Heebl, J. D., Thomas, E. M., Penno, R. P., & Grbic, A. (2014). Comprehensive analysis and measurement of frequency-tuned and impedance-tuned wireless non-radiative power-transfer systems. IEEE Antennas and Propagation Magazine, 56(4), 44-60.
This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless nonradiative power transfer (WNPT) systems. Closed-form expressions for the efficiencies of both systems, as a function of frequency and system (circuit) parameters, are presented. In the frequency-tuned system, the operating frequency is adjusted to compensate for changes in mutual inductance that occur for variations of transmitter and receiver loop positions. Frequencytuning is employed for a range of distances over which the loops are strongly coupled. In contrast, the impedance-tuned system employs varactor-based matching networks to compensate for changes in mutual inductance and achieve a simultaneous conjugate impedance match over a range of distances. The frequencytuned system is simpler to implement, while the impedance-tuned system is more complex but can achieve higher efficiencies. Both of the experimental WNPT systems studied employ resonant shielded loops as transmitting and receiving devices.