Could nanotech create speech-powered phones?

A variety of off-grid devices use the wind, the sun, or fuel cells to power up small electronics. But what if you could charge your cell phone just by talking into it, eliminating the need for batteries or cords?

What would make this possible is piezoelectricity, in which a mechanical force is converted to electricity. Some cigarette and barbeque grill lighters are an example. When a button is punched, pressure on a crystal within produces voltage, creating a spark.

In principle, the pressure to power a device could come from sound vibrations.

Crafting such piezoelectric electronics would require sensors with a specific size of crystal or ceramic material. Engineers say they have taken an early step by identifying a sweet spot at which a crystal could produce energy.

The capability of barium titanate crystals to harvest power doubles when they're about 23 nanometers in size, according to an analysis led by engineer Tahir Cagin at Texas A&M University. A human hair, for contrast, is about 100,000 nanometers wide.

However, it could be years or decades before scientists and entrepreneurs apply the findings to consumer products, he said.

"There are limitations to how much power you can generate at a given size," said Cagin, adding that an iPod or cell phone may require nano-sensors at a scale and composition different from what his research suggested.

For now, at least, wind-up radios, shake flashlights, and other devices that use kinetic energy for power are currently available. Products under development include a dance-powered iPod charger that could be worn on an arm. M2E Power is building motion-powered gadget chargers that could come to market in 2009.

At a larger scale, people are increasingly using piezoelectricity for off-grid, "green" power. Dancing feet produce electricity at nightclubs in London and the Netherlands, and a San Francisco nightclub could follow suit. A gym in Portland, Ore., has rigged some exercise equipment to generate 750 watts.

The journal Physical Review B this fall published Cagin's research, in which engineers at the University of Houston also participated.