Effective EMI shielding concepts

ANP043

Despite all extensively discussed and recommended design rules for the EMC conformity design of components, the interaction between different functional groups within an apparatus can often lead to un-wanted side effects when tested in the EMC laboratory. Although installed in a metal casing, it can happen that the emitted interference radiation is above the threshold.

What has happened?
Most of the times, the metal casing itself is not part of the electronics development but is developed by the construction/mechanical 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 and all of these can cause a massive reduction of the shielding action. But within the openings of the metal casing, it is not possible to have a complete seal of both halves and so without overlap the result is that RF emissions can pass through.

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