Steam makes micro return

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The Independent Online
TWO HUNDRED years after the steam engine helped to spark the industrial revolution, a micro-steam engine could provide the motive power for machines that can manipulate very small objects - down to the scale of individual cells.

The micro-engine, designed and built at Sandia National Laboratories in Albuquerque, New Mexico, is made of parts smaller than a human hair. It is built on a silicon wafer with the same etching technique that is used to make computer chips.

The inventor of the micro- steam engine, Jeff Sniegowski, says it will act as a spur to promote the development of micro-mechanical devices.

'Our micro-engine works over a longer distance and with a force 100 times greater than existing small actuators, which are powered by static electricity.'

The micro-engine works on the same principle as its larger forebear - using steam to move a piston.

The steam is formed when a micro-droplet of water at one end of a tube is heated by a very fine hot-wire filament. This creates a bubble that moves along the tube. The surface tension between the water and the bubble pulls the piston along the tube.

When the water cools, a silicon spring forces the piston back. The displacement and speed of the piston can be varied by altering the voltage applied to the wire.

Surface tension is a very strong force at tiny dimensions and was previously perceived as a problem in such small devices. 'Instead of seeing it as an adversary, I decided to utilise surface tension to create a motive force,' said Mr Sniegowski.

Sandia Labs is now prospecting for companies to commercialise the micro- engine.

It is also developing a pair of micro-tweezers for use in medical or mechanical applications.

The ends of the tweezers will be smallenough to manipulate parts of cells.

Mr Sniegowski said: 'We are talking to companies about using these tweezers in micro- surgery and believe they will be useful in eye surgery.'

Because the devices are built using chip fabrication techniques, they can be made in large batches. This will make them cheap enough to be disposable.

(Photograph omitted)