Magnetic levitation using eddy current

[smokedvanilla]

Hi,
I am working on an experiment to investigate the effect of electrical conductivity of the metals on the levitating force produced.

Basically the concept is this: when a metal plate is placed on top of a solenoid (but not touching), as the a.c. flows in the solenoid the change in magnetic flux induce eddy current in the metal plate. The eddy current will flow in a direction such that it opposes the magnetic field that induces it, so a repulsive force will be produced between the solenoid and metal plate. I thought conductivity of metal would affect it as the higher the conductivity the larger the eddy current induced.

The problem here is, does paramagnetism, diamagnetism or ferromagnetism affect the repulsive force between the metal plate and the solenoid? Also, does the shape of the metal plate affect the eddy current produced within it? Can I use a flat, square metal plate to substitute metal ring?

 

[Geo louv]

Yes the shape effects current

 

[Geo louv]

Also I B distance between the two objects---effects force between the two objects

 

[Jeff Rosenbury]

The material type will affect the magnetic permeability (µ). For example diamagnetic materials often have µ<µ_º. (They are sometime anisotropic which makes µ a second order tensor.) This will of course affect your measurements.

 

[smokedvanilla]

Thank you for your replies!

Yes the shape effects current

What the does the shape of the loop in I₂ represent?

Page 2 in this link http://www.innospection.com/pdfs/Eddy%20Current%20Theory.pdf talks about eddy current in cubic/cuboid metal plate, so I deduce that metal plates are also capable of producing repulsive force against the solenoid.

The material type will affect the magnetic permeability (µ). For example diamagnetic materials often have µ<µ_º. (They are sometime anisotropic which makes µ a second order tensor.) This will of course affect your measurements.

I see. So I deduce that paramagnetic and ferromagnetic materials will be able to produce repulsive forces while diamagnetic will not? (Since the difference between ferromagnetic and paramagnetic materials is the ability to retain magnetism in the absence of external magnetic field.)

 

[Jeff Rosenbury]

No, it should still repel. The amount will vary.

For ferromagnetic material, it will attract as well. You will have to run the numbers to see which effect dominates in which material, geometry, and magnetic field.

BTW, you should read the Wikipedia pages for the different types of magnetism.

 

[smokedvanilla]

Noted. Thank you! :)

 

[Skatterbrain]

My understanding is that nonferrous metals like aluminum will levitate, but ferrous metals (steel, iron, etc.) will not. The attraction of ferrous metals to the electromagnet is stronger than the levitating force produced by the eddy currents in the plate.

From what I've read, the thickness of the plate is also important. Maybe someone can offer some insight into why that is.

As for the metals shape, I think it depends on the amount of power supplied. There is a video on Youtube entitled "Levitation Coil-Induction Heating" which shows an ingot of aluminum levitating and melting. Of course, they're pumping a huge amount of power into it.

Please don't quote me on any of this, I only have a rudimentary understanding, but I hope it helps you find your answers.

I've been tinkering with this with no success. Would like to know if you get it to work.

Cheers,

Scatterbrain

 

[smokedvanilla]

Hi Scatterbrain,



This video shows a successful magnetic levitation. He has stated that he used ~520 turns insulated aluminium wire and applied voltage of around 66V, 50Hz.

Anyway, my trial was not successful as it was too dangerous to use such a high voltage in the school science lab.

 

[Skatterbrain]

The levitating effect can be created by alternating current or pulsed dc current. I bought a pulsed dc power supply that put out 101.3 volts and a commercial electromagnet. The magnet is strong. I put it face down on a steel work bench and had a hard time pulling it off by hand. I tried using it to levitate aluminum plates of various sizes and thicknesses. It had no effect.

I've seen videos like the one you posted where a standard outlet is used. Not sure what I'm doing wrong. Most videos show a variac (variable ac transformer) being used to increase the voltage. I'm going to try that next, increasing the voltage on a coil rated to handle the higher voltage.

This is an interesting puzzle, it seems so simple and straight forward, but not so easy to do.

 

[William White]

You should check out the work of Eric Laithwaite.

His excellent series of Christmas Lectures For Children at the Royal Institution (back in the 1970s) are available on the Royal Institution's website.

I think he did the levitating effects for the James Bond film Moonraker