Halbach array

From Free net encyclopedia

A Halbach array is a special arrangement of permanent magnets which augments the magnetic field on one side of the device while cancelling the field to near zero on the other side. In the diagram, the magnetic field is enhanced on the bottom side and cancelled on the top side (a one-sided flux). The pattern (on the front face; left, up, right, down) of permanent magnets can be continued indefinitely and have the same effect. It is roughly similar to many horseshoe magnets placed adjacent to each other, with alternating polarity.

The effect was discovered by Mallinson in 1973, and described as a 'magnetic curiosity' although he recognized that this magnetization pattern could make significant improvements in magnetic tape technology. Mallinson showed that any magnetization pattern in which the x and y components of the magnetization are <math>\pi/2</math> out of phase will cause a 'one-sided' flux, the simplest being <math>\sin(kx)</math>, <math>-\cos(kx)</math>. It was later (and independently) discovered by Halbach, who used the arrangement in particle accelerators.

This device is the fundamental principle behind the Inductrack maglev system, a levitating train that requires no power to levitate; power is only used to create forward motion. The Halbach arrays repel buried loops of wire after they have been accelerated to speed, lifting the train.

Halbach arrays were originally developed in a cylindrical shape, known as the Halbach cylinder.

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