Design and Validation of Reconfigurable Reflectarray for Sub-GHz Wireless Power Transfer

The paper presents an experimental study on a reconfigurable reflectarray (RRA) design suitable for wireless power transfer (WPT) in the sub-GHz range. The RRA’s capability to redirect the power of the incident wave enables one to deploy a self-adaptable power transfer channel to reduce the effect of path loss on the overall WPT system’s power transfer efficiency. The RRA under study employs varactor diode-loaded metal patches acting as voltage-controlled resonant phase shifters. An RRA prototype comprising 36 geometrically identical phase shifters, each formed by a pair of 8-shaped metallic patches, was fabricated. The metal patches are coupled via varactor diodes to achieve local RRA phase profile alteration by varying diode bias voltages. The phase shifters are printed on several standard FR-4 PCBs, reducing manufacturing costs, which is of primary importance due to their relatively large footprint. The developed RRA can be seamlessly integrated with other WPT-enhancing techniques, such as the multi-hop node technique recently proposed by the authors. To verify the feasibility of the developed RRA, the received power is measured at different angles and for different RRA configurations (desired reflection angles). Each configuration represents a set of varactor diode bias voltages generated to achieve a phase profile, ensuring the power reflection in a desired direction away from the RRA surface. The measured received power is compared with that reflected from a large flat metallic sheet, utilized as a reference reflector, to evaluate the RRA reflection efficiency. The obtained results show that the RRA ensures a reasonably high reflection efficiency. In all the cases examined, the RRA outperforms the metallic sheet in terms of the amount of received power. The reflected energy from the RRA can be used to charge low-power sensor nodes remotely.