Re: High permeabilty materials and megnetic fields

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"sekots" <u37146@uwe> wrote in message news:77b09cbcaaf31@xxxxxx
We are all familiar with the classic presentation of a solenoid with an
iron
core, in which the high permeability core magnifies the strength of the
inducted filed. What about a situation with a permanent magnet? If I
bring a high permeability material into contact with a very strong
permanent
magnet (e.g. neodymium magnet), do I get a similar field strengthening?
My
specific question regards the coupling of a neodymium magnet and a piece
of
"Mu" metal. This is a metal that supposedly has a permeability 25,000
times
that of free space at 0.002 Tesla. Does this mean that I will get a field
of
25,000 Tesla within the Mu metal if I place it in contact with a Neodymium
magnet with a surface field strength of 1 Tesla ? This hardly seems
possible.


You are right- it is not possible. You will get 1 Tesla or a wee bit less.
The permanent magnet has a core with a reasonably high permeability and some
equivalent mmf such that if the external path has infinite permeability
(better than mu metal) , the flux density is limited to, say, 1 Tesla if
that is the point on the B-H curve at 0 external mmf. A permanent magnet
works on the "backside" of the B-H curve where an electromagnet is operated
on the "frontside" but the analysis can be made as if it was an
electromagnet (mmf in series with internal and external reluctance).

There are a number of references on the web and MIT's open course ware does
have some good information. I also have some material in the form of a pdf
which I can send on direct request.
--

Don Kelly dhky@xxxxxxxxxxxx
remove the X to answer


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