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# [FEMM] How do you interpret inductance values? And predict inductor Q?

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- Subject: [FEMM] How do you interpret inductance values? And predict inductor Q?
- From: "robert Macy" <macy@california.com>
- Date: Fri, 21 Nov 2003 13:28:56 -0800
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    How do I interpret inductance values?  And predict inductor
    Q?

    I'm using 2d to draw a cross section of copper going
    through core material.  The core material has an
    appropriate gap to prevent saturating the core material.

    The core material has permeability and is conductive.

    The copper is included in "circuit" which sets total
    current.  The current is set to a positive value.

    I use the integral A.j over the copper area to find the
    inductance.  The answer comes back with a value of uH close
    to the value expected, but has a "loss" term of -j which
    represents resistive losses. The ratio of inductance to
    losses predict a Q of around 4, seems very low.

    Investigating where these losses originate, I find there
    are substantial eddy currents in the core material.
     Drawing a line from across the core produces and plot of
    Js + eddy current produces a plot which shows there is a
    real negative value of current and an imaginary component
    of current.  The real value is negative meaning that it is
    coming back into my face with the imaginary part doing the
    same but 90 degrees out of phase.

    This is impossible?!  The core material is finite in length
    and unterminated.  The current has no place to flow,
    therefore cannot exist.  Is this assumption correct?

    How do I predict the Q of this inductor?

                - Robert -

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- References:
  - Re: [FEMM] How does femm handle coercivity and core losses?
    - From: David Meeker <dmeeker@foster-miller.com>

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