  In this paper, we present a 5.8 GHz radio-frequency (RF) wireless power
transfer (WPT) system that consists of 64 transmit antennas and 16 receive
antennas. Unlike the inductive or resonant coupling-based near-field WPT, RF
WPT has a great advantage in powering low-power internet of things (IoT)
devices with its capability of long-range wireless power transfer. We also
propose a beam scanning algorithm that can effectively transfer the power no
matter whether the receiver is located in the radiative near-field zone or
far-field zone. The proposed beam scanning algorithm is verified with a
real-life WPT testbed implemented by ourselves. By experiments, we confirm that
the implemented 5.8 GHz RF WPT system is able to transfer 3.67 mW at a distance
of 25 meters with the proposed beam scanning algorithm. Moreover, the results
show that the proposed algorithm can effectively cover radiative near-field
region differently from the conventional scanning schemes which are designed
under the assumption of the far-field WPT.
