# Magnet moving over surface creating levitation

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1. Nov 23, 2015

### vidur27

Hi,

I've been doing reading on Halbach Arrays moving over surfaces and generating repulsive forces. From my understanding, the moving magnet induces a circular electric current in the metal track, which gives rise to a magnetic field.

However, I'm having trouble understanding why this field causes the array to levitate. Why doesn't the array become attracted to the sheet?

2. Nov 23, 2015

### davenn

hi there
welcome to PF

Im not sure what you are describing is really a Halbach Array. Have you read the wiki article ?

https://en.wikipedia.org/wiki/Halbach_array

Dave

3. Nov 23, 2015

### vidur27

Sorry, I was on my phone, I should be a little more detailed.

There exists a system called the Inductrack where they essentially move a halbach array at a velocity over a track. This induces circular eddy currents in the track, which in turn produce an upwards magnetic field. In theory, the upwards magnetic field causes the halbach array to levitate over the track. Because the strength of the field is proportional to the strength of the current which is proportional to the rate of change of magnetic flux from the array over time, the faster the array moves over the track, the greater the levitative force will be.

My question is a fundamental one. So we induce eddy currents in the track, which gives rise to eddy currents, which gives rise to a magnetic force in the "upwards" direction. Why is this force a cause for levitation (repulsion) and not attraction? Is it a consequence of Lenz's Law? I'm having trouble seeing it!

4. Nov 23, 2015

### OmCheeto

Interesting. I have no idea how it works.
It appears to have been invented at the Lawrence Livermore National Lab.
Here's an article dated 1998.
There have been a few discussions about it here at PF. I don't see anywhere that anyone thoroughly explained the effect.

It appears to still be in the testing phase.

The original patent:
Magnetic levitation system for moving objects [google patents]
US 5722326 A
publication date March 3, 1998​

Here's a paper by the inventor, Richard Post:
The Inductrack Approach to Magnetic Levitation
POST, Richard F., RYUTOV, Dmitri D.
Lawrence Livermore National Laboratory​