Magnetic bearing
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A magnetic bearing is a bearing which supports a load using magnetic levitation.
Magnetic bearings are commonly used in watt-hour meters used by electric utilities to measure home power consumption. Magnetic bearings are also used in high-precision instruments and to support equipment in a vacuum, for example in flywheel energy storage systems. A flywheel in a vacuum has very low windage losses, but conventional bearings usually fail quickly in a vacuum due to poor lubrication. Magnetic bearings are also used to support some trains in order to get low noise and smooth ride by eliminating physical contact surfaces (see magnetic levitation).
Magnetic bearing advantages include very low and predictable friction, ability to run without lubrication and in a vacuum. Disadvantages include high cost, low accuracy, and relatively large size. In addition, it is difficult to build a magnetic bearing using permanent magnets, and techniques using diamagnetic materials are relatively undeveloped. As a result, most magnetic bearings require continuous power input and an active control system to hold the load stable. Because of this complexity, the magnetic bearings also typically require some kind of back-up bearing in case of power or control system failure.