This section introduces the system configuration of the
13.56 MHz wireless power transfer system, whose block diagram
is shown in Fig. 1. The WPT system consists of a power
amplifier (AC source), a bidirectional coupler (power detection
for forward power and reflected power), a coupling system
(AC/AC), a full-bridge rectifier (AC/DC), a DC/DC converter
and various loads (resistor, batteries or supercapacitors). To
improve system efficiency, the goal is to minimize the reflected
power (Pf ). By analyzing coupling system, the optimum load
impedance (ZL) is first derived. Then optimum load of the
rectifier (RL) is determined by simulating the rectifier circuit,
whose input impedance is ensured to be ZL. At last, DC/DC
converter is designed to fulfill the requirement of rectifier.