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.
Pent-up particle
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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