The world’s smallest heat engine just demonstrated that what works for big things also works for small things -– validating an important piece of physics and maybe pointing the way to new kinds of microelectromechanical systems.
A heat engine, also called a Stirling engine, uses the temperature difference in a fluid to drive a piston. In the simplest configuration, the fluid (or gas) is heated and expands, driving a piston. As the gas expands it cools, the piston compresses it, and the gas is moved past a heat exchanger, which starts the cycle again. Stirling engines are used in a variety of industries, notably as heat pumps in refrigeration and in more modern renewable fuel power plants.
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In this case, a team led by Clemens Bechinger, professor at the University of Stuttgart and Fellow of the Max Planck Institute for Intelligent Systems, and his colleague Valentin Blickle, built a Stirling engine only a few micrometers across, using a tiny plastic bead floating in water.
Instead of a physical piston in a cylinder, the physicists used a laser beam with variable intensity. The optical forces of the laser limited the motion of the plastic particle, just like the compression and expansion of gas in the cylinder of a large Stirling engine. The particle then does work (meaning it transmitted a force over distance) on the optical laser field. An old-fashioned steam engine of this type would use coal or wood to heat the fluid, but this team used a laser beam instead. The whole system coos whenever the laser is switched off.
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The results show that tiny Stirling engines could be built and work reliably for delivering mechanical motion when an external power source can be used.
Image: Fritz Höffeler / Art For Science
Tags: Materials Science, Physics
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