Based on the theory explained earlier, an automated IM system
is designed to match the resonators in the MRC-based WPT
system. Fig. 5 shows the diagram of the proposed automated IM
system. The system transfers the power from the 13.56-MHz
power source to the load through the two resonators with an
identical self-resonance frequency. The power is transferred
through MRC between the resonators, and it is rectified to
charge energy storage mediums such as batteries. The characteristic
impedance of the power source and the Bayonet
Neill–Concelman cables are 50 Ω in this paper. Under normal
circumstances, the coupling coefficient k (affected by the gap)
between the resonator and the impedance of the load (50 Ω in
this paper) is unknown and variable. Only the voltage, current,
and wave reflection ratio can be measured in the transmitting
side of the system.
In the proposed system, a directional coupler is inserted
between the power source and the transmitting resonator to
measure S11, the ratio of power that is reflected from the
resonators back to the power source. The measured values are
input into a computer which is used to control the parameters
of the IM circuit. The main advantage of using the directional