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# [femm] Re: Problems with non-linear B-H-curves

- To: femm@egroups.com
- Subject: [femm] Re: Problems with non-linear B-H-curves
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Wed, 10 Nov 1999 08:39:44 -0500
- Delivered-to: listsaver-of-femm@egroups.com
- Delivered-to: listsaver-egroups-femm@egroups.com
- Mailing-list: contact femm-owner@egroups.com
- Organization: Foster-Miller, Inc.
- References: <3.0.6.32.19991110133237.0079e100@pop.xphys.tuwien.ac.at>
- Reply-to: femm@egroups.com

    Kuepferling Michaela wrote:

    > In our group at the Vienna University of Technology we measure magnetic
    > materials with magnetic pulse fields. I wanted to compare a
    > hysteresis-measurement of a Ni-sphere with a radius of 4.85mm with the
    > results of FEMM. The following questions arised: I got with FEMM B~8.3T
    > inside the sphere (see the attached file NiBr2.EMF). But with the applied
    > field of ~5.2T and J(Ni)~0.6T, when Ni is saturated, B becomes about 5.8T.
    > Why is the calculated B so high? The other problem is, that we expected a
    > decay of B inside the sphere because of the induced eddy currents. But with
    > FEMM I found an increase of B with decreasing radius (see the attached file
    > NiBrki.EMF).
    > I welcome any comments!
    > Michaela Küpferling

    It's hard to tell what is going on w/out seeing the .fem file that led to the
    results. Could you send it to me (perhaps just to me at dcm3c@aol.com)?

    Anyhow, one thing to remember is that although magnetostatic problems can use a
    nonlinear B-H curve, the harmonic solver is limited to linear materials properties.
    For harmonic problems, it just uses the values for linear permeability entered in the
    mu_r and mu_z boxes in the Material Property dialog. At some point,I might kludge in
    support for nonlinear materials in harmonic problems, but the problem is that a
    nonlinear harmonic formulation probably wouldn't be that accurate -- for nonlinear
    materials, you don't get a purely harmonic response from a sinusoidal applied current
    or field.

    Dave.
    --
    http://members.aol.com/dcm3c

- References:
  - [femm] Problems with non-linear B-H-curves
    - From: Kuepferling Michaela <kuepfer@xphys.tuwien.ac.at>

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