Modern microelectronics depends on the control of
electromagnetic interference. The maximum allowable interference is now set by
regulation in most countries. In the USA, the FCC regulates
emission standards. In
Europe, the emissivity standards came into force in 1982 and
have been mandatory for makers of electronic/electrical equipment
(Mobile, and Notebook etc.) since January 1, 1996.
Some forms of interference can be controlled by
suppression of components and good circuit design. Enclosing the circuitry in a
shielded enclosure best controls radiated interference. Metal enclosures
generally offer very good shielding. Metals are highly conductive and will
absorb or reflect electromagnetic waves. A seamless metal sphere offers the
ultimate shielding.
Plastics provide the
enclosure designer with several advantages over metal. Reductions
in weight and cost coupled with increased flexibility and
aesthetic appeal have led to increased use of polymers. However,
plastics are non-conductive and are transparent to electromagnetic
waves. Uncoated plastics offer no protection against EMI.
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