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# Re: [FEMM] How do I model a multiple turn copper wire coil?

- To: Finite Element Method Magnetics mailing list <femm@list.foster-miller.net>
- Subject: Re: [FEMM] How do I model a multiple turn copper wire coil?
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Tue, 21 Oct 2003 00:06:08 -0400
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`Mike Middleton wrote:`

> `I'm a real new user to FEA and magnetic modeling. I DO have a lot of experience in designing and winding transformers, via a hand calculator, pencil, and paper. Most of my work has been in RF and switching power supplies.`
> `I have done Examples 1 and 2 of the FEMM Tutorial and have an idea of what's going on.`
> `I've been asked to re-design/analyze a magnetic sensor. This sensor is basically a steel cup about 1" diameter by 1" height. The center post is an Alnico 8 magnet about 0.375" diameter. A few hundred turn copper wire coil is wound around the magnet.`
> `Of concern, is the electrical output we get from the coil as a piece of steel is passed across the open end of the sensor. I think I can figure out how to model the steel cup and magnet in FEMM.`
> `How do I model/enter the multiple turn wire coil? Modeling it turn-by turn will take a LONG time.`

`
You typically don't have to model each individual turn in a coil (unless, perhaps, you are trying a brute-force solution for proximity effects in a winding). Multi-turn coils are typically represented as a homogeneous area with either an even current distribution assigned to the region where the current density is chosen to be the Amp*Turns in the coil divided by the bulk area of the coil, or as a homogeneous region with a "current property" assigned to the region that forces to the total current in the region to be the desired number of amp-turns. An example in which a wound coil is represented in this way is http://femm.foster-miller.net/examples/induct1/induct1.htm`

    Dave.
    --

`David Meeker
Senior Engineer
Foster-Miller, Inc.
350 Second Avenue
Waltham, MA 02451-1196
781-684-4070
781-890-3489 (fax)
dmeeker@foster-miller.com`
``

- References:
  - [FEMM] How do I model a multiple turn copper wire coil?
    - From: Mike Middleton <mike@wirebenders.com>

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