Nanogenerator uses vibrations to charge mobile phone

The so-called nanogenerator - created by engineers at the University of Wisconsin-Madison, the University of Minnesota Duluth, and China’s Sun Yat-sen University - is incorporated directly into the phone’s housing.

‘We believe this development could be a new solution for creating self-charged personal electronics,’ said 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 described their device - a mesoporous piezoelectric nanogenerator - in Advanced Energy Materials.

The nanogenerator takes advantage of polyvinylidene fluoride (PVDF), a common piezoelectric polymer material that can generate electricity from a mechanical force or 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 then etched the nanoparticles off the film, with the resulting interconnected mesopores causing the otherwise stiff material to become sponge-like.

That sponge-like material is key to harvesting vibration energy. ‘The softer the material, the more sensitive it is to small vibrations,’ Wang said in a statement.

The nanogenerator includes thin electrode sheets on the front and back of the mesoporous polymer film, and the researchers can attach this soft, flexible film 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 displacement and amplify 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 vibrations to power the device directly.

Wang said the simplicity of his team’s design and fabrication process could scale well to larger manufacturing settings.

‘We can create tuneable mechanical properties in the film,’ he said. ‘And also important is the design of the device. Because we can realise this structure, phone-powering cases or self-powered sensor systems might become possible.’