Scientists at the University of Utah have developed a way to convert the wasted heat in electronic devices into sound and then electricity, promising cooler, greener, and perhaps louder, computers and other machines.

Orest Symko, the University of Utah physics professor heading the research effort, said in a statement that five of his doctoral students had come up with improved thermoacoustic engines. These devices convert heat into sound waves, which drive a pressure-sensitive mechanism to produce electricity.

The researchers, funded by a U.S. Army effort to improve the performance of battlefield electronics, plan to present their findings this Friday during the annual meeting of the Acoustical Society of America in Salt Lake City, Utah. Scientists from Washington State University and the University of Mississippi also are participating in the project.

One of Symko's doctoral students, Myra Flitcroft, created a cylindrical heat engine about half the size of a penny that generates a 120 decibel whine, which is as loud as a siren or a rock concert.

Student Bonnie McLaughlin designed a one-and-a-half inch by half-inch cylindrical heat engine that's about twice as efficient at converting heat to sound as previous designs. It ran as loud as a jackhammer, about 135 decibels.

"It's an extremely small thermoacoustic device -- one of the smallest built -- and it opens the way for producing them in an array," Symko said.

Symko, however, is confident that Thermal Acoustic Piezo Energy Conversion (TAPEC) won't trade the carbon pollution of wasted electricity for noise pollution. As smaller thermoacoustic engines are developed, he expects that heat will be converted into ultrasonic frequencies beyond human hearing. It's not immediately clear whether such sounds would affect animals.

Symko also said that unwanted sound could be contained with a sound absorber.

The length of the resonator cylinder determines the output tone, with shorter tubes creating higher pitches. Given that one student, Ivan Rodriguez, created a ring-shaped design that proved to be about twice as efficient as cylindrical versions, it also may be possible to mitigate sound issues through resonator design.

Symko expects to test his team's thermoacoustic engines within a year at a military radar site and at the University of Utah's water heating facility.