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.

"Nanoscale materials are not required for this to work," he said. "Larger fibers work better and are easier to work with to fabricate devices. But the same principle would apply at the nanometer scale."

The wires are grown using a physical vapor deposition method at approximately 600 degrees Celsius. Using an optical microscope, the wires are then bonded onto a polyimide film and silver paste applied at both ends to serve as electrodes. The wires and electrodes were then encased in polyimide to protect them from wear and environmental degradation.

To measure the electric energy generated, the researchers subjected the substrate and attached zinc oxide wires to periodic mechanical bending created by a motor-driven mechanical arm. The bending induced tensile strain which created a piezoelectric potential field along the laterally-packaged wires. That, in turn, drove a flow of electrons into an external circuit, creating the alternating charge and discharge cycle – and corresponding current flow.

Increasing the strain rate increased the magnitude of the output electricity, both in voltage and current. Wang believes the frequency of the current is limited only by the mechanical properties of the polyimide substrate.

The researchers conducted a number of tests to verify that the current measured was produced by the generator – and not an external measurement artifact. Using the same experimental setup, they stretched carbon fibers and Kevlar fibers coated with polycrystalline zinc oxide, and did not observe current flow. The research team also developed two criteria and eight tests for ruling out experimental artifacts, Wang noted.

In addition to Wang, the research team included Rusen Yang and Yong Qin from Georgia Tech and Liming Dai of the Department of Chemical and Materials Engineering at the University of Dayton.

For the future, Wang sees the family of small-scale generators enabling development of a new class self-powered wireless sensing systems. The devices could gather information, store it and transmit the data – all without an external power source.

"Self-powered nanotechnology could be the basis for a new industry," he said. "That's really the only way to build independent systems."

Contact: Zhong Lin Wang (404-894-8008); E-mail: ( )