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Technological Design - Magnetic Levitation

Magnetic levitation (sometimes called maglev or magnetic suspension) is a method by which an object is suspended with no support other than magentic fields. Magnetic pressure is used to counteract the effects of gravitational, and any other, accelerations.

Earnshaw's theorem proves that, using only static ferromagnetism, it is impossible to stably levitate against gravity, but servomechanisms, the use of diamagnetic materials, superconduction, or systems involving eddy currents permit this to occur.

In some cases the lifting force is provided by magnetic levitation, but there is a mechanical support bearing little load that provides stability. This is termed pseudo-levitation.

Magnetic levitation is used for maglev trains, magnetic bearings, and for product displaying purposes.

Direct Diamagnetic Levitation

A substance that is diamagnetic repels a magnetic field. All materials have diamagnetic properties, but the effect is very weak, and is usually overcome by the object's paramagnetic or ferromagnetic properties, which act in the opposite manner. Any material in which the diamagnetic component is strongest will be repelled by a magnet.

Earnshaw's theorem does not apply to diamagnetics. These behave in the opposite manner to normal magnets owing to their relative permeability of μr< 1 (i.e., negative magnetic susceptibility).