Power transfer system means no more cablesRefrigerators 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.
Even over longer distances, efficiency could be kept at 80 per cent.
As the electromagnetic coupling was not radioactive, there were no health risks even when used throughout an entire house.
The theory has been peer-reviewed and was published in the latest volume of the Institute of Electrical and Electronics Engineers' journal Transactions on Power Electronics last month.
Hui said his team had patented part of the research and the project had been granted about HK$1 million from the government's Innovation and Technology Fund to extend the transmission distance and improve efficiency of the system.
"If it works like it does in theory, we may transmit electricity wirelessly even between continents," he said.