A capacitor-loaded coupled loop structure is investigated for wireless power transfer at 6.78 MHz for a target transmission distance of 1 m. It is shown that the optimal configuration for this structure occurs when the coupled loops are coplanar. Therefore, by converting thick wires into wide strips, a planarized configuration can be achieved. Simulation results are verified in measurement, which shows a 60% overall power transfer efficiency at 1 m. The contribution of different loss mechanisms is examined. Next, power transfer efficiency in the presence of dielectric materials is investigated in simulation and measurement. Additionally, tuning capabilities that arise from the implementation of variable capacitors are shown. Finally, design space exploration is performed to examine design tradeoffs.
2. Karalis, A., J. D. Joannopoulos, and M. Soljacic, "Efficient wireless non-radiative mid-range energy transfer," Ann. of Phys., Vol. 323, No. 1, 34-48, January 2008.
3. Balanis, C. A., Antenna Theory: Analysis and Design, 2nd Edition, Sec. 8.5, Wiley, New York, 1997.
4. Yoon, I.-J. and H. Ling, "Realizing efficient wireless power transfer using small folded cylindrical helix dipoles," IEEE Antennas Wireless Propag. Lett., Vol. 9, 846-849, September 2010.
5. Pozar, D. M., Microwave Engineering, 3rd Edition, Wiley, New Jersey, 2004.
6. Lee, J. and S. Nam, "Fundamental aspects of near-field coupling small antennas for wireless power transfer," IEEE Trans. Antennas Propagat., Vol. 58, No. 11, 3442-3449, November 2010.
7. Sample, A. P., D. A. Meyer, and J. R. Smith, "Analysis, experimental results, and range adaptation of magnetically coupled resonators for wireless power transfer," IEEE Trans. Ind. Electron., Vol. 58, No. 2, 544-554, February 2011.
8. Klein, A. and N. Katz, "Strong coupling optimization with planar resonators," Curr. Appl. Phys., Vol. 11, No. 5, 1188-1191, February 2011.
9. Park, J., Y. Tak, Y. Kim, Y. Kim, and S. Nam, "Investigation of adaptive matching methods for near-field wireless power transfer," IEEE Trans. Antennas Propag., Vol. 59, No. 5, 1769-1773, May 2011.
10. Kim, H. and H. Lee, Design of an integrated wireless power transfer system with high power transfer efficiency and compact structure, Proc. EuCAP, 3627-3630, Prague, Czech Republic, March 2012.
11. Xue, R.-F., K.-W. Cheng, and M. Je, "High-efficiency wireless power transfer for biomedical implants by optimal resonant load transformation," IEEE Trans. Circuits Syst. I, Vol. 60, No. 4, 867-874, April 2013.
12. Jonah, O., A. Merwaday, S. V. Georgakopoulos, and M. M. Tentzeris, "Spiral resonators for optimally efficient strongly coupled magnetic resonance systems," Wireless Power Transfer J., Vol. 1, No. 1, 21-26, March 2014.
13. Choi, J. and C. H. Seo, "Analysis on transmission efficiency of wireless energy transmission resonator based on magnetic resonance," Progress In Electromagnetics Research M, Vol. 19, 221-237, 2011.
14. Komaru, T., M. Koizumi, K. Komurasaki, T. Shibata, and K. Kano, "Compact and tunable transmitter and receiver for magnetic resonance power transmission to mobile objects," Wireless Power Transfer — Principles and Engineering Exploration, K. Y. Kim, Ed., 130-150, InTech, 2012.
15. Jolani, F., J. Mehta, Y. Yu, and Z. Chen, "Design of wireless power transfer systems using magnetic resonance coupling for implantable medical devices," Progress In Electromagnetics Research Letters, Vol. 40, 141-151, 2013.
16. Li, C. J. and H. Ling, "A planarized, capacitor-loaded loop structure for wireless power transfer," IEEE Antennas Propag. Int. Symp., 840-841, Orlando, FL, July 2013.
17. Tierney, B. and A. Grbic, "Planar shielded-loop resonators," IEEE Trans. Antennas Propagat., Vol. 62, No. 6, 3310-3320, June 2014.
18. Sugiyama, H., "Performance analysis of magnetic resonance system based on electrical circuit theory," Wireless Power Transfer — Principles and Engineering Exploration, K. Y. Kim, Ed., 95-116, InTech, 2012.
19. FEKO Version 6.0, EM Software & Systems-S.A., Stellenbosch, South Africa, 2010 [Online].Available: http://www.feko.info, .
20. Di Paulo, F., Networks and Devices Using Planar Transmission Lines, 490-491, CRC Press LLC, Boca Raton, 2000.
21. Meissner, T. and F. J. Wentz, "The complex dielectric constant of pure and sea water from microwave satellite observations," IEEE Trans. Geosci. Remote Sens., Vol. 42, No. 9, 1836-1849, September 2004.