Wireless Power Transfer in the Radiative Near Field

A scheme for wireless power transfer (WPT) in the radiative near-field (Fresnel) region is presented. The proposed Fresnel WPT scheme is designed to focus microwaves to a diffraction-limited region where a detector can be positioned, achieving reasonably high power transfer efficiency over moderate distances. The configuration consists of transmit and receive microstrip patch array antennas, with the receiving antenna connected to a power-harvesting half-wave rectifier (rectenna). Fresnel region operation enables the fields radiated by the transmitting aperture to be localized both in range and cross-range. Using Fresnel region focusing, we achieve an increase of 66.8% in the amount of received power when compared to the performance of a conventional beamforming array. We also demonstrate the efficiency improvement by powering an LED using the on-axis and off-axis focusing configurations.