BBC:
Clemens Bechinger of the Max Planck Institute for Intelligent
Systems at the University of Stuttgart and his colleagues have
built a tiny steam engine based on the Stirling engine invented
in 1816. Bechinger and his team wanted to know if the engine's
basic
operating principle would work at the microscale. To adapt
the engine to that size, they replaced the original design's
cylinder of gas with a micron-sized particle of melamine
submerged in a tiny chamber of water. A focused IR laser beam
took the place of pistons and acted as optical tweezers to hold
the melamine in place. A second laser was used to heat the
water, which cooled back to room temperature as soon as the
laser was turned off. The micro-engine was as efficient, but
not as stable, in its energy production as a full-sized
Stirling engine. Water molecules in the solution surrounding
the melamine constantly collided with the microparticle,
causing energy to be passed back and forth. In a larger engine
the amount of energy generated makes such collisions
irrelevant, but in the microscopic engine the energy levels are
too similar. While the micro-engine isn't a practical power
source, the team's research could be used to create more stable
power sources for micromachines.
