Re: [femm] Magnetization circumferencely

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

wilsons@xxxxxxxxxx wrote:

> Hi I am a new user of femm and am trying to get a circular donut
> magnatized cicumferencely and am having a hard time figuring out how
> to do this. I am a senior level college physics student and have
> tried everything that I could figure out. Any help in this would be
> greatly appreciated. Thanks in advance.
> Jason

There are a couple of ways that you could do this. A physical configuration
that actually acts this way is a toroidal core wrapped with wire. A 2-D
planar simulation would be modeling an axial cross-section of the toroid.
To make the field, you then have to model the coils that would be wound on
the toroid. This would consist of a circular region in the bore of the
toroid defined with a current density. You could then put a second coil
region external to the toroid, also with a current density defined--this
current density should be the negative of the value defined in the bore.
Then, specify A=0 on the outer boundary of the outer coil. This results in
a purely circumferential field in the iron. See cylinder2b.fem in the
attached zip.

A different "quick and dirty" way to make a circumferential field is to
assign the inner bore of the toroid to be A=0 and assign the outer boundary
of the toroid to be some nonzero value of A. Specifically, if you want an
average flux density to be B in the toroid (that is, the average of B along
any radial line linking the inner and outer boundaries of the toroid),
define the outer boundary to be A=B(ro-ri), where ro is the outer radius of
the toroid, and ri is the inner radius. See cylinder2a.fem in the attached
zip.

Dave.


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