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# Re: [femm] [Circuit Model]

- To: femm@yahoogroups.com
- Subject: Re: [femm] [Circuit Model]
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Mon, 01 Oct 2001 11:33:18 -0400
- Organization: Foster-Miller, Inc.
- References: <F106yQlmLFQG101s7hp0000a888@hotmail.com>

    you se-ho wrote:

    > To Dear All:
    >
    > How are you?
    >
    > Simulation (1) I define in the circuit define menu:
    > circuit 1: +1A
    > Circuit 2: +1A
    > circuit 3: -2A (so, acts return ground.)
    >
    > Simulation (2) Circuit A: +1A
    > Circuit B :-1A (this is the return ground.)
    > then I assigned the "circuit A" to two traces. And I found the
    > FEMM automatically divided the current half and half.
    >
    > I check inductance and resistive loss. I expected them same, but now
    >
    > Is there anybody knows the reason?

    I tried an example like this, except ihn your Simulation (2), I defined:
    Circuit A: +2 A
    Circuit B: -2 A
    so that the total current wold be the same in both cases. I then got exactly
    the same losses from both cases. Check out the attached examples.

    Anyhow, the only other thing that I could think of is that femm doesn't
    necessarily split the current half-and-half between the two conductors if the
    two conductors are driven in parallel as in your Simulation (2)--it would only
    split the current exactly evenly if this were dictated by symmetry
    considerations. It would also be possible to create small imbalances, even in
    a configuration that is nominally symmetric, if the mesh density is very
    coarse in the conductors. If the mesh density is very coarse, there is some
    error in fitting curved boundaries with straight-sided triangles, resulting in
    a small difference in the area between conductors. One conductor would then be
    slightly less resistive than the other, pulling slightly more current. Also,
    if you are evaluating a problem at a high frequency and you don't use enough
    elements to model the field in the skin depth region adequately, you can get
    the same sort of effect--slightly different amounts of current get carried in
    each conductor that you are driving in series, even if the model is nominally
    symmetric.

    Dave.

Attachment: `zip00020.zip`
Description: Zip compressed data

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- References:
  - [Circuit Model]
    - From: "you se-ho" <sxy28@hotmail.com>

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