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Creating a magnetic ring field question

by oliver102
Tags: fields, levitation, magnetic, magnets, ring
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oliver102
#1
Jun17-11, 04:19 AM
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Hi there,

I'm attempting a science experiment to create a magnetic suspension field that can hold magnetic objects in place in mid air.

Since a Magnetic field isn't flat a single magnet would be pointless as the opposing object is continually sliding off it, so I looked at creating a ring field so that objects would get caught in a magnetic trap as gravity acted down on them.

I'm wanting to build a large one that can hold something substantial however I want to build a prototype first to make sure my little theory works.

The design for it is relatively simplistic, a disk of wood with a uniform sequence of holes in 3 rings going round it.

The magnets them selfs are neodymium rod magnets dropped into the housings so they are fixed, each one is 2mm wide and 8 mm long. I'm still calculating the spacing in order to generate the magnetic ring needed to apply 360 degree's of magnetic force to be able to hold something stationry as I know a single weak spot will cause it to collapse.

Anyone have any thoughts on improving this little experiment?

I studied maths not physics, magnetic fields are just something that fascinate me and I'd like to do some experiments with their applications.

Thanks
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f95toli
#2
Jun17-11, 05:44 AM
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It can't be done (unless you use a diamagnetic materials, such as superconductors).
There is even a theorem proving this: http://en.wikipedia.org/wiki/Earnshaw's_theorem
oliver102
#3
Jun17-11, 06:09 AM
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Can you suggest a Diamagnetic material that would work?

Just so I understand it, a common permanent magnetic field can support a diamagnetic plate cant it? Such as graphite, if dropped in a magnetic field should be suspended.

I only did a few weeks of electromechanics and didn't get to do much practical work to experiment.

f95toli
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Jun17-11, 06:22 AM
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Creating a magnetic ring field question

The only thing that would work is a superconductor; and if you use a type-II superconductor such as YBCO you don't even need a ring (due to the flux pinning).
But then you would of course need to cool it using for example liquid nitrogen or a pulse tube cooler so it is rarely a practical solution.

All normal diamagnetic materials are much too weak to support anything in the kinds of fields you can get from a permanent magnet.

Hence, there is a reason why you've never seen this in a commercial product.
Drakkith
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Jun17-11, 07:03 AM
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Could you simply design it so that the magnets holding the object up are on the bottom and it sits in the well of a couple of others on the ground? Like have a center magnet on a base, with a couple of other magnets arranged around it but tilted inwards slightly so that the fields form a "cup" of sorts. Would this work?
f95toli
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Jun17-11, 07:15 AM
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Quote Quote by Drakkith View Post
Could you simply design it so that the magnets holding the object up are on the bottom and it sits in the well of a couple of others on the ground? Like have a center magnet on a base, with a couple of other magnets arranged around it but tilted inwards slightly so that the fields form a "cup" of sorts. Would this work?
No, see Earnshaw's theorem above. It is quite literally impossible to create configuration where the object is stable.
Drakkith
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Jun17-11, 07:22 AM
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Quote Quote by f95toli View Post
No, see Earnshaw's theorem above. It is quite literally impossible to create configuration where the object is stable.
Ah ok, I see now. New suggestion: Use some kind of support or varying magnetic fields to hold it in place.


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