A multi-university team of engineers has incorporated directly into a cell phone housing a nanogenerator that could harvest and convert vibration energy from a surface, such as the passenger seat of a moving vehicle, into power for the phone.
"We believe this development could be a new solution for creating self-charged personal electronics," said Xudong Wang, assistant professor of materials science and engineering at the University of Wisconsin-Madison.
The nanogenerator takes advantage of a common piezoelectric polymer material called polyvinylidene fluoride, or PVDF. Piezoelectric materials can generate electricity from a mechanical force; conversely, they also can generate a mechanical strain from an applied electrical field.
Rather than relying on a strain or an electrical field, the researchers incorporated zinc oxide nanoparticles into a PVDF thin film to trigger formation of the piezoelectric phase that enables it to harvest vibration energy. They etched the nanoparticles off the film, resulting in interconnected mesopores, causing the otherwise stiff material to behave somewhat like a sponge.
That sponge-like material is key to harvesting vibration energy. "The softer the material, the more sensitive it is to small vibrations," said Wang.
The nanogenerator itself includes thin electrode sheets on the front and back of the mesoporous polymer film. The researchers can attach the soft, flexible film seamlessly to flat, rough or curvy surfaces, including human skin. They used the phone's own weight to enhance its displacement and amplify its electrical output.
The nanogenerator could be used as an integrated part of an electronic device and automatically harvest energy from ambient vibrations to power the device directly.
"We can create tunable mechanical properties in the film, and because we can realize this structure, phone-powering cases or self-powered sensor systems might become possible," said Wang.
Wang collaborated with researchers from Sun Yat-sen University in China and the University of Minnesota Duluth. They describe their device in the Jan. 27, issue of the journal Advanced Energy Materials.
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