Powered by heat

How about a low-cost and efficient solid-state engine that coverts heat to electricity? Wouldn’t that be lapped up in an energy hungry world? Not only would these engines have no moving parts, they will not wear out, and would be infinitely reliable. They can enable electronic devices that recycle some of their own waste heat into electricity. In a computer, it could enable heat-powered computation, or, inversely, it could provide cooling.

We are not yet there but research is heading there.

Researchers who are studying a new magnetic effect that converts heat to electricity have discovered how to amplify it a thousand times over. Called the spin Seebeck effect, the spin of electrons creates a current in magnetic materials, which is detected as a voltage in an adjacent metal. Ohio State University researchers have figured out how to create a similar effect in a non-magnetic semiconductor while producing more electrical power.

The resulting voltages are admittedly tiny, but in this week's issue of the journal Nature, the researchers report boosting the amount of voltage produced per degree of temperature change inside the semiconductor from a few microvolts to a few millivolts -- a 1,000-fold increase in voltage, producing a 1-million-fold increase in power.

Just as light is made of particles called photons, heat, too, can be thought of the same way, and scientists have a similar-sounding name for heat particles: phonons. The researchers think that they were able to induce a powerful stream of phonons inside the semiconductor. The phonons then smashed into the electrons and knocked them forward, while the atoms in the semiconductor made the electrons spin as they streamed through the material.

There are drawbacks like requiring a low temperature and a high magnetic field as they worked on a non-magnetic material and had to cool surroundings to polarize the electrons. But newer materials may take the discovery further is the hope.