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Electromagnetic shield

Latest Updated:02/01/2008

Question:

Electromagnetic shield

Answer:

This is a technique to shield against electromagnetic waves by using a metal box, metal plate, or metal mesh and thus avoid EMI & EMS. When an electromagnetic wave goes through these shielding materials, an eddy current is generated, canceling out the electromagnetic waves.
Generally, the shielding effect is enhanced by grounding the shielding material to make its potential the ground potential.
Coaxial cables that are used to connect a TV set to an antenna are shielded because their core is covered with a conductive mesh in the cables.

The following points should be noted when shielding against electromagnetic waves.

  • Shielding the noise generation source is more important but more difficult than shielding the receiving side of the noise.
  • If there is a weak part that is not completely shielded, energy is concentrated on that part.
  • Metal boxes and metal plates are less effective for heat radiation than metal mesh.

Since electromagnetic shielding is not absolute but one of means of suppressing noise, it is desirable to take a drastic action to suppress noise or use it in combination with other methods.

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To distribute and not to concentrate noise energy, a method to mitigate the effect of the noise energy by reducing the overall shielding effect or a method to mitigate the effect by providing a time difference to several causes are used. Renesas Electronics supplies, as an analog core, an SSCG (Spread Spectrum Clock Generation) that is a clock generator with a time difference function. The 32-bit microcontrollers V850E/ME2 and V850E2/ME3 are equipped with this clock generator, so that the IC takes measures not to radiate EMI.
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