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# Re: [femm] How is 5 Tesla possible?

- To: <femm@yahoogroups.com>
- Subject: Re: [femm] How is 5 Tesla possible?
- From: "Robert Macy" <macy@california.com>
- Date: Mon, 13 Jan 2003 14:02:15 -0800
- Organization: AJM Electronics
- References: <avn680+1sbr@eGroups.com> <3E1F3465.4050201@ieee.org> <5.1.0.14.0.20030113140247.01dc0b20@staff-mailin.lboro.ac.uk> <000201c2bb23$45715560$497b5142@robertmacy> <3E22F6E7.6090405@plix.com>
- Reply-to: "Robert Macy" <macy@california.com>

    The MuMetal curve came in the Library section. Saturation appears to be
    near 0.6T with the slope of the last two data points having a relative mu of
    around 2.4, not 1 as true saturation would be. Note: I notice the curve is
    not "well behaved" in that it appears to be slightly "lumpy", but is
    monotonic.

    Will add points to make certain that there is no extrapolation, only
    interpolation to see what happens. However, postprocessing shows that the
    effective mu is "locked" at 89,000 (the value listed in the materials
    description) Somehow it appears that the program completely ignores
    nonlinear aspects of the material and uses a linear value completely. ??
    Or am I missing something?

    Simple problem: I am trying to find the inductance per unit length for a
    wire that is captured between two pieces of mumetal (slight air gap)

    - Robert -

    ----- Original Message -----
    From: Dave Squires
    To: femm@yahoogroups.com
    Sent: Monday, January 13, 2003 9:27 AM
    Subject: Re: [femm] How is 5 Tesla possible?

    Check the BH curve of the core material.
    Does it take into account saturation correctly?
    What is the effective mu and what effective H
    do you see in those areas?

    I find that if you get the BH curve to be extended
    into the saturation region correctly that you start
    to see the flux leakage you would expect and the
    flux density is better behaved.
    Otherwise you can see ridiculous numbers like even
    40 or 50 tesla or more. Try to put more points
    that are more realistic on the BH curve out into
    the high H regions. That should help some. Otherwise
    FEMM will just extrapolate at the previous slope
    of an unrealistic mu higher than what it should be.

    DRS

    Robert Macy wrote:
    > Just downloaded and ran it. Got 8 to 9 Teslas in the tight areas.
    >
    > ??
    >
    > - Robert -
    >
    >
    > ----- Original Message -----
    > From: Keith Gregory
    > To: femm@yahoogroups.com
    > Sent: Monday, January 13, 2003 6:11 AM
    > Subject: Re: [femm] How is 5 Tesla possible?
    >
    >
    > Robert,
    >
    > Harmonic problems (i.e. where frequency is not zero) are solved linearly
    by
    > FEMM, it doesn't include saturation so any value of B can be achieved.
    Dave
    > has recently produced a development version which can deal with non-linear
    > problems, which is (I think) currently version 3.3alpha2.
    >
    > http://femm.berlios.de/femm33src.zip
    > http://femm.berlios.de/femm33bin.exe
    >
    > Try that.
    >
    > Keith.
    >
    > At 23:22 12/01/2003 -0800, you wrote:
    >
    >
    >>Apologize for the stupidity here, but...
    >>
    >>How is 5 Tesla possible? in mumetal that saturates at 0.6T?
    >>
    >>While doing a simple analysis using mumetal I found that at 100KHz the
    >>material displayed the expected skin depth effects, but the |B| magnitude
    >>fields were more than 5 teslas.
    >>
    >>How is this possible?
    >>
    >> - Robert -
    >>
    >>
    >>
    >>
    >>
    >>
    >>
    >>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    > Dr. Keith Gregory
    > Senior Lecturer
    > Department of Electronic & Electrical Engineering
    > Loughborough University
    > Loughborough
    > Leicestershire
    > LE11 3TU
    > UK
    >
    > Phone: +44 (0) 1509 227025 Fax: +44 (0) 1509 227014
    > Department web: http://www.lboro.ac.uk/departments/el/
    >
    >
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- References:
  - Alnico 8 relative permeability
    - From: "sloothrog <salvarsan@std.com>" <salvarsan@std.com>
  - Re: [femm] Alnico 8 relative permeability
    - From: David Meeker <dmeeker@ieee.org>
  - Re: [femm] How is 5 Tesla possible?
    - From: Keith Gregory <k.gregory@lboro.ac.uk>
  - Re: [femm] How is 5 Tesla possible?
    - From: "Robert Macy" <macy@california.com>
  - Re: [femm] How is 5 Tesla possible?
    - From: Dave Squires <djsquires@plix.com>

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