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# Re: [femm] Inductance - more confusion

- To: femm@yahoogroups.com
- Subject: Re: [femm] Inductance - more confusion
- From: dcm3c@aol.com
- Date: Sun, 9 Sep 2001 23:18:51 EDT

In a message dated 9/7/01 8:04:22 AM Eastern Daylight Time,
jim.bloor@smiths-aerospace.com writes:

> Hi
> Thanks to everone who responded to my plea for info on calculating
> inductance. However, I've now received some conflicting
> information. I understand that to determine inductance requires
> selecting an area of the model and obtaining the energy by
> integrating but one source says "integrate over the whole model"
> which I take to mean everything right out to the boundary, whilst the
> other source says "integrate only over the copper winding area".
> Which is correct?
> My feeling is that integrating over the whole model is the right way
> because the energy originates only from the coil. The magnetic flux
> generated would interact with the whole of the model and thus affect
> the inductance.

Just to elaborate a bit on Jim's response, you can limit the integration
region to the coils when you're using the A.J approach. As Jim has noted, it
doesn't hurt to use the entire domain for a single-coil, magnetostatic
problem, because A.J is equal to zero outside the coil anyhow. However,
there are some subtle cases in harmonic problems with eddy currents where you
really do have to limit the integration area to just the coils to get the
"right" results.
For inductance via the B.H integral, however, you have to integrate over the
whole model. I wasn't really clear about this in the example--sorry.

> Has anyone found a good source of magnetic data for stainless steels
> (other than MatLab)?
> Regards
> Jim Bloor

Try http://www.cartech.com/ Carpenter sells stainless that is specifically
meant for specialty magnetic applications, and you can get very detailed data
sheets from them. I think that you can obtain the data sheets from their
website, although you have to answer some questionaires to get to them.
Dave Meeker
--
http://members.aol.com/_ht_a/dcm3c

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