Wireless Power Transfer (WPT) based on resonant magnetic coupling is an attractive technology for enabling the wireless recharge of electric devices and systems. One of the main drawbacks of this technology is related to the dependence of the efficiency and the power delivered to the load on possible variations of the coupling coefficient and load impedance. In order to alleviate the effects of this dependence, the optimization of appropriate adaptive matching networks is proposed in this paper. The three power gains usually adopted in the context of two-port active networks are assumed as figures of merit in the optimization process. It is theoretically and experimentally demonstrated that the maximum realizable gain of the link is achieved when the conjugate image impedance matching is realized by appropriate matching networks at both the input and output ports of the WPT link.
2. Imura, T. and Y. Hori, "Maximizing air gap and efficiency of magnetic resonant coupling for wireless power transfer using equivalent circuit and neumann formula," IEEE Transactions on Industrial Electronics, Vol. 58, No. 10, 4746-4752, 2011.
3. Sample, A. P., D. T. Meyer, and J. R. Smith, "Analysis, experimental results, and range adaptation of magnetically coupled resonators for wireless power transfer," IEEE Transactions on Industrial Electronics, Vol. 58, No. 2, 544-554, 2011.
4. Zargham, M. and P. G. Gulak, "Maximum achievable efficiency in near-field coupled power-transfer systems," IEEE Transactions on Biomedical Circuits & Systems, Vol. 6, No. 3, 228-245, 2012.
5. Dionigi, M., M. Mongiardo, and R. Perfetti, "Rigorous network and full-wave electromagnetic modeling of wireless power transfer links," IEEE Transactions on Microwave Theory and Techniques, Vol. 63, No. 1, 65-75, Jan. 2015.
6. Monti, G., W. Che, Q. Wang, A. Costanzo, M. Dionigi, F. Mastri, M. Mongiardo, R. Perfetti, L. Tarricone, and Y. Chang, "Wireless power transfer with three-ports networks: Optimal analytical solutions," IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 64, No. 2, 494-503, Feb. 2017.
7. Kim, J., D. H. Kim, and Y. J. Park, "Analysis of capacitive impedance matching networks for simultaneous wireless power transfer to multiple devices," IEEE Transactions on Industrial Electronics, Vol. 62, No. 5, 2807-2813, 2015.
8. Kim, N. Y., K. Y. Kim, J. Choi, and C. W. Kim, "Adaptive frequency with power-level tracking system for efficient magnetic resonance wireless power transfer," Electronics Letters, Vol. 48, No. 8, 452-454, 2012.
9. Mastri, F., A. Costanzo, and M. Mongiardo, "Coupling-independent wireless power transfer," IEEE Microwave and Wireless Components Letters, Vol. 26, No. 3, 222-225, 2016.
10. Yang, Y., Y. Luo, S. Chen, and X. Wen, "A frequency-tracking and impedance-matching combined system for robust wireless power transfer," International Journal of Antennas and Propagation, 1-13, 2017.
11. Lee, J., Y. Lim, H. Ahn, J.-D. Yu, and S.-O. Lim, "Impedance-matched wireless power transfer systems using an arbitrary number of coils with exible coil positioning," IEEE Antennas and Wireless Propagation Letters, Vol. 13, 1207-1210, 2014.
12. Hoang, H., S. Lee, Y. Kim, Y. Choi, and F. Bien, "An adaptive technique to improve wireless power transfer for consumer electronics," IEEE Transactions on Consumer Electronics, Vol. 58, No. 2, 327-332, 2012.
13. Cannon, B. L., J. F. Hoburg, D. D. Stancil, and S. C. Goldstein, "Magnetic resonant coupling as a potential means for wireless power transfer to multiple small receivers," IEEE Transactions on Power Electronics, Vol. 24, No. 7, 1819-1825, 2009.
14. Xue, R.-F., K.-W. Cheng, and M. Je, "High-efficiency wireless power transfer for biomedical implants by optimal resonant load transformation," IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 60, No. 4, 867-874, 2013.
15. Beh, T. C., T. Imura, M. Kato, and Y. Hori, "Basic study of improving efficiency of wireless power transfer via magnetic resonance coupling based on impedance matching," 2010 IEEE International Symposium on Industrial Electronics (ISIE), 2011-2016, IEEE, 2010.
16. Beh, T. C., M. Kato, T. Imura, S. Oh, and Y. Hori, "Automated impedance matching system for robust wireless power transfer via magnetic resonance coupling," IEEE Transactions on Industrial Electronics, Vol. 60, No. 9, 3689-3698, 2013.
17. Lim, Y., H. Tang, S. Lim, and J. Park, "An adaptive impedance-matching network based on a novel capacitor matrix for wireless power transfer," IEEE Transactions on Power Electronics, Vol. 29, No. 8, 4403-4413, 2014.
18. Waters, B. H., A. P. Sample, and J. R. Smith, "Adaptive impedance matching for magnetically coupled resonators," PIERS Proceedings, 701, Moscow, Russia, Aug. 19–23, 2012.
19. Kiani, M., U.-M. Jow, and M. Ghovanloo, "Design and optimization of a 3-coil inductive link for efficient wireless power transmission," IEEE Transactions on Biomedical Circuits and Systems, Vol. 5, No. 6, 579-591, 2011.
20. Nikoletseas, S., Y. Yang, and A. Georgiadis, Wireless Power Transfer Algorithms, Technologies and Applications in Ad Hoc Communication Networks, Springer, 2016.
21. Mastri, F., M. Mongiardo, G. Monti, M. Dionigi, and L. Tarricone, "Gain expressions for resonant inductive wireless power transfer links with one relay element," Wireless Power Transfer, 2017.
22. Mastri, F., M. Mongiardo, G. Monti, and L. Tarricone, "Characterization of wireless power transfer links by network invariants," International Conference on Electromagnetics in Advanced Applications, 590-593, 2017.
23. Collin, R. E., Foundations for Microwave Engineering, McGraw-Hill, 1992.
24. Kurokawa, K., "Power waves and the scattering matrix," IEEE Transactions on Microwave Theory and Techniques, Vol. 13, No. 2, 194-202, 1965.
25. Roberts, S., "Conjugate-image impedances," Proceedings of the IRE, Vol. 34, No. 4, 198-204, 1946.
26. Frickey, D. A., "Conversions between s, z, y, h, abcd, and t parameters which are valid for complex source and load impedances," IEEE Transactions on Microwave Theory and Techniques, Vol. 42, No. 2, 205-211, Feb. 1994.
27. Niu, W.-Q., J.-X. Chu, W. Gu, and A.-D. Shen, "Exact analysis of frequency splitting phenomena of contactless power transfer systems," IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 60, No. 6, 1670-1677, 2013.
28. Costanzo, A., W. Che, M. Dionigi, F. Mastri, M. Mongiardo, G. Monti, L. Tarricone, and Q. Wang, "Matched resonant inductive WPT using the coupling-independent regime: Theory and experiments," Proc. of the European Microwave Conference (EuMC), 204-207, 2017.
29. Monti, G., A. Costanzo, F. Mastri, M. Mongiardo, and L. Tarricone, "Rigorous design of matched wireless power transfer links based on inductive coupling," Radio Science, Vol. 51, No. 6, 858-867, Jun. 2016.
30. Bowick, C., RF Circuit Design, Sams, 1982.
31. Van Bezooijen, A., M. A. de Jongh, F. van Straten, R. Mahmoudi, and A. H. M. van Roermund, "Adaptive impedance-matching techniques for controlling L networks," IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 57, No. 2, 495-505, 2010.