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 centimeters 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.

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