EMI shielding-common problems and containment strategies

This discussion focuses on the sources and containment strategies for EMI. The operation of all electrical and electronic devices involves the changing of voltage or current levels either intermittently or continuously, sometimes at very fast rates. This results in the development of electro-magnetic energy at discrete frequencies as well as over frequency bands. The circuit will radiate this energy into the surrounding area and also into the wiring emerging along the external power, signal and control lines. It is this electro-magnetic energy which must be contained to meet international standards such as FCC (U.S.) or EC Directive (Europe). A gasket is required when the gaps, slots and holes around the connector/metal plate interface are such that they allow excessive radiation of the internally generated electro-magnetic frequencies, and if such radiation causes the equipment to emit electro-magnetic interference or is susceptible to such interference outside of the permitted levels.