Wireless Power Supplies Using Magnetic Resonance

May 13, 2010 by John Messina, Phys.org weblog
Magnetic induction is the concept used in wireless power supplies.

(PhysOrg.com) -- Until now domestic manufacturers and research institutions have only been focused on the concept that magnetic resonance could be used for wireless power supplies. Companies like Sony Corp. and Toshiba Corp. of Japan have worked out details on extending the range of this technology toward practical applications. University of Tokyo of Japan and Kyoto University of Japan has clearly aimed this technology for practical wireless power supply applications.

In 2007 MIT research team outlined a public experiment (see diagram below) where they used to light up a 60 watt bulb. The coil operated at a frequency of approximately 10 MHz, with a Q factor of 950. The Q factor of a coil is determined by (2πf)L / R, where f= frequency, L =coil inductance and R=coil resistance. A Q factor greater than 1000 is difficult to achieve.

Lighting a 60W Bulb at 2m with Wireless Power Supply. Credit: Nikkei Electronics based on materials courtesy MIT.

A magnetic resonance supply system was discussed in one paper that’s prototyped by the Arakawa & Komurasaki Laboratory of the University of Tokyo together with DENSO Corp. of Japan. Professor Kimiya Komurasaki of the Department of Advanced Energy, Graduate School of Frontier Science at the University, stated: "The system can supply power not only to mobile phones and notebook PCs, but also objects moving freely in free space."

With the prototype system researchers studied the relationship of the resonator’s position within three-dimensional space to transfer efficiency. Both simulated and actual measurements are shown in figure below.

In order to achieve optimal power transfer, impedance matching between coils is a key factor. By changing the distance between the transmitter and receiver causes a change in the coupling constant (K) which causes a change in the optimal impedance ratio.

Transfer Efficiency Affected by Impedance Matching. Credit: Nikkei Electronics based on material courtesy University of Tokyo and DENSO.

The research team aims at boosting transfer efficiency while also including a set of applications that requires less efficiency. For example, a wireless used to power a mobile device would require less efficiency as compared to a large screen TV that requires high efficiency coupling.

Microwave Transmission

Besides magnetic resonance, wireless power supplies can also be designed using microwaves. This method was demonstrated at the Institute of Electronics, Information and Communication Engineers (IEICE) 2010 General Conference held March 16-19, 2010.

Naoki Shinohara, Associate Professor, Research Institute for Sustainable Humanosphere, Kyoto University stated that, "microwave transfer is not at all a low-efficiency technology."

Optimization of antenna positioning can effectively boost efficiency as illustrate in the diagram below. A 12 piece receiving patch mounted in plane was about 60% efficient; whereas an 8-piece receiving patch antenna mounted at an angle, boosted simulated to 83.7%.

Boosting Efficiency with Inclined Receiving Antenna. Credit: Nikkei Electronics based on material courtesy Kyoto University and UD Trucks.

Explore further: Coil in wall could wirelessly power multiple electronic devices

More information: Wireless power transmission system for a Micro Aerial Vehicle - ursi-test.intec.ugent.be/files … 8/papers/HBDGJp7.pdf
Via: Tech-On

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not rated yet May 13, 2010
carbon nanocoils have been shown to work well on batteries, possibly there is an opening in antenna systems?
not rated yet May 14, 2010
Assuming this could be done without being dangerous to medical implants such as pace makers, this would be incredible. Imagine electric vehicles that don't need on-board batteries?
May 14, 2010
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not rated yet May 14, 2010
What biological effects could this have on humans?
Radiation of all sorts are factors in evolution.
Should we not research this area equally to our application of this technology?
not rated yet May 16, 2010
Getting a Q over 100 is hard. You have to stop the energy being absorbed by other items nearby.
not rated yet May 17, 2010
I agree with Au-Pu. I think this has the potential to be more harmful than the puny amounts of microwave radiation coming from our cell phones. And that is something now seen as potentially dangerous. They ask that you use bluetooth so as to keep the phone away from your head. I wonder if keeping it on my belt might do more harm to my children? Not to take anything away, this is an amazing field of study. And; Nikola Tesla imagined a future with this tech in it. We need efficiencies at least equal to A/C along a line before this is doable. Everyone agree there?
not rated yet Jun 05, 2010
Imagine electric vehicles that don't need on-board batteries?

Who's going to lay down all the thousands and thousands of miles of wires under the roads?

And where do you get enough copper?

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