Mobile phone manufacturer Nokia is trying out a new technique for charging up its Lumia smartphones: harvesting the energy produced by everyday background noise to recharge the battery.
Battery charging is today a key area of concern for electronic hardware manufacturers, especially the makers of smartphones. Most of these devices use lithium rechargeable batteries, which nevertheless have a number of disadvantages. First and foremost, these radioactive batteries have to be shielded by solid material to avoid causing harm, which places serious constraints on hardware design. In addition, they cannot be recharged indefinitely. Today there are a number of research projects look into alternatives to lithium for use in batteries, such as the flexible batteries being developed by California-based startup Imprint Energy. Nokia however has been pursuing a revolutionary approach: harvesting electrical energy from sound waves generated by everyday ambient noise. The whole process depends entirely on the use of nanotechnologies.
Novel properties at nano-scale
In order to develop the technique of harvesting energy from sound waves, the Nokia teams got together with two nanotechnology specialists, Dr Joe Briscoe and Dr Steve Dunn of Queen Mary University of London (QMUL), to develop a nanogenerator, which converts mechanical energy into electrical energy. It has been observed that at nano-scale – a nanometre equals a billionth of a metre – certain materials behave in novel ways. They may for instance change colour, become more solid, or become more chemically reactive. This last property is demonstrated by zinc oxide, the main component of the prototype’s nanogenerator which, when shaped into nanorods, can be used to transform vibrations into electrical energy. The nanorods can be spray-coated on to various surfaces in different locations, creating a highly-versatile energy harvesting mechanism. Now that the researchers have found a way to transform sound into electrical energy, it should be feasible to draw on music, traffic noise, crowd chants at a football ground or even your own voice to charge up your mobile phone.
Sound waves as power source
Basically, zinc oxide has what are known as piezo-electrical properties, i.e. when mechanical stress, such as squeezing, is applied to the material, an electrical charge accumulates. An example of this process in action is a cigarette lighter. When you press the button on the lighter, the pressure applied to the piezo-electrical component creates electrical energy – the spark – which ignites the gas. Produced in the form of nanorods, zinc oxide can be coated on to almost any surface. To do this, the QMUL team developed a way of spraying on the nanorod chemicals – like a sort of ‘nanorod graffiti’ – to cover a plastic sheet. When immersed in a mixture of chemicals and heated to just 90°C, the zinc oxide nanorods grew all over the surface of the sheet. While gold is traditionally used as an electrical conductor, the Nokia/QMUL team was able to invent a method that uses much cheaper aluminium foil instead. By picking up the vibrations and movement created by everyday sound, the nanorods can generate 5 volts, sufficient power to charge up a Nokia Lumia 925. So sound waves have the potential to provide an alternative source of energy and experiments are now going on which, if successful, will see sound waves helping to power tomorrow’s world of the Internet of Things.