How Eddy Currents Produce Attractive Electromagnetic Forces-Maglev

[The Head]

How Eddy Currents Produce Attractive Electromagnetic Forces--Maglev

Hello, I am working on a paper about maglev systems and am trying to describe attractive electromagnetic suspension systems, but I am having a little trouble exactly visualizing how this works, which from what I have read is due to magnetic fields through eddy currents. In repulsive electrodynamic suspensions systems, this all makes a lot of sense to me. The changing magnetic field runs through the surface of the tracks and sets up eddy currents that oppose the time-changing flux, which in turn create a magnetic field of their own. The result of the two magnetic fields is magnetic repulsion, due to the magnetic pressure between the two systems.

But how can eddy currents be used to explain the attraction. When I draw the diagrams of magnetic fields going through a conductor, I am only able to figure out a way to draw them such that the induced magnetic field is repulsive. Can anyone help me see how they can be attractive as well? Thank you!

 

[sophiecentaur]

I may have lead a sheltered life but I have only heard of repulsive maglev systems. Do you have a reference?

 

[maimonides]

The german Transrapid system works with attractive forces.
http://en.wikipedia.org/wiki/Transrapid
But the lifting has nothing to do with eddy currents.

 

[The Head]

I was reading through several websites, though this is the one that mentioned an eddy current for attractive EMS:
http://www.hk-phy.org/energy/transport/trans_phy02_e.html

I can't vouch for the validity, and it seems like every website explains it a little differently, but the website's second diagram is good, and it is one I have seen on many sites. All in all, I am just having difficulty explaining the mechanism for induction. Anybody have a better idea than I at how the alternating current in the undercarriage of the train attracts the guideway (rail)?

 

[maimonides]

If I understand it correctly, there is iron in the undercarriage (as well as in the train electromagnets). So its a "simple" case of magnetic attraction.
I found no mention of AC for the lifting magnets. AC lifting magnets might not work with the propulsion system.
Eddy currents are used for distance sensors (according to your link, which I do not like very much) and for braking.