19-09-06

US scientists have unveiled a research project that aims to manufacture microscopic engines which can generate electricity using just water or heat.
Michel Maharbiz, assistant professor of electrical engineering and computer science at the University of Michigan, and principal investigator on the project, said that the engine was inspired by the way that ferns spread spores. The device is essentially a microactuator which transforms one form of energy, in this case heat via the evaporation of water, into motion. When the cells in the outer wall of the fern sporangium were waterlogged, the sporangium remained closed like a fist, storing the spores safely inside. But when the water in the outer wall evaporated, it caused the sporangium to unfurl and eject the spores into the environment.

The researchers examined some fern leaves under a microscope and found that, when exposed to light or heat which caused evaporation, the sporangia opened and released the spores. The methodfor making the material centres on coating a wafer with silicone and hitting it with light, causing a pattern. The residual pattern is lifted off and used for the device.
It resembles a curved spine with equally spaced ribs fanning outwards from the spine. To make the device move, the researchers loaded the space between the ribs with water. When the water evaporates, the surface tension of the water pulls on the tips of the ribs so that the tips move toward each other, straightening out the spine of the device.

Maharbiz plans to add electrical components to the device in an attempt to generate electricity.
The researchers predict that the device will be able to generate the same amount of electricity as other “scavenging” devices, such as a solar cell in a calculator.