By sweeping the load resistance in Fig. 5, the system
efficiency curve and power reflection coefficient are plotted
in Fig. 6. The simulation results show that when the load
resistance equals to 95 Ω, a maximum efficiency of 76% can
be achieved, and the power reflection can be reduced to 5%.
In the impedance analysis for coupling system, it is required
that ZL = 73 Ω, which is the input impedance of the rectifier.
However when RL = 95 Ω, ZL equals to (55-27*j) Ω,
which means the mismatch between rectifier and coupling
system cannot be completely resolved by adjusting RL. If an
ideal impedance matching network is added to tune ZL from
(55-27*j) Ω to 73 Ω in ADS, the system efficiency can be
improved from 76% to 81%. However when the impedance
matching network is simulated using practical inductor and
capacitor model, the system efficiency drops to 78%. Because
impedance matching networks require extra components and
will inevitably cause power loss, it is a trade-off between
system efficiency and system complexity. In this paper, a
wireless power transfer without impedance matching networks
is proposed.