Cell phones can be charged using sound

Soon you can use traffic noise, music, chants from a football ground and even your own voice to charge your cell phone!
Scientists from Queen Mary University of London and Nokia have created an energy-harvesting prototype (a nanogenerator) that could be used to charge a cell phone using everyday background noise - such as traffic, music, and our own voices.
The team used the key properties of zinc oxide, a material that when squashed or stretched creates a voltage by converting energy from motion into electrical energy, in the form of nanorods.
The nanorods can be coated onto various surfaces in different locations making the energy harvesting quite versatile. When this surface is squashed or stretched, the nanorods then generate a high voltage.

The nanorods respond to vibration and movement created by everyday sound, such as our voices. Electrical contacts on both sides of the rods are then used to harvest the voltage to charge a phone, 'phys.Org' reported.
Researchers first developed a process whereby they could spray on the nanorod chemicals - almost like nanorod graffiti - to cover a plastic sheet in a layer of zinc oxide.

When put into a mixture of chemicals and heated to just 90 degrees C, the nanorods grew all over the surface of the sheet.
Secondly, gold is traditionally used as an electrical contact but the team were able to produce a method of using cheap and cheerful aluminium foil instead.

The ultimate device generates five volts, which is enough to charge a phone.
"Being able to keep mobile devices working for longer, or do away with batteries completely by tapping into the stray energy that is all around us is an exciting concept," said Dr Joe Briscoe from QMUL's School of Engineering and Materials Science.