Wireless electricity spells end for power cables

Posted on 20 Nov 2006 at 09:53

Laptop users may soon be able to abandon their power cables for good after researchers at the Massachusetts Institute of Technology discovered wireless electricity.

Scientists have known that electric power can be transferred wirelessly since 1831, when Michael Faraday discovered that current flowing through one wire induces a current in a neighbouring wire.

Electric motors and power transformers both employ this principle, but only because the two wires are in close proximity. Because the energy from the first wire is transmitted in all directions, it quickly dissipates when the wires are moved apart. To overcome this, the power would have to be cranked up to levels that would zap bystanders with dangerous amounts of electromagnetic radiation.

Marin Soljacic, an assistant professor in MIT's Department of Physics and Research Laboratory of Electronics, realised that by transmitting power via a 'non-radiative' electromagnetic field rather than by electromagnetic waves it would be possible to transfer energy over longer distances, across a room for example, and ensure that only devices specially designed to 'resonate' would be able to receive that energy. Energy not picked up by a receiver would be reabsorbed by the emitter.

Soljacic and his colleagues set about tackling the problem through theoretical calculations and computer simulations.

'It certainly was not clear or obvious to us in the beginning how well it could actually work, given the constraints of available materials, extraneous environmental objects, and so on,' he told MIT's TechTalk.' It was even less clear to us which designs would work best.'

Once the team had working designs they confirmed that non-radiative wireless power would have limited range and that the range would be shorter for smaller-size receivers, mobile phones for example. Nonetheless it calculated that an object the size of a laptop could be recharged within a few metres of the power source; placing one source in each room could provide coverage throughout your home.

Soljacic is looking forward to a future when laptops and cell phones might never need any wires at all, while wireless could also power other household gadgets.

'At home, I have one of those robotic vacuum cleaners that cleans your floors automatically,' he said.'It does a fantastic job but, after it cleans one or two rooms, the battery dies.' But by automatically locating the wireless charger in each room the cleaner could recharge itself as it moves around the house.

Author: Simon Aughton