alone was not affected by the suppression of the external current.