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# Re: [femm] Diamagnetism

- To: femm@yahoogroups.com
- Subject: Re: [femm] Diamagnetism
- From: Keith Gregory <k.gregory@lboro.ac.uk>
- Date: Wed, 06 Mar 2002 20:26:07 +0000
- In-reply-to: <a5rh0e+fnou@eGroups.com>

`I've read a few replys about this and thought I might add my bit since I have in the past tried to model diamagnetic and paramagnetic materials.`
`Diamagnetic materials have small (usually very small) negative susceptibility which means that their relative permeability is slightly less than 1. This is simple to model in FEMM because you can set the permeability to whatever you want. However, whether or not the very small differences in permeability between air and the majority of diamagnetic materials would be noticeable is questionable.`
`Note that air is slightly paramagnetic and has a relative permeability of about 1.00000034 (I think) and diamagnetic materials would tend to drive flux out of them - flux density is a little bit lower in the material than in the air surrounding.`
`Diamagnetic and paramagnetic effects are difficult to measure experimentally and are just as difficult to model. I would concur with Dave, that a very fine mesh would be required and it may be that FEMM doesn't work to sufficient significant figures to deal with the problem. What precision do you use Dave?`
`Keith.`
`At 21:42 02/03/02 +0000, you wrote:`

>     Hi All!
>     As a newby , will I be wasting my time getting to grips with FEMM if
>     I want to model diamagnetic stabilisation of permanent magnet
>     levitation? (I can't find "diamagnetic" or "susceptibility" in the
>     messages index for this group, so I guess that FEMM might not be my
>     best bet for this problem.)
>     If so, can anyone please recommend an alternative ( free ) software
>     package? I'm particularly interested in modelling the effects of
>     diamagnetics with holes in them in this problem.
>     Thanks
>     Robert Hillier

> ``
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    - From: "roberthillier" <roberthillier@yahoo.co.uk>

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