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# Re: [femm] h.t integrals around a closed loop

- To: femm@yahoogroups.com
- Subject: Re: [femm] h.t integrals around a closed loop
- From: David Meeker <dmeeker@ieee.org>
- Date: Sat, 12 Oct 2002 23:19:24 -0400
- References: <ao1gr9+cqce@eGroups.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.1) Gecko/20020826

Magnets are modeled internally in femm as being like a volume of ferromagnetic material with a very thin coil of wire wrapped around the edges of it. There is a better description of this in Appendix A of the manual. When you take a H.t integration on a path through magnetic material, you end up enclosing some of the "surface currents" of the magnet, leading to a nonzero result--the field has to get driven by something. Anyhow, yhere's an OK explanation of the "surface currents" at: http://farside.ph.utexas.edu/~rfitzp/teaching/302l/lectures/node62.html
If you take a path through just air, or you take a path that really doesn't enclose any currents, the H.t integral should add up to be something close to zero--it won't be _exactly_ equal to zero, because this property is only "weakly" enforced in the formulation employed by femm. If you refine the mesh, the property gets more accurately enforced.
Dave.
cambo24680 wrote:

> `Hi
> I am new to FEMM and have created a design that is basically a ring
> of iron with an air gap in it and with one section of the iron being
> replace by a piece of magnetic material. If i do a line integral of
> h.t around a closed contour through this loop the answer should be
> zero but when i do in fact do this using femm i get a non zero answer.
> I have done a similar integral around a torus of magnetic material
> with an air gap in it and again the integral does not equal zero, why
> is this?
> i do not understand how to attach files to this e-mail so i have
> uploaded a file called ring2 with the design in. if anybody can tell
> me the best way to show you guys the deign i would be grateful.
> adam`

--
David Meeker

> ``

- References:
  - h.t integrals around a closed loop
    - From: "cambo24680" <cambo24680@yahoo.co.uk>

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