A laser powered micro engine has been created by researchers at the University of Stuttgart and the Max Planck Institute for Intelligent Systems.
The engine is a prototype for future micro-scale engines that could produce useful work. Its dimensions in micrometres, the Institute's and University's physicists replaced the heat source found in a normal engine, fuel combustion, with a laser beam. The laser’s intensity is varied, heating the engine from the outside and then allowing it to cool.
Clemens Bechinger, a professor at the University and fellow of the Institute said: ‘We’ve developed the world’s smallest steam engine, or to be more precise the smallest Stirling engine, and found that the machine really does perform work.’
In the heat engine invented almost 200-years ago by Robert Stirling, a gas-filled cylinder is periodically heated and cooled so that the gas expands and contracts. This makes a piston execute a motion with which it can drive a wheel, for example.
The working gas in the Stuttgart micro-engine is not gas at all but water. A plastic bead measuring three micrometres floats in molecules of water and the laser heats them propelling the bead. However the laser’s heating of the water molecules can effect movement in them that interferes with the action of the bead. This is because the bead is colliding with some of the water molecules as it moves. This can make the engine sputter and can even bring it to a stop.
According to the physicists they were astonished that the machine converts as much energy as it did per cycle and that it even runs with the same efficiency as its real-life normal size engine counterparts.