How can I protect a device from magnetic field?

Answer 1

surrounding it with copper

Answer 2

I assume that you are referring to low frequency (or static) magnetic fields. Note that this answer may not apply to high frequency fields. The answer is more complex if the fields are changing. If you are interested in quickly changing fields, you should post a new question specifically about that.

There is no way to completely "shield" anything from a magnetic field because magnetic field lines must always find some path back to their source. (in other words, complete shielding is not possible due to the lack of "magnetic monopoles")

However, field lines can be gathered up within objects with a high "magnetic permeability." For example, an object made of iron will have a higher magnetic permeability than air, thus magnetic lines will tend to flow through iron objects more easily than they will through air.

Thus, if you can provide a highly permeable path for flux lines to return to their source, then that path will be followed more readily than paths through the air. (see the first source below for an example) Note that some lines may still pass through the shield, especially with large fields. However, less will penetrate the area "behind" the shield than would without it.

So you need to look for permeable materials. See the second source below for some examples. Note that *NOT* all metals are good shields.

You may want to check out the third source below, on "Mu-metal," which is a special alloy with a very high magnetic permeability. To quote it, "The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields, which cannot be attenuated by other methods."

Answer 3

Sheild it with a metalic covering that is grounded. The metal should be a good conductor.

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Answer 4

Keep it in a safer place !! duhh !!