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New breakthroughs by HKU research team on Wireless Power Transfer Wireless Domino-Resonator Systems for Mid-Range Applications

03 May 2012

A century ago, renowned scientist Nicola Tesla successfully demonstrated that electric power could be transferred wirelessly between a pair of coils called coil-resonators. He laid down the scientific resonance principle that wireless power transfer between a pair of coil-resonators can be achieved with maximum efficiency when the coil-resonators are excited at their "resonance frequency". Wireless power has now found many applications for "short-range" applications such as wireless charging pad for mobile phones. The world first wireless power standard "Qi" is now endorsed by the Wireless Power Consortium (WPC) comprising over 100 companies worldwide.

An HKU research team, led by Professor Ron Hui, Philip K H Wong Wilson K L Wong Professor in Electrical Engineering, and Dr. Chi Kwan Lee, of the Department of Electrical & Electronic Engineering, has recently developed a new wireless power domino-resonator system concept for "mid-range" applications. Mid-range applications refer to wireless power transfer over a distance in the order of magnitude similar to the dimension of the coil-resonators. Unlike the use of a pair of coil-resonators by Tesla, the HKU research team members have successfully demonstrated that electric power can be wirelessly transmitted through several coil-resonators that can be arranged in different "domino" forms, such as straight, circular and Y-shaped dominos. This means that the power flow direction can be controlled and even split into many branches.

Most importantly, they discovered that the maximum efficiency frequency would deviate from the resonance frequency of the coil-resonators, because the cross-coupling of non-adjacent coil-resonators would affect the overall wireless power flow paths. They proved that, while Tesla was correct in stating that the optimal operating frequency is the resonance frequency for a pair of coil-resonators, it will shift away from the resonance frequency if more than 2 coil-resonators are used. In addition, they have developed new techniques to control the power flow in such domino-resonator systems.

The new wireless power domino-resonator systems provide new means of power transfer without using continuous cables over a few metres. This is an emerging technology that enables power to be transmitted in a highly flexible manner. Further research is being conducted by the HKU team to further improve the transmission distance and efficiency under the support of an Innovation & Technology Fund (ITF).

Their new discovery, new theory and practical verification have been peer-reviewed and published in the prestigious IEEE Transactions on Power Electronics in April 2012.

For media enquiries, please contact Ms Trinni Choy (Assistant Director (Media), Communications and Public Affairs Office) tel: 2859 2606, email: pychoy@hku.hk; or Ms Melanie Wan (Manager (Media), Communications and Public Affairs Office) tel: 2859 2600, email: melwkwan@hku.hk.

Professor Ron Hui and Dr. Chi Kwan Lee demonstrate the wireless power transfer system

Wireless domino-resonator systems for mid-range applications