I am just wondering how do you differentiate the effect of self inductance vs. eddy current in FEMM? At 10 - 100Hz, I would think that the self inductance is the one to consider.
Keith Gregory <k.gregory@xxxxxxxxxxx> wrote:
At 15:31 24/10/2002 +0000, you wrote:
>--- In femm@xxxx, Keith Gregory <k.gregory@xxxx> wrote:
> > Mike,
> >
> > I think you would find that static finite elements models with
>single
> > valued magnetization characteristics would give pretty good
>approximations
> > of field distribution and winding inductances in the 50-60Hz types
>of
> > applications where the materials are laminated. Although
>calculating
> > inductances in saturated conditions is complicated. Loss
>calculations even
> > at 50 or 60 Hz are not as straightforward. Operating in Khz I
>really have
> > no idea how good results would be.
>
>
>A basic model LVDT model using mumetal core at even 100 Hz shows
>pronouned skin effect. At 5kHz there is a danger of saturation near
>the material surface at normal drive levels.
The 5kHz doesn't surprise me but the 100Hz does, although mumetal is
different to the materials I would normally work with.
> >
> > >I am currently interested in trying to observe Barkhausen noise for
> > >NiFe materials. I expect to use up to about 100 Hz field for this,
>and
> > >believe that the spectrum of the noise will contain much
>information,
> > >if it can be unravelled; early days yet. Comments are very welcome
> >
> > The classic demonstration of Barkhausen jumps is done with "DC"
> > magnetization, usually with a permanent magnet. I have a vague
>memory of a
> > paper describing a different way which can produce noise displays
>on an
> > oscilloscope. I'm not sure what information it would contain
>though, what
> > had you got in mind?
>
>
>I hope to use LF ac to cycle the jumps and give larger noise output.
>Literature suggests that Barkhausen noise can indicate heat treatment
>and internal stresses, inter alia; as properties of cores are
>affected by handling stresses I believe BN can provide an insightful
>tool into known quality issues.
I could see that, since Barkhausen noise has been attributed to sudden
domain wall movement and some people say that it is impurities and voids in
the material that make the walls stick, the amount of noise could give an
indication of the material structure and quality.
It would be interesting to see if it really is "noise" or it has some
pattern during repeated cycles.
> > In addition, if my memory serves aren't there several different
>Radiomental
> > alloys differentiated by a number such as Radiometal 36?
>
>
>Yes. The 36 refers to % nickel in the alloy. Varoius types give
>different permeability / resistivity / cost materials for different
>applications.
Keith.
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