How exactly does a mag trainer work (I mean its details)?

I can’t find this online and short of taking mine apart, how does the resistance work specifically? I understand the fluid ones and wind ones, but how exactly is a magnetic trainer finding its resistance? If I think of a small electric motor, the current is constantly switching back and forth so that the attraction/repulsion is always where it wants to be, but in some manner a magnetic trainer is doing the same thing. How does it do it? Has anybody got pics of one disassembled?

what brand?
does it plug in?

I can’t find this online and short of taking mine apart, how does the resistance work specifically? I understand the fluid ones and wind ones, but how exactly is a magnetic trainer finding its resistance? If I think of a small electric motor, the current is constantly switching back and forth so that the attraction/repulsion is always where it wants to be, but in some manner a magnetic trainer is doing the same thing. How does it do it? Has anybody got pics of one disassembled?

see: http://en.wikipedia.org/wiki/Eddy_current_brake
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see: http://en.wikipedia.org/wiki/Eddy_current_brakeThanks!

Regarding brand I assume they’re all pretty much the same.