Wireless Electricity

Recharging your laptop computer, your cell phone and a variety of other gadgets may one day be as convenient as surfing the web--wirelessly.

Recently, a team from the Massacussetts Institute of Technology made a 60-watt lightbulb glow using electricity sent wirelessly between copper coils set seven feet apart.

Scientists have known for years that electricity can be transferred without wires, but had struggled to find a practical and efficient way of making it work.

Professor Marin Soljacic used the concept of resonance. Energy can be efficiently transferred between objects that resonate at the same frequency, so he used two copper coils, one transmitting and the other receiving power.

Professor Soljacic said: "We have promising ideas as to how to achieve this, so now is a good time to start seriously thinking about commercialisation."

However, up to 45 per cent of the transmitted power was lost before it reached the lightbulb, and Professor Soljacic said the system needed to be twice as efficient before it would be as effective as chemical batteries. Also the copper transmitting coils were two feet high, although there was potential for miniaturising them.

He said the project was inspired by his annoyance at being woken up by his mobile phone beeping when he had forgotten to recharge it.

How wireless power could work

1) Power from mains to antenna, which is made of copper
2) Antenna resonates at a frequency of 6.4MHz, emitting electromagnetic waves
3) 'Tails' of energy from antenna 'tunnel' up to 5m (16.4ft)
4) Electricity picked up by laptop's antenna, which must also be resonating at 6.4MHz. Energy used to re-charge device
5) Energy not transferred to laptop re-absorbed by source antenna. People/other objects not affected as not resonating at 6.4MHz

news from BBC News, The Independent, MIT