February 14, 2010

MIT improves Wireless Power Transfer

MIT researchers have developed a system that can wirelessly transfer power to multiple electronic devices simultaneously with high efficiency (over 50%). 25 watts of power was supplied to each of two electronic devices located two meters or more from the source coil

(3 page pdf) Simultaneous mid-range power transfer to multiple devices

The approach of having one large source power multiple small devices distributed over a large volume may therefore lead to good overall efficiencies e.g., greater than 50% even in cases where the single device efficiencies are modest e.g., worse than 20%.

In conclusion, we have derived analytically and shown experimentally for the case of two devices the effect on the overall efficiency and on the loading of the devices of adding multiple device resonators to a system of strongly coupled resonant modes. We find that the approach of powering multiple devices simultaneously can result in a good overall efficiency
for the wireless power transfer even if the efficiency of the transfer to each individual device is relatively low.

Wireless Power Safety and Power up to 3000 Watts so Far

Magnetism from MRI machines can disable pacemakers. Wouldn't wireless electricity pose similar risks? Soljacic replied that MRI magnetism is about 10,000 times stronger than his version. The Institute of Physics in London concurs: so far as it is aware, and based on current medical evidence, WiTricity's magnetic field "has no detrimental effects on the human body

Giler makes a point of standing between the coils whenever he demonstrates the technology. At the Nikkei electronics conference in Tokyo in October, he was able to power a 1,000-watt klieg light from across the room -- a far cry from that 60-watt lightbulb in Soljacic's first experiment. "We're going up the power curve," he says.

WiTricity's record so far is 3,000 watts -- enough to fully charge an electric car, so long as it's in the same room (or garage). How big could WiTricity get? "Every single person in the world can relate to the problem of running out of batteries or having wires everywhere," Giler says. "The market is so potentially huge that numbers become meaningless."

Applied Physics Letters - Simultaneous mid-range power transfer to multiple devices

Electromagnetic resonators strongly coupled through their near-fields [A. Karalis, J. D. Joannopoulos, and M. Soljačić, Ann. Phys. 323, 34 (2008); A. Kurs, A. Karalis, R. Moffatt, J. D. Joannopoulos, P. Fisher, and M. Soljačić, Science 317, 83 (2007)] are able to achieve efficient wireless power transfer from a source to a device separated by distances multiple times larger than the characteristic sizes of the resonators. This midrange approach is therefore suitable for remotely powering several devices from a single source. We explore the effect of adding multiple devices on the tuning and overall efficiency of the power transfer, and demonstrate this scheme experimentally for the case of coupling objects of different sizes: a large source (1 m2 in area) powering two smaller devices (each 0.07 m2 in area).


Soljacic papers

Efficient wireless non-radiative mid-range
energy transfer (15 page pdf 2007)

Witricity is a company formed by the MIT researchers to commercialize wireless power

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