Magnetic river

Magnetic river is an electrodynamic suspension magnetic levitation (maglev) system designed by Eastham and Eric Laithwaite in 1974.

It consists of a thin conductive plate on an AC linear induction motor. Due to the transverse flux and the geometry, this gives it lift, stability and propulsion as well as being relatively efficient.^[1]

The levitation is 5 axis stable, and the remaining axis is neutrally stable, or can be biased to accelerate in either direction along the motor. Notably, laterally, it exhibits a 'river bank' effect, where moving the plate either side slightly causes the plate to rise on that side, and due to this the plate tries to return to the centre line under gravity.

Principle

In magnetic river the conductive plate is a critical width relative to the magnets underneath it.

The row of magnets for the linear motor each have two poles, with the poles arranged transverse to the 'river' with U-shaped cores, and excited with an AC current.

When energised the magnets produce an oscillating transverse field which cuts the plate. The plate then generates two eddy currents, one above each pole.

However, the edge reduces the size of the eddy current on each side, since it interferes with the circular current. Moving the plate sideways increases the current on one side, since the edge is interfering less, and this pushes that side higher. The plate then moves laterally back towards the centre under gravity, stabilising the lateral motion.

This stabilisation only works provided that the plate is not too wide or too narrow, and is also somewhat dependent on levitation height, the plate must be wider at higher lifts.

References

1. ^ http://books.google.co.uk/books?id=S0nn3r855xsC&lpg=PA805&ots=xmWu1GV7j-&dq=magnetic%20river&pg=PA805#v=onepage&q=magnetic%20river&f=false

External links

• Imperial college video of magnetic river in action

• Obituary of Professor Eric Laithwaite