Piezo device harvests energy from sound

Researchers in London have developed a device that uses sound to help generate an electrical charge, a development that could see mobile phones recharged by everyday background noise.

The device from Queen Mary University of London (QMUL) uses the piezoelectric properties of zinc oxide (ZnO) nanorods to harvest energy from vibration and movement.

To make the device, ZnO nanoparticles are sprayed onto a plastic surface, which is then placed into a solution containing hexamethylenetetramine (HMT) and heated to 90oC. The hexagonal nanorods then grow from that layer of ZnO particles to cover the whole surface.

The team then used aluminium foil to form the electrical contacts. Furthermore, the coating can be applied to a range of surfaces.

According to QMUL, the ultimate device was the same size as a Nokia Lumia 925 and generated five volts.

Dr Joe Briscoe, a post doctoral research assistant at QMUL explained that decibel levels of around 70dB and above will give a measurable response, but more work remains to be done in order to increase the amount of power the device can generate. The team will also refine the methods used to produce the devices.

Dr Briscoe added that vibrations have even more potential than sound to charge a battery.

He said via email: ‘A direct vibration such as in a vehicle or from machinery should be able to excite the piezoelectric material a lot more, and so generate more power.

‘This would work by, for example, building the device into a phone so that if you put it on a table on a train, or maybe even in your pocket, or on the dashboard of the car, the device would vibrate, and convert this vibration into electricity.

‘A final device could be incorporated into a phone in a couple of ways – you could have a small sheet…which you had in your bag or your wallet, which stored some charge from the vibration, and you then plugged it into your phone to top it up. Or you could coat part of the phone case with the piezoelectric material  – which in itself is very very thin – and then the phone would always charge a little when it picked up enough sound or vibration.’

QMUL worked with Microsoft to develop the proof-of-concept nanogenerator.