A multi-university team of engineers has developed what could be a promising¹ solution for charging smartphone batteries on the go -- without the need for an electrical cord. Incorporated（合并，包含） directly into a cell phone housing, the team's nanogenerator could harvest and convert vibration² 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," says Xudong Wang, an assistant professor of materials science and engineering at the University of Wisconsin-Madison.

 

Wang, his Ph.D. student Yanchao Mao and collaborators from Sun Yat-sen University in China, and the University of Minnesota Duluth described their device, a mesoporous（介孔） piezoelectric（压电的） nanogenerator, in the January 27, 2014, issue of the journal Advanced Energy Materials.

 

The nanogenerator takes advantage of a common piezoelectric polymer material called polyvinylidene fluoride（聚偏二氟乙烯）, or PVDF. Piezoelectric materials can generate electricity from a mechanical force; conversely, they also can generate a mechanical strain from an applied³ electrical field.

 

Rather than relying on a strain or an electrical field, the researchers incorporated zinc⁴ oxide⁵ nanoparticles into a PVDF thin film to trigger formation of the piezoelectric phase that enables it to harvest vibration energy. Then, they etched the nanoparticles off the film; the resulting interconnected pores -- called "mesopores" because of their size -- cause 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 vibrations⁶," says Wang.

 

The nanogenerator itself includes thin electrode sheets on the front and back of the mesoporous polymer film, and the researchers can attach this soft, flexible film seamlessly to flat, rough or curvy surfaces, including human skin. In the case of a cell phone, it uses the phone's own weight to enhance its displacement⁷ and amplify⁸ its electrical output.

 

The nanogenerator could become an integrated part of an electronic device -- for example, as its back panel or housing -- and automatically harvest energy from ambient（周围的） vibrations to power the device directly.

 

Wang says the simplicity⁹ of his team's design and fabrication process could scale well to larger manufacturing settings. "We can create tunable¹⁰ mechanical properties in the film," he says. "And also important is the design of the device. Because we can realize this structure, phone-powering cases or self-powered sensor¹¹ systems might become possible."

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