Figure 4.

The IWPT system performance when IMN is a series resonant capacitor. $R_{sd}=R_{tx}+R_{tr}$. The supply voltage is constant as $V_s=5$ V. ${\eta }_{link+reg}$ represents the power efficiency assuming that the redundant power delivered to load is wasted on regulator. When system is in region B and C in the figure, the output power is higher than the load needed power level. This redundant power would be wasted at the load side which decreases the efficiency. In region A, there is no redundant power loss at load side, but the output power is less than needed.