# Magnetic levitation using alternating current

## Main Question or Discussion Point

Hi, I have a few questions regarding magnetic levitation achieved by using alternating current to induce eddy current on a non-ferromagnetic conductor plate to provide the levitation force.

1. Can it be stabilized? If yes, in what ways?
2. Are there any equations/formulae or ways to calculate the levitation force provided by eddy current in this case? Which physics laws and equations should I apply in this case? (Except Faraday's and Lenz's law)
3. Is there a direct relationship between the frequency of alternating current and levitating force?

I've looked up the Internet for the whole day but still could not find an answer, your help is appreciated.

Also, I'm planning to use this as my extended essay topic, is this appropriate? (Extended essay is a 4000-word research paper that has to be completed in the IB Diploma)

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Simon Bridge
Homework Helper
Welcome to PF;
you have "looked up the internet"... what did you find besides "not the answer"?
i.e. where did you look? What sort of search terms did you use?

But you may be having trouble due to inexact terms.
1. what do you mean by "stabilized"? Do you mean - can you get a constant force from an alternating current? Then no. You ca try to adjust the current to multiple magnets to smooth out the bounces though.

2. yes. same equations and formulas as calculating any eddy current - you can find these online. Other equations would include Newton's laws of motion.

3. yes and no - the magnitude of the force depends on the current and the current varies so the force varies - but the object may still levitate for the same reason you can keep a ball in the air by repeatedly hitting it with a paddle or a racquet so you can work out an effective force off the averages. i.e. say you drop a small stone onto a paralell beam balance so it bouces off - the balance deflects and returns. If you do it regularly, then you can end up with a continuous deflection and read the balance to find the effective weight (force) the repeated impulses are delivering.

Are you at the 16 or 19yo end of the diploma?
Why not rig up an AC electromagnet and try to levitate something with it and see what happens?

Hi Simon,
I have been using keywords such as 'magnetic levitation using ac' and 'eddy current magnetic levitation'. I could not find any article about ways to stabilize it (ensuring that the levitated object does not flip into a configuration where flip is neutralized).

I am currently at IB1 (18 yo) and having my exams next May.& yes I am definitely going to try levitating a metal block with electromagnet and see if it works!

Thank you for your help. :D

mfb
Mentor
In general, passive systems are unstable - you need an active control mechanism (something that measures the position and adjusts current accordingly), spin, or superconductors to make it stable.

Simon Bridge
Homework Helper
I could not find any article about ways to stabilize it (ensuring that the levitated object does not flip into a configuration where [lift] is neutralized).
Now I get you. There are many online sources discussing this. i.e Wikipedia comments on several ways to promote stability. You may want to look up "electrodynamic suspension"

Thank you mfb, Zoki and Simon for your replies.

Since my Research Question is "What is the effect of conductivity of metal on the levitating force produced?" I think I should focus on the ways to calculate the magnitude of eddy current induced in the conductor plate since it is affected by the conductivity of metal, and then relate the magnitude of eddy current to the levitating force produced. I am measuring the levitating force using a spring balance. Am I on the right track?

As for stabilization, I might still be able to conduct the experiment to compare the levitating force using different metals without stabilizing the system, I'll see.

For your information, below is the diagram of my experimental setup (I am yet to conduct the experiment on Monday to see if it works)

I'm sorry if my questions sound very garbled because I'm a beginner in writing this kind of research paper. Once again I truly appreciate your help :)

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Simon Bridge
Homework Helper
You can investigate levitation force using mechanical stabilization. You may have to make several attempts... this is normal.

The spring balance setup seems ok. The levitating force would show as a reduction in apparent weight.
You may have to deal with the case that the force us greater than the weight though.

Would you expect the force to change with distance from the magnet?

I think I should focus on the ways to calculate the magnitude of eddy current induced in the conductor plate...
You shouldn't. That's bloody difficult. Tricky even with adequate electromagnetic software.

You can investigate levitation force using mechanical stabilization. You may have to make several attempts... this is normal.

The spring balance setup seems ok. The levitating force would show as a reduction in apparent weight.
You may have to deal with the case that the force us greater than the weight though.

Would you expect the force to change with distance from the magnet?
Yea I can't wait to try out the experiment on Monday. If the force is greater than the apparent weight, I will have to think of a different way to measure the force tho..

The force might change with the distance from the magnet, since magnetic field strength decreases with distance. I'll try it..

You shouldn't. That's bloody difficult. Tricky even with adequate electromagnetic software.
I see. I will have to find a way to explain the physics principle involved in that case without involving the calculation then. Hopefully it works..

Simon Bridge
Homework Helper
One way to deal with force being bigger than weight is to increase the weight.

mfb
Mentor
Or to reduce the currents and therefore the force.

Hi, I did my mini experiment in school today and I did not quite work.

I'm not sure about the levitating part as I could not do it due to a lack of soft iron core, but my experiment to determine the conductivity of metal blocks failed. The voltmeter reading was too low (about 0.3V) compared to the emf (1.3V), and it kept fluctuating. I might have to change the metal blocks to metal sheets, and even wire if it's still not working. I'm not sure if I could levitate a wire tho..

Seems like there's a long way to go before I even start levitating objects O___O