The high-pitched buzz makes your ears hurt and permeates the entire lab at ETH's Power Electronics Systems Laboratory. A testing bench holding a mini-motor is standing on the worktop. At the press of a button the rotor of this tiny device has just reached a half a million rotations per minute, in fact it has done even more. "The shrill noise is a result of the strain on the ball-bearings," says Christof Zwyssig, PhD student at the Power Electronics Systems Laboratory. From the floor, he picks up a wooden case made from thick planks and uses it to cover the test bench. If the little motor were to fly apart, the rotor would shoot through the lab like a missile, at around 150 metres per second–nearly half the velocity of sound.

Miniature from costly material

Looking at the tiny device, it is difficult to believe. The rotor is not much thicker or longer than a matchstick, the stator half the size of a thumb. The little balls of the rotor's ball-bearings are so small that they can hardly be grasped between thumb and index finger. The inside of the stator is coated with a special copper layer. Magnets consisting of samarium and cobalt are embedded in the rotor. These materials are expensive but have the advantage of making the magnets stronger than ferrite does. The coating of the rotor made out of of titan, also has to withstand the extreme strain. The whole system is steered by digital, high performance electronics constructed by students. The steering system fits into a cigarette box.

The ETH engineers caused a sensation at the end of February with their new motor. The mini drive system that runs at a speed of 500,000 revolutions per minute, eclipses conventional industrial systems, and sets a new world record (1).

From portable energy source to dentist's drill

The project was started with the mechanical engineers, says Zwyssig. A mini electric generator as a portable source of energy is the first application. This will follow the classic conversion of chemical to electrical energy. A gas turbine, also miniaturised, powers the electric motor and with its high rate of rotation the system delivers around 100 watts of power for 10 hours. This system will be used as an energy source for mobile applications. "We are thinking about an alternative to conventional batteries," says Zwyssig. The level of energy provided by the system with regard to its weight or volume is up to ten times more than traditional batteries.

Closer inspection reveals that the ETH engineers have further ideas for its areas of application. Materials processing, for instance, could make good use of small motors with such high rotations to power a drill. The drills become ever smaller and finer, within a micro-meter scale, and must thus be able to rotate even faster in order to reach their aim at the same level of productivity.

Such rapidly rotating tools are also in demand in dentistry. No wonder the excruciating sound of the motor calls to mind the shrill scream of the dentist's drill. Here, drills are employed that reach 200,000 rotations per minute, or even 400,000 when driven by air spindles.

Application at 12,000 metres altitude?

Interest in the system is not confined, however, to everyday users; balloonist Bertrand Piccard is also interested. In 2009 Piccard has plans to fly non-stop round the world with a solar plane for the Solar Impulse Team (2).

Came up trumps: electro-engineer Christof Zwyssig with the components of the new ultra-rapidly rotating motor system. Left the steering electronics, right the rotor and the thumb size stator. large

For the construction and equipment of the cockpit–the plane should be able to climb to 12'000 metres–the most modern technologies are required, amongst other things for pressure equalisation in the cabin. The ultra-rapid rotating motor system could come in handy here.

In the meantime, it has quietend down, again, in the lab. The motor stands still. The scientists still have to do something about the noise. "It might be possible to lower this with a magnet or air cushion instead of ball-bearings," says the PhD student. If the young engineer wants to break into the dentistry instrument market, he will first have to come to grips with the noise problem.

With an eye on more records

18 months of Christof Zwyssig's PhD studies have now passed, during which time he has worked exclusively on the ultra-rapid motor. This is only an intermittent step. He has already set his eye on the next goal: a propulsion system that can reach a million revolutions per minute. "This is the next boundary to reach," says the electrical engineer.

To reach this goal he cannot merely accelerate the control of the existing system. The rotor must be made more stable in order to withstand the extreme centrifugal force that is caused by such high rotation. This is why he needs a new rotor construction, he says. The material also had to undergo more tests. A key element in this further increased speed of rotation is the bearing. Here new concepts, like magnet or air cushions, which the young graduate is currently studying, should help. Zwyssig is already convinced that, " it will be an entirely new machine," He thinks it will take around two years to develop. His graduate studies will then reach their conclusion–and the transfer of technology (and the corresponding brain power) will just be beginning.