Wireless energy

US researchers have successfully tested an experimental system to deliver power to devices without the need for wires.

The setup, reported in the journal Science, made a 60W light bulb glow from a distance of 2m (7ft).

WiTricity, as it is called, exploits simple physics and could be adapted to charge other devices such as laptops.

"There is nothing in this that would have prevented them inventing this 10 or even 20 years ago," commented Professor Sir John Pendry of Imperial College London who has seen the experiments. "But I think there is an issue of time. In the last few years we have seen an exponential growth of mobile devices that need power. The power cable is the last wire to be cut in a wireless connection."

The researchers from the Massachusetts Institute of Technology (MIT) who carried out the work outlined a similar theoretical setup in 2006, but this is the first time that it has been shown to work.

The experimental setup consisted of two 60cm (2ft) diameter copper coils, a transmitter attached to a power source and a receiver placed 2m (7ft) away and attached to a light bulb.

With the power switched on at the transmitter, the bulb would light up despite there being no physical connection between the two.

Measurements showed that the setup could transfer energy with 40% efficiency across the gap.

The bulb was even made to glow when obstructions such as wood, metal and electronic devices were placed between the two coils.

"These results are encouraging. The numbers are not far from where you would want for this to be useful," said Professor Soljacic.