Rock music could soon charge your phone

A new device harvests energy from noise. James Urquhart reports.

The nanogenerators generate five volts from blasts of rock music – the highest voltage yet achieved using just sound. – iStock

The dilemma of charging your phone at rock festivals could soon be over, thanks to a new device that harvests energy from noise.

The prototype “nanogenerator”, developed by Joe Briscoe, Steve Dunn and their colleagues at Queen Mary University of London in collaboration with Nokia, is able to generate five volts – the minimum required to charge a phone via a USB cable – from blasts of rock music. That is the highest voltage yet achieved using just sound.

The wafer-thin nanogenerator is like an electronic sandwich. Two layers of conductive aluminium foil enclose a plastic sheet that is coated with billions of zinc oxide nanorods. The nanorods bristle from the plastic like the hairs of the inner ear. And just like them the nanorods wobble in response to sound vibrations. Since zinc oxide is piezoelectric, the wobbles create electrical charge that can be captured by the foil and funnelled to the phone’s battery.

The team tested the prototype by playing various types of music and measuring the voltage and current. “Anything that creates a lot of vibration is better. So rock music with a lot of loud, heavy portions is best,” Briscoe explains.

The next step for the team will be to slightly increase the current, which so far falls just short of what is needed to charge phones at this voltage.

Briscoe and Dunn’s work with Nokia builds on their previous research, published in Advanced Materials last November, testing the effect of noise on zinc oxide-based thin-film solar cells. When subjected to rock music or ambient noise from traffic or crowds they saw a boost in performance of the cells’ sunlight-to-electricity conversion efficiency of up to 50%. “We used the same zinc oxide nanorods in our latest work as in the solar cells. But this time we used them to directly produce power from sound rather than boost a solar cell,” explains Briscoe.

Other groups have attempted to create phone chargers using similar concepts, but Briscoe says their devices have struggled with very high electrical resistance. This makes it difficult to extract power and transfer it to the battery. “Ours is based on a different design and the fabrication techniques are quite different as well,” says Briscoe.

Joe Briscoe from Queen Mary University of London tests the nanogenerator that harvests sound energy. – Microsoft

The way the team made their nanogenerators in the lab should be relatively cheap and simple to replicate on a larger scale. One new technique they have developed allows them to seed the growth of nanorods by spraying an initial zinc oxide layer on almost any surface. And rather than having to use expensive gold foil electrodes to collect electric charge the team developed a way to use cheap aluminium foil instead.

“This made it very easy to make devices which were almost as large as you want without using expensive equipment or materials,” Briscoe says.

The new nanogenerators, shown to the right of the smartphones they charge, use cheap aluminium foil electrodes instead of expensive gold. – Microsoft

As well as promising extended battery life for mobile phones the development boosts the possibility of other devices, like medical implants and hearing aids, being powered by sound. Briscoe is hopeful that further work can achieve the power levels required.

And a nanogenerator would not have to be a phone’s sole power source, says Paul Weaver, who investigates energy-harvesting materials at UK's National Physical Laboratory. “To be effective, it does not have to completely replace the battery – simply extending battery life by harvesting energy would be worthwhile.”

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