Can magnetism be shielded

Answer 1

Mu-metal does a pretty good job for smaller fields, but completely shielding something from a magnetic field with a high field strength is not doable. Giron is supposed to be pretty good, and so is MetGlas, but they cannot stop (deflect) all the field lines from a strong field. Highly permeable material is the best shielding. Magnetic lines of force like to travel through permeable materials. That's what permeable means - an easy (easier) route than through space, air, whatever, for magnetic lines of force. What these shielding materials are doing is giving the magnetic lines of force a place to travel other than through space or through whatever is being shielded. The field still exists, but it's concentrated inside the shielding. And the lines of force will reappear from inside the shielding material at its edges. What else would one expect? The shielding can't make the lines of force disappear. As it re-routes them, it means that it has to re-release them somehow. Field density at the edges of shielding will be high. The field is collected for re-routing and distributed back into space after re-routing at a shield's edges. The materials cited are passive shields. Active shields can be constructed, but they are most challenging to engineer. Active magnetic shielding is used in the machinery for magnetic resonance imaging (MRI), and it is an active winding that is driven by an electronics package so that it "cancels out" fields outside the main coil. It's a headache and a half to design and implement active shielding. No shielding can block, stop, or re-route all the magnetic field lines from a magnetic source. Some lines of force will not be re-routed through the shielding and will appear on the other side of it.

Answer 2

A shield against a varying magnetic field needs only to be a good conductor. Screening cans are almost always made of aluminium. Shielding against a static field requires a magnetic material. In practice, shielding against low frequency fields is difficult with non-magnetic materials, and mu-metal is a commonly used material.

Answer 3

The exact details are a little complicated, but essentially the answer is yes: any object completely surrounded by conductive material will be shielded to some extent from an external magnetic field.