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# Re: [FEMM] modeling coils???

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- Subject: Re: [FEMM] modeling coils???
- From: David Meeker <dmeeker@ieee.org>
- Date: Mon, 29 Mar 2004 21:06:37 -0500
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`Jeff Peery wrote:`

> `Hello, I am new to using FEMM and to electro magnetism - I'm a mechanical engineer fresh out of Univ. or Washington! I have a new job and I'm jumping right into this stuff. I'm looking at modeling the field that results from a magnetric flow meter. I am pretty much following example 2 from the FEMM website; however the example shows a transverse slice of the inductor and I want to model a axial slice so I am confused about how to do this. I attached my current FEMM file.
> basicallly I have a simple inductor and I want to know what the mag lines look like. I setup the geometry, meshed it, applied material properties, and a boundary condition and ran the solution. the results don't look right. My confusion is that the flux lines should parrallel the inductor, but instead they radiate from the inductor ( in a circular fashion with the inductor at the center). so how does FEMM know how my coils are oriented? From the results it looks as thought FEMM thinks I have a transverse slice of my inductor, however what I want to model is an axial slice. Can anyone offer some advice? thanks!
> Jeff`

`
FEMM is designed to analyze 2D planar or axisymmetric geometries. Both of these types of geometries are characterized by the current flowing only in the into-the-screen or out-of-the-screent directions, and by flux flowing in the plane of the screen. You have to take a cut of your geometry where the currents and flux have this form to model your problem with FEMM.`
`If you're just learning about eletromagnetism, FEMM isn't the place to start. The place to start is with trying to understand magnetic circuit theory (which is sort of an analogy to networks of electrical resistors). The reference that I like is Martin Plonus's "Applied Electromagnetics," which is typically available as a used book for about $30. Nasar's "Schaum's Outline of Electric Machines & Electromechanics" is also good and is even cheaper. The point to this is that what FEMM is doing is essentially building a fairly elaborate network magnetic circuits through which flux can flow. Magnetic circuits will get you a long way in understanding and designing magnetic devices, and you can then understand what FEMM as an analogy to or extension of the simple magnetic circuit representation.`
`Dave.`

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