University of Utah physicists have developed small devices that turn heat into sound and then into electricity. The technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars.

“We are converting waste heat to electricity in an efficient, simple way by using sound,” said Orest Symko, a University of Utah physics professor who leads the project. “It is a new source of renewable energy from waste heat.”

Five of Symko’s doctoral students recently devised methods to improve the efficiency of acoustic heat-engine devices to turn heat into electricity. They presented their findings in June during the annual meeting of the Acoustical Society of America.

Funded by the U.S. Army, Symko plans to test the devices within a year to produce electricity from waste heat at a military radar facility and at the university’s hot-water-generating plant.

Most of the heat-to-electricity acoustic devices built in Symko’s laboratory are housed in cylinder-shaped “resonators” that fit in the palm of a hand. Each resonator contains a stack of material with a large surface area—such as metal or plastic plates, or fibers made of glass—placed between a cold heat exchanger and a hot heat exchanger.

When heat is applied, it builds to a threshold, then the hot, moving air produces sound at a single frequency, similar to air blown into a flute. Then the sound waves squeeze a piezoelectric device, which respond to pressure, producing an electrical voltage. According to Symco, it’s similar to what happens if you hit a nerve in your elbow, producing a painful electrical nerve impulse.

Symko expects the devices could be used within two years as an alternative to photovoltaic cells for converting sunlight into electricity. The heat engines also could be used to cool laptop and other computers that generate more heat as their electronics grow more complex. In addition, Symko foresees using the devices to generate electricity from heat that now is released from nuclear power plant cooling towers. EC