The 200-year-old Stirling engine has inspired a power generator made of a single particle just 3 micrometres wide.
Overshadowed by its steam and internal combustion brethren, the Stirling engine is a quiet, efficient alternative that compresses a fixed amount of gas inside a cylinder.
As it is compressed, the gas heats up and expands, pushing a piston, before cooling due to the loss of energy, only to be compressed again.
In their tiny mimic, Clemens Bechinger and Valentin Blickle at the University of Stuttgart, Germany, replaced the cylinder with a laser that confines the motion of a 3-micrometre-wide lump of melamine in water.
A zap of heat from another laser builds up tension in this optical "trap": like a compressed gas, the particle is aching to break free. Widening the trap by modifying the first laser lets it do so, expending the pent-up energy.
"The use of a laser source to provide the required rapid localised heating on the microscopic scale appears to be novel," says Alan Tucker, leader of the Stirling Cycle Research Group at the University of Canterbury in Christchurch, New Zealand. He calls the technique sophisticated but says that he "struggles" to envision any practical applications.
But Bechinger says that the microscopic engine is allowing his team to investigate the balance between maximum power and maximum efficiency on the nanoscale – which could in turn inform the design of future micromechanical machines.
Journal Reference: Nature Physics, DOI: 10.1038/nphys2163
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