Magnetic Shielding

It is often required to shield the electronic instruments, watches etc., from magnetic effects. The idea of preventing once components from affecting another through their common electric or magnetic field is called shielding. Examples are the braided copper-wire shield around the inner conductor of a coaxial cable, a metal shield can that encloses an RF coil, or a shield of magnetic material enclosing a cathode-ray tube.

The problem is shielding is to prevent one component from inducing an effect in the shielded components. The shielding materials are always metals. The best shield for a steady magnetic field is a good magnetic material of high permeability. A magnetic shield of high permeability concentrates the magnetic flux. Then there is little flux to induce poles in a component inside the shield. The shield can be considered as a short circuit for the lines of magnetic flux. The materials used for magnetic shield must have high saturation induction and very low coercively. The mumetal (Ni 48%, Fe 48.5%, C 3%, Mn 0.5%) and premalloy C are widely used for magnetic shielding.


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