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Old 6th January 2012, 08:08 PM   #11
tvrgeek is offline tvrgeek  United States
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The paper I read on mu-metal suggested any strain on it would disrupt the carbon crystalline structure making it no better than plain steel. Just a paper, no direct experience. Besides, I can't find anyone who sells it in less than ton lots, so maybe that is a hint.
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Old 6th January 2012, 08:26 PM   #12
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Try a search on mumetal and mushield. I've bought small quantities in the past with no problem. It's not cheap. If you find a junk oscilloscope, the CRT shields are usually some form of mumetal. I know I posted the aluminum trick quite a few years ago, but everybody knows aluminum and copper can't shield magnetic fields! Fun- drop a strong neo magnet down a piece of copper water pipe.
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Old 6th January 2012, 09:40 PM   #13
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Here it is:
Magnetic shields for transformers
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Old 7th January 2012, 02:02 PM   #14
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Mu metal is not particularly suitable for shielding power transformers as apart from the difficulty of working it without subsequent heat treatment it tends to saturate and then is ineffective. It is very good for shielding low level fields which is why it is used for signal transformers and tape head enclosures. Stalloy or similar alloys are deigned for the higher flux levels found around power transformers and are also easier to work.
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Old 7th January 2012, 02:58 PM   #15
DF96 is offline DF96  England
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Quote:
everybody knows aluminum and copper can't shield magnetic fields!
They can't shield static magnetic fields. They can shield varying ones if they are thick enough, or arranged in a loop, via eddy currents.
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Old 7th January 2012, 08:07 PM   #16
tvrgeek is offline tvrgeek  United States
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Stalloy. Not heard that term. Will WIKI. Thanks.
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Old 7th January 2012, 11:40 PM   #17
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The thickness of standard 1-ounce/foot_square copper foil,
at 35 microns or 1.4 mils, provides 1/E 1/2.178 attenuation
at about 5MHz, with progressively better attenuation for
higher frequencies per theory. Each 1/E is a neper, or 8.9dB,
thus 500MHz, 100x faster, would have 10 skin depths in that
same 1.4mil copper. Using a copper PLANE, to allow circulating
currents, provides 10 * 8.9 or 89dB for the high-speed-edge
energy of microprocessor clocks.
A 5MHz MPU clock would only be down 8.9dB, but assuming
1nanosec edges, the transient energy experiences wonderful
attenuation. This should permit integrating sensitive analog
circuits near modern MPUs, IF A PLANE (Vdd or GND or just SHIELD)
is between analog and MPU.
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Old 8th January 2012, 10:47 AM   #18
marce is offline marce  United Kingdom
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?
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Old 8th January 2012, 12:18 PM   #19
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McMaster-Carr

Nickel Iron Magnetic sheilding foil.
Doc
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