Make a levitating Plate?

[tspree15]

Hello,

I'm sorry if this is a stupid question but I am trying to find out if it is possible for me to make a levitating dinner plate. Do you guys have any input on what I would need and if it is indeed possible?

Thanks so much

 

[MagMike]

Hello tspree15,

It'd be a difficult thing to do. Were you looking to do this as some sort of display, or were you planning on using them during a meal?

There are displays where an object (containing an embedded strong permanent magnet) levitates between the poles of a carefully controlled electromagnet. A sensor is constantly monitoring position and adjusting the electromagnet to keep the object rotating. I've seen displays containing a globe, a picture frame, even a gym shoe. While the effect is quite striking, the objects to be levitated need to be very lightweight. I wouldn't think they'd be suitable for supporting a dinner plate with food on it.

On the other hand, take two ring shaped permanent magnets with a (non-magnetic) pole running through the inside diameters. Position the ring magnets in repulsion and attach the dinner plate to the upper ring. With a rare earth magnet one could support quite a bit of weight, but the effect isn't as striking, and the balance may be an issue.

Hope this helps!

 

[UKpete]

tspree, sorry to go all technical on you but according to Earnshaw's theorem it is not possible to have stable levitation without having either:

1. at least one axis that is mechanically constrained

or

2. at least one axis being active (i.e. an electomagnet controlled in a closed loop system, which will require a position sensor).

An example of 1. would be that it is possible to have vertical suspension by repulsion of two permanent magnets(one on the table, the other on the plate, as described by MagMike), but with a some form of mechanical restraint to stop the plate moving sideways in any direction.

An example of 2. is a magnetically levitated vehicle.

Earnshaw's theorem isn't really intuitive (you might think that you can stop the plate moving sideways with another set of magnets), but it is real and proven mathematically.

 

[Maui]

UKpete, how is this theorem consistent with the observation that a magnetically permeable material can be levitated in a stable manner over a superconducting magnet that has been cyorgenically cooled? I have seen this myself. I purposely touched the sample to disturb it, and observed that instead of falling away it went right back into position over the magnet.

Maui

Constants aren't; variables won't.

 

[UKpete]

Maui, good point - I have seen the pictures myself. Apparently it is to do with circumstances where the inverse square law of distance on repulsion doesn't apply. Superior minds to mine have been applied to the problem so it is better to read them directly, e.g.

http://www.davidwyatt.me.uk/maglev/

- who states that for superconducting and paramagnetic materials Earnshaw's Theorem doesn't apply.

 

[UKpete]

- sorry I mean to say diamagnetic not paramagnetic.

 

[sreid]

See this Link.

http://www.rare-earth-magnets.com/magnet_university/magnetic_levitation.htm