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Q & A: magnetic shielding

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Most recent answer: 10/22/2007
Q:
Is there a material that can block magnetic flux at the same not be attracted by the magnets? I know that if you put an iron ring around a bar magnet, the magnetic flux outside the iron is greatly reduced. However, the iron ring is highly attractive to the magnets. Is there a material that can produce the effect of the iron ring yet be non-attractive to the magnets? Thank you in advance.
- Edward (age 29)
Maryland
A:
Yes, superconducting materials can also shield magnetic fields. The way they work is opposite to that of iron. Iron pulls the magnetic flux lines in and is thus attracted to regions of high field. Superconductors (at least Type 1 superconductors) expel magnetic flux and thus are repelled from regions of high magnetic fields. An iron wrapping around a magnet keeps most of the flux from getting out because it doesnít leave the iron. A superconducting wrapping keeps the flux from getting out because it doesnít even get into the superconductor.

There are, however, no known materials which superconduct at room temperature, so superconducting shielding can only be used where itís possible to cool things, say to liquid nitrogen temperature. Many superconducting materials require even lower temperatures, requiring the use of liquid helium.

Mike W.

(published on 10/22/2007)

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