Effective EMI shielding concepts

ANP043

Despite all extensively discussed and recommended design rules for the EMC-conform design of components, the interaction between different functional groups within an apparatus has often a sobering effect when tested in the EMC laboratory. Although installed in a metal casing, the emitted interference radiation is above the threshold.

What has happened?
Most of the times, the casing itself is not part of the electronics development but is developed by the construction department. They make sure that the openings in the casing, e.g. for cable inlets and outlets, ventilation slots, operating buttons, speakers, transducers or displays cause a massive reduction of the shielding action. But even if the desired openings in the casing were not existent, no complete overlap and hence no RF-density is attainable for contiguous metal surfaces.

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