Magnetic Shielding

Most recent answer: 10/22/2007

Q:
I have been unable to find this question answered and you guys have the most user friendly website I have found. My questions is: What materials would prevent two magnets from attracting to each other when placed between them?
- James
Melbourne, Victoria, Australia
A:
Magnetic fields don’t penetrate type I superconductors, so a big sheet of one of them would work. Of course it would have to be kept cold, and if the fields are too big it just quits superconducting.

Highly magnetizable material (mu-metal) can also work, if it’s arranged in the right geometry. Mu-metal does the opposite of the superconductor. It pulls magnetic field lines in, rather than expelling them. A loop of mu-metal from one pole to the other of one of the magnets would keep that magnet’s field from extending out as much as it normally would. Of course, a strip of mumetal from one magnet toward the other magnet can actually increase the attraction.

Mike W.

(published on 10/22/2007)

Follow-Up #1: mu-metal shielding

Q:
Can changing magnetic fields also be shielded by high permeability ferromagnetic materials? Let's imagine having a magnet that is moving all around a ferromagnetic surface, is the magnetic field being shielded? (Ignoring Eddy Currents since most ferromagnets are conductors).
- Moe (age 20)
A:

That's the mu-metal shielding to which we referred. So long as it's arranged in the right pattern, it can shield fields. It was used to cover phonograph cartridges to reduce magnetic pick-up. It's used for low-noise signal transformers for the same reason. We just encased a low-noise experiment in a large mu-metal chamber for shielding.

Mike W.


(published on 08/26/2013)

Follow-up on this answer