New small-scale generator produces alternating current by stretching zinc oxide wires

Georgia Tech Professor Zhong Lin Wang holds a prototype flexible charge pump. The device generates alternating current as zinc oxide wires are stretched and then released. Click here for more information.

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."

To boost the current produced, arrays of the flexible charge pumps could be constructed and connected in series. Multiple layers of the generators could also be built up, forming modules that could then be embedded into clothing, flags, building decorations, shoes – or even implanted in the body to power blood pressure or other sensors.

When the modules are mechanically stretched and then released, because of the piezoelectric properties, the zinc oxide material generates a piezoelectric potential that alternately builds up and then is released. A Schottky barrier controls the alternating flow of electrons, and the piezoelectric potential is the driving force of the charge pump.

"The electrons flow in and out, just like AC current," Wang explained. "The alternating flow of electrons is the power output process."

Constructed with zinc oxide piezoelectric fine wires with diameters of three to five microns and lengths of 200 to 300 microns, the new generator no longer depends on nanometer-scale structures. The larger size was chosen for easier fabrication, but Wang said the principles could be scaled down to the nanometer scale.