Re: [femm] Scaling question

[David Meeker <dmeeker@xxxxxxxxxxxxxxxxx>]

David Meeker wrote:

> All of this falls out of considering Ampere's loop law:
>
> Path Length*Field Intensity = Amp-Turns

Ack. What I meant to say was that in the case of an unsaturated c-core magnet,
you can neglect the iron sections of the flux path and approximate Ampere's loop
law (which says that the line integral of H around the edge of some surface S
equals the total amp-turns that pass normal to S) can be simplified a bit. In
this case, the flux density in the middle of the gap can be assumed to be
constant across the gap, and the flux density for both air gaps is the same. H
is approximately zero in the iron. The path length is then 2*(air gap length),
and the Field intensity is the gap flux density divided by the permeability of
free space. You then get:

2*g*Bgap/(mu_o) = n*i

where g is the gap length, Bgap the air gap flux density, mu_o the permeability
of free space, and n*i the total number of amp-turns....

Dave.


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