Question in permanent magnet calcalutions 2

[janas21]

Hello, I have an Alnico magnet with its demagnetization curve, Br & Hc. It is a brick with well known dimensions.

I want to do some calculations-simulations.

How can i take from this magnet a 100mT magnetic field?

Thanks in advance.

 

[electricpete]

MagMike gave me this link which may help answer your questions. One piece of data I think you'll need is Residual induction (Br). All calculations are in units of G and of course 1G=1e-4 T

http://www.dextermag.com/CalculationList.aspx

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[MagMike]

If your requirement is simply for a 100mT field, and you are not concerned with uniformity or producing a large region of 100mT field:
1) Decide where (relative to the magnet) you need the 100mT field
2) Use one of the web-based calculators (such as

http://www.dextermag.com/CalculationList.aspx

)and input the appropriate values. For Alnico, it'll only be an estimated value since the field calculator doesn't directly factor in the Hc value.

If you need a uniform 100mT field, or anything more complicated, either contact the vendor that supplied the magnet (for engineering support) or use FEA.

 

[electricpete]

A Helmholtz coil is one configuration apparently designed to give a uniform field over a limited region.

It is discussed here:

http://en.wikipedia.org/wiki/Helmholtz_coil

I see they show the uniformity of the field with distance along the axes at the exact center of the coil. Does anyone know how it changes as we go outside that center?

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[MagMike]

Hello electricpete,

The rule of thumb is the central 1/3 of the volume is uniform.

As an FYI: While Helmholz coils are terrific for producing uniform magnetic fields, they generally do not produce very large magnetic fields.