Georgia Tech researchers have found a way to power electronic devices with nanoscale generators which draw energy using an array of tiny nanowires directly from the environment.
Zhong Lin Wang, lead author of the paper published in Nano Letters and a Regents' professor in Georgia Tech's School of Material's Science and Engineering, along with his team, have developed nanoscale generators that harvest mechanical energy directly from the environment in an effort to eventually power nanoscale and microscale devices, as well as charge iPods and pacemakers.
The nanogenerators use nanoscale zinc oxide wires to capture an electric charge. To capture an electric charge, the nanogenerators must be compressed or flexed, which can occur from a simply squeezing it between two fingers, or from a heartbeat, the vibration of a machine, the rustling of a shirt or the beat of a shoe on a trail. Researchers found that a nanogenerator can produce up to three volts, and up to 300 nanoamps.
Wang and his team have been working on these nanogenerators for five years, and in that period of time, they have made several improvements to these devices. The earliest versions of zinc oxide nanogenerators were difficult to assemble and required careful growth. These old versions used arrays of nanowires that were grown on a rigid substrate, then a metal electrode was added. Later versions, which consisted of embedding both ends of the nanowires in polymer, then generating power by flexing, required just as careful growth and assembly.
But Wang improved zinc oxide nanogenerators by growing arrays of a brand-new type of nanowire that has a conical shape, and then cut them from their growth substrate and put the wires in an alcohol solution. The alcohol solution was then "dripped" onto a sheet of flexible polymer film as well as a metal electrode. When the alcohol dried, another layer was made and several nanowire/polymer layers were built up into a composite-type structure.
"By simplifying our design, making it more robust and integrating the contributions from many more nanowires, we have successfully boosted the output of our nanogenerator enough to drive devices such as commercial liquid-crystal displays, light-emitting diodes and laser diodes," said Wang. "If we can sustain this rate of improvement, we will reach some true applications in healthcare devices, personal electronics, or environmental monitoring."
Wang has made other improvements in the area of nanogenerators. For instance, in a different paper published last week, Wang developed a new technique for fabricating piezoelectric nanowires from lead zirconate titanate (PZT). He used a process called hydrothermal decomposition at 230 degrees Celsius, and reported the first chemical epitaxial growth of single-crystal, vertically-aligned nanowire arrays of PZT on several non-conductive and conductive substrates. They then used the PZT nanogenerators to power a commercial laser diode with a rectifying circuit, which converted alternating current to direct current. But Wang notes that PZT performance is "not as good as zinc oxide for power generation."
"From when we got started in 2005 until today, we have dramatically improved the output of our nanogenerators," said Wang. "We are within the range of what's needed. If we can drive these small components, I believe we will be able to power small systems in the near future. In the next five years, I hope to see this move into application."
