An eccentric inventor friend of mine has given me a roll of hi-quality Siemens VacuPerm 70 final annealed hi-permiability Mumetal foil to sell for him. It is 0.1 mm (0.004") thick x 155mm (6") wide with an adhesive backing. I have some information & links below including current price quotes.
Sold Out...
If you have any questions please email me -- Dave
Buyer pays actual shipping. Money Orders, Visa, Mastercard, or Cash (if you want
to chance it). 7% GST will be added for Canadian residents; 7.5% PST will be added
for BC residents.
What is Mumetal?
Mu metal is a "soft" ferromagnetic material, as opposed to "hard"
ferromagnetics that retain a macroscopic internal field after removal of an external
magnetizing field. Most alloys are about 80% Ni, near 20% Fe, some Mo and I presume
Co in specific alloys. Low C or "mild" steel is also a soft ferromagnetic
material, and thus is suitable for magnetic shielding. Construction grade mu metal,
like that used here in our MEG machine room, has a magnetic shielding effectiveness
100x to 1000x higher than mild steel for equivalent thickness.
Ferromagnetism originates at the quantum level. Ferromagnetic elements have a lowest
energy e- orbital state that aligns the e- spins
parallel, thus giving an intrinsic magnetic moment to the atom. The lowest microscopic
energy state of an ensemble of atoms is, somewhat counterintuitively, with these
magnetic moments aligned to produce a net magnetic field. Since maintaining an external
magnetic field would require energy, the lowest macroscopic energy state requires
that the atoms divide into domains about 1000 atoms across and that the magnetic
orientation of these domains be randomized.
In the presence of an externally applied magnetic field, the domains magnetically
realign to some degree and thus generate their own external field. The primary field
continues to exist, but now the net field is the sum (or superposition) of the primary
and induced field. The induced field must have an alignment of _opposite_polarity_
to the primary field (just like two bar magnets must align N to S and S to N), and
the superposition of the two fields results in a lower observed field - voila, magnetic
shielding.
The position and alignment of the shield matters. Shields aligned parallel to the
"lines of force" from the source will be much more
effective than when aligned perpendicular. You can even shield by placing the shielding
beyond the shielded object, although since the source field falls off with distance,
the induced field in the shield will be smaller and less effective.
Regarding annealing, the manufacturers claim an increase in magnetic permeability
mu of about 40x by hydrogen annealing. The annealing serves two purposes; grain alignment
to lower the reluctance, raising the mu, and the removal of impurities such as C.
Working the material can disturb the grain boundaries and increase reluctance, but
I'd guess that this effect only matters in the most critical applications, which
must be annealed after fabrication. I'd also guess that even the most roughly handled,
whacked out mu metal would still be an orders of magnitude more effective shield
than mild steel.
Above extracted from a JoeList post by Tim
Reese
Price Quotes
received near the middle of May, price per foot2 in USD
|
Vendor |
Unbacked* |
Adhesive Back* |
Comments |
|
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| Haug & Co |
13.80 - 23.20 |
18.22 - 30.88 |
dependent on quantity | |
| MuShield |
|
|
coming | |
| LessEMF Inc. |
7.11-14.21 |
|
as little as a foot | |
| Magnetic Shield Corp |
|
26.72 |
dependent on quantity | |
| Advance Magnetics |
|
22.97 |
1-9 ft quantity | |
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