Putting waste heat from electronics to good use
By Ben Coxworth
September 28, 2010
Researchers at two different institutions have recently announced the development of technologies for converting waste heat from electronics into something useful. At the California Institute of Technology (Caltech), they’ve created a silicon nanomesh film that could collect heat from electric appliances such as computers or refrigerators and convert it to electricity. Meanwhile, their colleagues at Ohio State University (OSU) have been working with a semiconducting material that has the capacity to turn waste heat from computers into additional processing power.
The Caltech scientists claim that their material is much more efficient and/or inexpensive and environmentally-friendly than other thermoelectric solutions that have been proposed to date. It takes the form of a 22-nanometer-thick sheet of silicon, containing a window screen-like matrix of 11- or 16-nanometer-wide holes that are spaced 34 nanometers apart.
The design significantly lowers the film’s thermal conductivity, meaning heat can’t easily travel through it and escape. At the same time, however, electricity can still travel through it well. Lowered thermal conductivity combined with decent electrical conductivity has always been one of the goals of designers of thermoelectric devices.
Heat travels via packets of vibration known as phonons, and the nanomesh slows those phonons down, so their energy can be harvested before it chaotically disperses throughout the material. The researchers are now experimenting with different arrangements of holes, and different materials.
For some time now, researchers around the world have been trying to develop electronics that utilize spinning electrons to read and write data – a concept known as spintronics. Unlike traditional circuits, spintronics would supposedly not create any heat. At OSU, scientists have been experimenting with using a semiconducting material to convert heat into electron-spinning energy. This means, theoretically, that the heat generated by a computer could be used to provide more processing power or memory for that same computer.
In 2008, researchers at Japan’s Tohoku University showed how heat could be converted into spin polarization. The not-entirely-understood phenomenon is known as the spin-Seebeck effect. In this case, researchers just used a piece of metal.
The OSU researchers have duplicated the results from Japan, but using semiconducting gallium manganese arsenide, which would be better-suited for use in computers.
Such a “thermo-spintronic” approach would simultaneously address two challenges facing computer designers, namely waste heat removal, and the difficulty in obtaining more computing power without creating more heat.
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