Controlling seam aperture leakage

It is easy to accept that the maximum shielding effectiveness of an electronic enclosure can never exceed the attenuation provided by the skin material. Even then, differences in shielding effectiveness result from non-homogeneous effects caused by variations in material thickness, forming/bending/welding, and non-linear material behavior at different radio frequencies, field intensities, and source locations. This means that the same material will behave differently, depending on the circumstances in which it is being used. These variations are minor however when compared to the performance degradations caused by apertures in the enclosures needed to accommodate cables, switches, displays, and maintenance panels. The shielding effectiveness of these apertures, and ultimately of the enclosure itself, is a function of their number, area, and longest dimension. Since the worst-case parameter is the aperture's longest dimension, this makes enclosure seams around doors and access panels the greatest offenders.