Rectifying surface with optimal RF-to-DC efficiency insensitive to polarisation collimation

A rectifying surface for energy harvesting with optimal RF-to-DC efficiency insensitive to polarisation collimation is presented based on metasurface and branch-line coupler. The metasurface captures two orthogonal components of incident wave by two separate loads with high efficiency. A 90° branch-line coupler is introduced to redistribute two polarisation-dependent components into two invariant equipower outputs, aiming to preserve continuous impedance-matching between metasurface and rectifiers for maximised conversion efficiency. The proposed rectifying surface has been fabricated and measured. The measured fluctuation ranges of capture and conversion efficiency are smaller than 2 and 0.5%, respectively, agreeing well with authors’ prediction. They expect a wide range of applications to emerge from this novel concept in the future.