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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: "Robert Macy" <macy@california.com>
- Date: Thu, 12 Sep 2002 08:53:49 -0700
- Organization: AJM Electronics
- References: <alq51l+v98c@eGroups.com> <3D80AB0B.60004@ieee.org>
- Reply-to: "Robert Macy" <macy@california.com>

    That explains it! I did indeed have unbounded boundary conditions.

    - Robert -

    ----- Original Message -----
    From: David Meeker
    To: femm@yahoogroups.com
    Sent: Thursday, September 12, 2002 7:56 AM
    Subject: Re: [femm] Determining inductance per meter with 2D analyses

    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>

- References:
  - Determining inductance per meter with 2D analyses
    - From: "gopherlid" <macy@california.com>
  - Re: [femm] Determining inductance per meter with 2D analyses
    - From: David Meeker <dmeeker@ieee.org>

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