Refrigerators with no power cords and mobile phones that can be charged though a wall are on the way thanks to a wireless power transfer system developed by University of Hong Kong researchers.
Wireless transfer based on electrodynamic induction - where electricity passes from one device to another without any direct connection as in a rechargeable electric toothbrush - has been around for years. But until now it was possible only over short distances.
The system devised by Ron Hui Shu-yuen, chair professor of power electronics at the university, and Lee Chi-kwan, assistant professor of electrical and electronic engineering, can transmit power over what they term a medium range of a few metres.
The electricity travels through an electromagnetic coupling between a series of resonating coils arranged in domino-like patterns that allow flow to be reversed or even split into branches with little power loss.
'With the multiple coils system, electricity passes through distance as in a relay [race],' Hui said. 'We can easily charge a mobile phone or supply power to the television next door through the wall.'
When the system was patented by Serbian-American inventor Nikola Tesla more than a century ago, it was assumed it would work only between two coils, limiting the distance over which it could be used. But the team found a way of making the power travel from coil to coil. Hui - who also invented the first universal wireless battery charging plate for hand-held electronic products in 2005 - said the new system would be useful in sites such as heritage buildings where drilling was not allowed.