Today's portable electronics (except for self-winding watches and crank radios) depend on batteries for power. Now researchers have demonstrated that easy-to-make, inexpensive nanowires can harvest mechanical energy, possibly leading to such advances as medical implants that run on electricity generated from pulsing blood vessels and cell phones powered by nanowires in the soles of shoes.
"When you walk, you generate 67 watts. Your finger movement is 0.1 watt. Your breathing is one watt. If you can convert a fraction of that, you can power a device. From the concept we've demonstrated, we can convert 17-30 percent of that," says Zhong Lin Wang, professor of materials science at Georgia Tech and one of the researchers of the work, published in the journal Science.
Their results confirm a theory: zinc oxide nanowires will show a powerful piezoelectric effect, which is the production of electricity in response to mechanical pressure. Ordinarily the positive and negative charges of zinc and oxygen ions in these crystalline nanowires cancel each other out. But when the wires, which are chemically grown to stand on end on top of an electrode, bend in response to, say, a vibration, the ions are displaced. This unbalances the charges and creates an electric field that produces a current when the nanowire is connected to a circuit.