Wireless Power Transfer via Strongly Coupled Magnetic Resonances

doi:10.1126/science.1143254

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Originally published in Science Express on 7 June 2007
Science 6 July 2007:
Vol. 317. no. 5834, pp. 83 - 86
DOI: 10.1126/science.1143254

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Research Articles

Wireless Power Transfer via Strongly Coupled Magnetic Resonances

André Kurs¹^*, Aristeidis Karalis², Robert Moffatt¹, J. D. Joannopoulos¹, Peter Fisher³ and Marin Solja $c$ i $c$ ¹

¹ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
² Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
³ Department of Physics and Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Fig. 1. Schematic of the experimental setup. A is a single copper loop of radius 25 cm that is part of the driving circuit, which outputs a sine wave with frequency 9.9 MHz. S and D are respectively the source and device coils referred to in the text. B is a loop of wire attached to the load (light bulb). The various ${kappa}$ srepresent direct couplings between the objects indicated by the arrows. The anglebetween coil Dand the loop A is adjusted to ensure that their direct coupling is zero. Coils S and D are aligned coaxially. The direct couplings between B and A and between B and S are negligible. [View Larger Version of this Image (8K GIF file)]

Fig. 2. Comparison of experimental and theoretical values for ${kappa}$ as a function of the separation between coaxially aligned source and device coils (the wireless power transfer distance). [View Larger Version of this Image (17K GIF file)]

Fig. 3. Comparison of experimental and theoretical values for the parameter ${kappa}$ / ${Gamma}$ as a function of the wireless power transfer distance. The theory values are obtained by using the theoretical ${kappa}$ and the experimentally measured ${Gamma}$ . The shaded area represents the spread in the theoretical ${kappa}$ / ${Gamma}$ due to the 5% uncertainty in Q. [View Larger Version of this Image (17K GIF file)]

Fig. 4. Comparison of experimental and theoretical efficiencies as functions of the wireless power transfer distance. The shaded area represents the theoretical prediction for maximum efficiency and is obtained by inserting the theoretical values from Fig. 3 into Eq. 2, with ${Gamma}$ _W/ ${Gamma}$ _D = [1 + ( ${kappa}$ ²/ ${Gamma}$ ²)]^1/2. The black squares are the maximum efficiency obtained from Eq. 2 and the experimental values of ${kappa}$ / ${Gamma}$ from Fig. 3. The red dots present the directly measured efficiency, as described in the text. [View Larger Version of this Image (21K GIF file)]