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Energy-Harvesting Tech Could Boost Power for Cell Yellers

Energy-Harvesting Tech Could Boost Power for Cell Yellers

Cellphone users in coming years may be able to charge their devices simply by speaking into them, if research like that of South Korea's Sang-Woo Kim comes to fruition. The Sungkyunkwan University scientist is making advances in energy-harvesting techniques for turning sound into small amounts of energy that could be used to power highly efficient mobile devices.

By Richard Adhikari
05/09/11 11:47 AM PT

The phrase "In the beginning was the Word" may soon take on a whole new meaning for cellphone users, if work being done by a researcher at South Korea's Sungkyunkwan University pans out.

The scientist, Sang-Woo Kim, has been working on converting sound into electricity.

Among other things, the technology might harness cellphone users' voices to charge their devices' batteries while they're talking, Woo has speculated.

A prototype device he used generated 50 millivolts of electricity from about 100 decibels of sound, The Telegraph reported.

About Woo's Device

Woo's device reportedly uses tiny strands of zinc oxide placed between two electrodes, capped off with a sound-absorbing pad on top. The pad vibrates when it's hit by sound waves, compressing the zinc oxide strands. The strands then decompress, much like springs will when you press down on them.

It's that movement that generates an electrical current.

Apparently, 100 decibels of sound generated 50 millivolts of electricity. One millivolt is a thousandth of a volt.

Loud passages in classical symphonies exceed 100 decibels, while rock concerts "easily exceed" 130 decibels, Orest Symko, a physics professor at the University of Utah, told TechNewsWorld.

Why zinc oxide? It's a wide-band gap semiconductor.

Semiconductors have smaller band gaps than insulators. They conduct electricity at room temperature.

A band gap, also called an "energy gap," is an energy range in a solid where no electron states can exist. It generally refers to the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.

Powering Up With Sound

"Turning sound into electricity isn't anything new," Carl Howe, director of anywhere consumer research at the Yankee Group, told TechNewsWorld. "Piezoelectric devices have existed for decades. It is the principle used for the microphone built into most cellphones."

The University of Utah's Symko has been working on a variant on the conversion of sound to power since 2005. That year, he kicked off a five-year project to convert heat to sound and then to electricity, with collaborators at Washington State University and the University of Mississippi.

The project, named "Thermal Acoustic Piezo Energy Conversion" (TAPEC), uses heat engines developed by the researchers to convert heat into sound. The sound is beamed at piezoelectric devices to convert it into electricity.

Piezoelectric devices compress in reaction to pressure, including sound waves, and change that pressure into electrical current.

"We're interested in using waste heat from power plants, nuclear power plants, computers and automobiles and converting that into electricity," Symko said.

TAPEC was initially funded by the U.S. Army. The project is continuing, and Symko is looking to source more funds to keep it going.

Let's Make Some Noise!

"While the energy currently generated by Dr. Woo's experiment isn't enough to charge a battery today, it sounds like he's optimistic enough about the approach to think it might do so in the future," the Yankee Group's Howe said.

This technology falls into the broad category of energy harvesting, or getting power from everyday activities, Howe pointed out. The self-winding watch is an early example of an energy harvesting device, collecting and storing kinetic energy generated by its wearer's moment, he said.

"What's changed now is that we can use nanotechnology -- very small mechanical structures -- to power nanoelectronics, which require less and less power to operate," Howe stated.

"The hope is that, just like self-winding watches, at some point we won't have to consciously spend our time recharging our devices, they'll just be powered by our routine activities," he added.

Harvesting energy from sound could be combined with other solutions such as kinetic energy harvesting and solar panels, suggested Jim McGregor, chief technology strategist at In-Stat.

"That might be enough to recharge a handset or power a plethora of other low-power devices," McGregor told TechNewsWorld.

"I think mobile devices or low-power devices would be the obvious focus," McGregor added.


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