Cell Phones Powered by Conversation?

Sept. 16, 2010— -- Chatty teenagers could be the world's next renewable energy source.

Scientists from Korea have turned the main ingredient of calamine lotion into a tiny material that converts sound waves into electricity. The research could lead to panels that can charge a cell phone from a conversation or provide a boost of energy to the nation's electrical grid generated by the noise during rush hour traffic.

"Just as speakers transform electric signals into sound, the opposite process -- of turning sound into a source of electrical power -- is possible," said Young Jun Park and Sang-Woo Kim, the two corresponding authors of a new article in the journal Advanced Materials.

"Sound power can be used for various novel applications including mobile phones that can be charged during conversations and sound-insulating walls near highways that generate electricity from the sound of passing vehicles," the co-authors added.

Harvesting energy from phone calls and passing cars is based on materials known as piezoelectrics. When bent, a piezoelectric material turns that mechanical energy into electricity.

Lots of materials are piezoelectric: cane sugar, quartz and even dried bone creates an electrical charge when stressed. For decades, scientists have pumped electricity into piezoelectric materials for use in environmental sensors, speakers and other devices.

Over the last few years, however, scientists have made dramatic advances in getting electricity out of piezoelectric devices. Most of these devices, which are not yet available for consumer purchase, would generate power as a person walks, runs or, in this case, talks. The U.S. Army is even looking at partially powering some vehicles by channeling the physical impact of a bullet into a small electrical current.

The Korean scientists, however, want to harness a different kind of power source: sound waves.

Using zinc oxide, the main ingredient in calamine lotion, Young Jun Park, Sang-Woo Kim and their colleagues created a field of nanowires sandwiched between two electrodes. The researchers blasted that sandwich with sound waves, which at 100 decibels were not quite as loud as a rock concert. A normal conversation is about 60-70 decibels.