Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless non-radiative power-transfer (WNPT) systems. Closed-form expressions for the efficiencies of both types of systems are presented as functions of frequency and system (circuit) parameters. 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. Frequency-tuning 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 to achieve a simultaneous conjugate impedance match over a range of distances. The frequency-tuned system is simpler to implement, while the impedance-tuned system is more complex, but can achieve higher efficiencies. Both of the experimental wireless non-radiative power-transfer systems studied employ resonant shielded loops as transmitting and receiving devices.