SOMETIMES the only answer to a problem is to rise above it, and that turns out to be as true in the micro-world as it is in everyday life.
As the microscopic machines known as microelectromechanical systems (MEMS) get ever smaller, conventional methods of building them become ineffective. That鈥檚 because the forces of friction and adhesion, which have no more than a minor impact on devices on the macro scale, become a major problem at the micro level and can have a devastating effect.
If microscale objects such as tools and scalpels could be held above the work surface using magnetic levitation, friction and adhesion would no longer be a problem. The trouble with this idea is that while maglev technology can be highly successful when applied to large objects like trains, it cannot be easily controlled on smaller scales. All objects wobble around slightly when levitated, but small objects wobble much more, making it virtually impossible to accurately control their movement.
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鈥淎ll objects wobble slightly when levitated, but small ones wobble much more鈥�
Caglar Elbuken, a mechanical engineer at the University of Waterloo in Ontario, Canada, guessed that stray electromagnetic fields from the current running the electromagnets, from nearby computers and even from the lighting in the lab were probably the source of the problem. The forces arising from the magnetism that these fields induced in the objects would become dominant at the microscopic scale, Elbuken figured, causing the objects to wobble. When he studied an object levitating under a series of electromagnets, he found that as he had predicted, extraneous fields made the object wobble around.
To alleviate the problem, he placed a variety of conducting aluminium discs below the levitating object (Journal of Physics D: Applied Physics, vol 39, p 3932). These discs absorbed the stray electromagnetic fields, damping down the troublesome wobble. When Elbuken and his colleagues tested the dampers on a macro scale, using a levitating magnet 5 millimetres in diameter and 2.5 millimetres high, they proved highly effective. With a disc 4.5 millimetres thick, the levitated object was much more stable and when the thickness was increased to 9 millimetres the wobble virtually vanished. Elbuken hopes his finding will open the way for maglev technology to be used in micro-engineering.
