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# Re: [femm] Determining inductance per meter with 2D analyses

- To: femm@yahoogroups.com
- Subject: Re: [femm] Determining inductance per meter with 2D analyses
- From: David Meeker <dmeeker@ieee.org>
- Date: Thu, 12 Sep 2002 10:56:11 -0400
- References: <alq51l+v98c@eGroups.com>
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0.0) Gecko/20020530

`gopherlid wrote:`

> `Anybody have an idea how to calculate inductance per length?`
> `I tried using the formula 1/2 L I^2 = Energy`
> `but the Energy value changed too much based upon number of nodes. We're talking 100% It's as though, more nodes, more energy with no
> asymptotic limit in sight!`
> `It's a very simple structure, a wire with a slab of metal around it,
> so the results should be straight forward. However, the "magnetic
> field energy" seems to relate to the number of nodes *and* the number
> of nodes in the metal, which makes no sense, since there is less than
> 0.01% energy in the metal. But changing the nodes in the metal
> actually made the inductance change by a factor of 2:1`
> `Any ideas? Plus ideas on how to know when enough is enough?`
> `- Robert -`

`
It sounds like problem that you are trying to solve is ill-posed. The inductance of a single wire in an unbounded 2-D space is infinite. The result that you get when you try to analyze this problem then strongly depends on how you truncate the solution domain. To get a configuration with a bounded inductance, all of the current in your domain must add up to zero, or you must model a domain where the existence of the return wire is implied your the choice of boundary conditions.`

    There are some examples that could be relevant to you at:
    http://femm.berlios.de/induct1/induct1.htm
    http://groups.yahoo.com/group/femm/message/347

    Dave.
    --
    David Meeker <http://femm.berlios.de/dmeeker>

``

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