World's 'smallest steam engine' built in Germany

The world's smallest working "steam engine" has been built in Germany, according to a team of researchers.

The microscopic model was based on a 195-year-old design by the inventor Robert Stirling.

Changes included the replacement of the original pistons with a laser beam.

The physicists said they were "astonished" by how efficiently the machine converted heat into power - but said it did "not run smoothly" and had no practical use in its current form.

A conventional Stirling engine has a cylinder of gas attached to a heat source at one end and a cold source at the other.      Read Here