Re: [femm] Re: calulation of the magnetic flux

[David Meeker <dmeeker@xxxxxxxx>]

Michael Salloker wrote:

> Thank you for your reply David.
>
> One additional question: Assume I have two coils, coil 1 is the
> exciation coil with the current i1 and coil 2 has no current. How do
> I calculate the flux linking coil 2?
>
> Michael
>
> What can I do, if I want to calculate the flux through a coil excited
> by 
>
> > Perform the A.J volume integral and divide the result by the coil
> > current. This gives you the total flux linking your coil.
If you have no current in the coil, integrate A over the volume of the 
coil and multiply by:
(number of turns)/(coil cross section area). This will also work with 
coils that are carrying current. The only sort of "tricky" part is if 
you have more than one region contributing to the result, like in a 2D 
case. In that case, you add the contributions from the regions in which 
a positive coil current is directed out of the screen, and subtract the 
contributions from the region in which a positive coil current is 
directed into the screen. The advantage of doing the A.J integral 
instead (when you can, because the coil is carrying current) is that it 
sorts all of that part out automatically.

When in doubt, you could alternatively do an analysis with a trivial 
coil current in the coil with "no" current (e.g. 1e-6 A/mm^2) and do the 
Integral(A.J)/(coil current) approach where the coil current is that 
coil current that would be implied by the even 1e-6 A/mm^2 coil current 
density.

Anyhow, also see section 4.9 of the manual, which hits on these points, too.

Dave.
--
David Meeker
email: dmeeker@xxxxxxxx
www: http://femm.berlios.de/dmeeker