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Levitating stages float loads without friction

01 December, 2002

Levitating stages float loads without friction

US researchers have developed a levitating technique for transporting sensitive items along production lines without the risk of contaminants caused by mechanical friction, and without needing the costly controls and power supplies required for active magnetic bearings.

The researchers, from California-based SRI International, have harnessed a weak magnetic phenomenon known as diamagnetism which, until recently, has been regarded as little more than a laboratory curiosity. Materials exhibiting this phenomenon include many that are not usually considered to be "magnetic", including wood, water and living animals.

Although diamagnetic forces are much weaker than those exhibited by ferromagnetic materials such as iron, they are intrinsically stable and, when used with other, more powerful, materials, can produce effects such levitation. In one famous experiment demonstrating the phenomenon, a frog was shown to "float" in the air.

In the SRI development, diamagnetic materials are used to stabilise the magnetic forces produced by conventional rare-earth permanent magnets, causing a load to "float" with an air gap of around 1mm. The inventors - Dr Ronald Pelrine and Dr Jonathan Helm - have developed both linear and rotary bearings based on the technology, which has recently been granted a US patent.

The technology (seen in a prototype version above) has also been built into a clean-room transport system for a manufacturer of magnetic storage media and this system can carry a 16kg load — claimed to be a record for a mass suspended by diamagnetic levitation.

The SRI developers see clean-rooms as being an ideal application their technology because it can replace gears, pulleys and other mechanical devices which could give off particles as a result of friction, and then transport these particles around the production area.

Although diamagnetic levitation systems are simpler and potentially cheaper than active magnetic bearings, they are not as stiff, and relatively small forces can disturb their balance. They therefore have to be tailored carefully to the application.

The SRI researchers are investigating other applications for diamagnetism and have already built a frictionless micromotor that spins at 21,000 rpm, and a levitated flowmeter with a 2,000:1 turndown ratio. They are looking for licensees for their technology.

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