Multitarget Wireless Power Transfer System Strategy Based on Metasurface-Holography Multifocal Beams

Aiming at the critical problem of wireless power transfer (WPT) for the current growing number of wireless devices, the multitarget WPT system based on metasurface-holography multifocal beams and the design methods is investi-gated and analyzed in this article. As the propagator in near-field synthesis, a new field calculation formula is derived based on the Friis formula between the metasurface unit (MU) and the field point, which breaks the limitation of paraxial approximation and makes metasurface holography applicable in a wide-angle, long-distance, and nonplane space. Besides the phase response of MUs, the amplitude response is also introduced, which achieves the simultaneous amplitude-phase optimization of the metasurface to improve transmission efficiency. A metasurface with holography multifocal beams is first designed and engaged in forming a planar multitarget WPT system, which has been proven to radiate the designed multifocal beam and transfer power to each focal spot uniformly and efficiently after simulated, fabricated, and measured. To verify that the proposed method can achieve a near-field synthesis of multifocal beams in nonplane space over a wide angular range, a metasurface with 23-focus beam distribution on a spherical surface with an elevation angle from -60 degrees to 60 degrees, omnidirectional azimuth, and 66.67 lambda radius is designed and simulated, which shows that the simulated radiation field distribution is in good agreement with the initial preset target field. This work demonstrates a feasible high-efficiency and long-distance WPT strategy for multiple targets in wide-angle and spatial scenarios.