A Halbach array is a special arrangement of permanent magnets (or electromagnets) which augments the magnetic field on one side of the device while canceling the field to near zero on the other side. In the diagram, the magnetic field is enhanced on the bottom side and canceled on the top side. 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.
They were originally invented for use in particle accelerators by Klaus Halbach, a retired Lawrence Berkeley National Laboratory physicist. 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 ring shape, which can provide levitation for a rotating flywheel or motor shaft
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