Abstract—Recent research in wireless power transfer (WPT)
using resonant inductive coupling has demonstrated very high
efficiencies (above 40%) at large distances compared to the
transmitting element dimensions, thereby exponentially increasing
the number of potential applications of WPT. Since resonant
inductive coupling is a very multidisciplinary field, different
approaches have been proposed to predict the behaviour of these
systems from the physical theory of resonators (coupled-mode
theory), reflected load theory and circuit theory. Also, there is
in this field a heterogeneous definition of metrics without a clear
optimization process. In this article we unify the different metrics
and demonstrate how to maximize the power transfer efficiency
in a non-radiative resonant wireless power transfer link from
a circuit-centric point of view providing design guidelines in
terms of optimal load impedance, optimal source impedance and
optimal distance between coils.