  To increase the transmission distance of Wireless Power Transfer (WPT)
systems, we provide guidelines on choosing the optimal location of an
Intermediate Coil with respect to size within a standard five-coil axially
aligned experimental setup. From our results, for maximum magnitude of S21 at
the resonant frequency we found the optimal location to exist where the
coupling coefficient between the Transmitter and the Intermediate Coil and the
coupling coefficient between the Receiver and the Intermediate Coil are
identical. Additionally, the optimal outer diameter for the maximum magnitude
of S21 at the resonant frequency of the Intermediate Coil in the given
symmetric and asymmetric setup are found to be larger than both TX and RX.
