Researchers have developed a new type of small-scale electric power generator able to produce alternating current through the cyclical stretching and releasing of zinc oxide wires encapsulated in a flexible plastic substrate with two bonded ends.

The new flexible charge pump generator is the fourth generation of devices designed to produce electrical current by using the piezoelectric properties of zinc oxide structures to harvest mechanical energy from the environment. Its development was reported November 9, 2008 in the advance online publication of the journal Nature Nanotechnology.

"The flexible charge pump offers yet another option for converting mechanical energy into electrical energy," said Zhong Lin Wang, Regent's professor in the School of Materials Science and Engineering and director of the Center for Nanostructure Characterization at the Georgia Institute of Technology. "This adds to our family of very-small-scale generators able to power devices used in medical sensing, environmental monitoring, defense technology and personal electronics."

The new generator can produce an oscillating output voltage of up to 45 millivolts, converting nearly seven percent of the mechanical energy applied directly to the zinc oxide wires into electricity. The research has been supported by the U.S. Department of Energy, the National Science Foundation, the Air Force Office of Scientific Research and the Emory-Georgia Tech Center for Cancer Nanotechnology Excellence.

Figure 1. The Illustration (top) shows how the flexible charge pump works, while the micrograph shows an actual prototype. Source: Georgia Institute of Technology.

Earlier nanowire nanogenerators and microfiber nanogenerators developed by Wang and his research team depended on intermittent contact between vertically-grown zinc oxide nanowires and an electrode, or the mechanical scrubbing of nanowire-covered fibers. These devices were difficult to construct, and the mechanical contact required caused wear that limited how long they could operate. And because zinc oxide is soluble in water, they had to be protected from moisture.

"Our new flexible charge pump resolves several key issues with our previous generators," Wang said. "The new design would be more robust, eliminating the problem of moisture infiltration and the wearing of the structures. From a practical standpoint, this would be a major advantage."