Magnet moving over surface creating levitation

[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?

 

[davenn]

hi there
welcome to PF

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?

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

A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side.[1] This is achieved by having a spatially rotating pattern of magnetisation.

The rotating pattern of permanent magnets (on the front face; on the left, up, right, down) can be continued indefinitely and have the same effect. The effect of this arrangement is roughly similar to many horseshoe magnets placed adjacent to each other, with similar poles touching.

Dave

 

[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!

 

[OmCheeto]

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!

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.

A New Approach for Magnetically Levitating Trains --- and Rockets [llnl.gov]
June 1998
Inductrack
​

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.

Inductrack III for superefficient leviation and movement of shipping containers [Next Big Future]
May 19, 2013​

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​