Creating a magnetic ring field question

oliver102

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

f95toli

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

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

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

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

No, see Earnshaw's theorem above. It is quite literally impossible to create configuration where the object is stable.

Drakkith

Ah ok, I see now. New suggestion: Use some kind of support or varying magnetic fields to hold it in place.