New device charges your cell phone while you walk

Scientists have developed a new device that can generate electricity from your body movements to power your cell phone. The device built by researchers from the Georgia Institute of Technology consists of four discs layered on top of one another.

The first disc is made of copper, and rotates. The next is a polymer and remains stationary, and the third is a gold layer that is divided into sectors, with alternating sections cut out, to make something that looks like a bicycle wheel. The last layer is made of acrylic.

When the copper disc rotates, positive charges in the copper move past the negative charges in the polymer. This causes an imbalance of charges in the gold layer, with each "spoke" of gold having either more positive or more negative charges.

The imbalance means that when a wire is connected between sectors, a current flows.

The team led by researcher Zhong Lin Wang said the device can generate power as long as something causes the copper disc to rotate.

The device works on the same principle as static electricity. For example, when you walk on a rug in wool socks, electrons build up in the socks (and in you), and when you touch a metal doorknob, they jump from your finger, making a spark, 'LiveScience' reported.

Wang said the new device is more efficient than a traditional generator, at least for its size.

A generator works by moving either a wire through a magnetic field or a magnetic field over a stationary wire. Either one requires a certain number of turns of wire to make a certain voltage, plus a strong magnet.

However, the device the researchers created can be made thin and flat. The prototype demonstrated by Wang was about 10 centimetres across, and swinging it in the hand generated enough electricity to power a small array of lights, or about 5 volts, which is enough to charge an iPhone.

Wang said the device is 50 times more efficient than a traditional generator of the same size.

The details of the device are published in the journal Nature Communications.