Thermoacoustic Devices Recycle Excess Heat Into Sound and Energy

Tiny "screaming machines" could stretch battery life in laptops

A U.S. Army-funded research project at the University of Utah has resulted in a crop of unusual devices that turn waste heat into sound energy, then into electricity.

A team led by physics professor Orest Symko is scheduled to demonstrate the thermoacoustic engines Friday at the Acoustical Society of America's annual meeting in Salt Lake City.

One doctoral student participating in the project created a cylindrical device smaller than a penny that can pump out 120 decibels of sound -- roughly equal to that produced by a rock concert or a police siren.

In a statement released by Symko, the researcher said he plans to test a range of thermoacoustic designs developed by the 2-year-old Thermal Acoustic Piezo Energy Conversion (TAPEC) project later this year. The tests will be conducted at an Army radar installation and at the Utah campus' hot water plant.

The Army hopes to harness the technology to reduce waste heat from devices such as radar, and for "producing a portable source of electrical energy which you can use in the battlefield to run electronics,” Symko said.

The TAPEC devices developed so far first convert heat into sound using cylindrical "resonators," which place a sound-producing surface between cold and hot heat exchangers. The resulting pressurized air travels across the surface, producing sound in the same way air pressure across the mouthpiece of a flute creates a musical tone. The sound is then used to drive piezoelectric devices that turn the acoustic pressure into electrical current.

Symko says the noise produced in the process can be mitigated with "sound absorbers." He anticipates that thermoacoustic devices will continue to shrink in size, allowing them to be incorporated in MEMS (microelectromechanical systems) for cooling and powering computers and other electronic devices.