Design and Implementation of 5.8 GHz RF Wireless Power Transfer System

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, with the proposed beam scanning algorithm, the power transfer efficiency reaches 20.32 % and 0.24 % at distances of 0.5 and 5 meters, respectively, whereas the far-field-only-scanning scheme achieved the transfer efficiencies of 13.45 % and 0.23 % at the same receiver positions. Since the proposed transmit antenna array has the maximum linear dimension of 299.12 mm, the approximate boundary between far-field and radiative near-field is 3.45 meters based on the Fraunhofer distance calculation. 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.