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Old 9th March 2011, 02:44 PM   #1
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Default Mu-Metal and Magnets ?

Do magnets stick to mu-metal ?

Magnets stick to steel, but do not stick to stainless steel (confirmed that first-hand this morning). Just wonder about mu-metal.

Anyone know ?


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Old 9th March 2011, 05:36 PM   #2
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magnets saturate mu metal at much lower B value than iron so the "holding/lifting" force may feel unexpectedly low - since mu metal is often supplied in thin sheets too the force would be small

and until you degauss your mu metal its useless for low level mag shielding after playing with a magnet
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Old 9th March 2011, 06:18 PM   #3
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I have some mumetal downstairs somewhere. making an experiment a possibility.

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Old 9th March 2011, 06:54 PM   #4
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magnet's "holding/lifting" force can be looked at from an energy perspective

a magnet "engergies" a region of space with B*H/vol

a high perm material lets the field complete thru a shorter distance, leaving less energy in the system

so a thick piece of iron can mostly "short out" nearly 1/2 the external field of a magnet - the holding force can be calculated as the change in mag field energy for a small relative movment

a thin iron sheet saturates, can't conduct all of the magnetic flux, so there is still external mag field in the air on the far side of a thin, saturated sheet and the force is much smaller since a small separation of magnet and saturated thin sheet doesn't change the external mag field much

mu metal saturates at a fraction the level that iron/low carbon steel so the force from moving a magnet close to a thin sheet of mu metal is even lower
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Old 9th March 2011, 07:09 PM   #5
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Thanks guys for helping me puzzle this out (will probably order some, but am curious about what to expect with this stuff). Google found someone else that indicated that it's less magnetic than steel (but maybe because it's normally so thin).

Let me rephrase the question, if it helps, to understand how magnetic we are talking about . . .

Does mu-metal stick to a magnet ?


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Old 9th March 2011, 07:40 PM   #6
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Quote:
Originally Posted by johnferrier View Post
Thanks guys for helping me puzzle this out (will probably order some, but am curious about what to expect with this stuff). Google found someone else that indicated that it's less magnetic than steel (but maybe because it's normally so thin).

Let me rephrase the question, if it helps, to understand how magnetic we are talking about . . .

Does mu-metal stick to a magnet ?


.
Yes.
There is no known material that blocks magnetic fields without itself being attracted to the magnetic force. Magnetic fields can only be redirected, not created or removed. To do this, high-permeability shielding alloys are used. The magnetic field lines are strongly attracted into the shielding material. There are many types of shielding materials.
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Old 9th March 2011, 08:08 PM   #7
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Quote:
Originally Posted by AEIOU View Post
Yes.
There is no known material that blocks magnetic fields without itself being attracted to the magnetic force. Magnetic fields can only be redirected, not created or removed. To do this, high-permeability shielding alloys are used. The magnetic field lines are strongly attracted into the shielding material. There are many types of shielding materials.
Okay. So, a stainless steel enclosure is not going shield magnetic fields (from chokes/torroid). Currently, I'm using distance to prevent hum, but I'd like to add mu-metal (having a wrap around, in mind, rather than simply a flat sheet as a barrier).


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Old 9th March 2011, 08:38 PM   #8
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Quote:
Originally Posted by johnferrier View Post
Okay. So, a stainless steel enclosure is not going shield magnetic fields (from chokes/torroid). Currently, I'm using distance to prevent hum, but I'd like to add mu-metal (having a wrap around, in mind, rather than simply a flat sheet as a barrier).
You might be interested in this material.
SALE! - Rare Ultraperm 80 Shielding Sheet-The Electronic Goldmine
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Old 9th March 2011, 08:56 PM   #9
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Iron/low carbon steel is much cheaper so you can use lots, box source and "victim" circuits separately with air space

don't use mu metal near the xfmr: it will saturate, only useful after other measures have cut the mag field down - usually used to just box the most sensitive part of "victim" circuits
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Old 9th March 2011, 09:15 PM   #10
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Mu-metal - Wikipedia, the free encyclopedia

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