Focused microwave power transmission system with high-efficiency rectifying surface

A focused microwave power transmission (MPT) system with high-efficiency rectifying surface is proposed. This work has two main novel contributions: (i) most of wireless power transmission systems reported so far are non-focused. This study presents the first focused MPT system with circular polarisation; (ii) a novel high-efficiency rectifying surface using subwavelength resonant elements is developed. To design a focused transmitting array antenna with high power density at the receiving site and high beam collecting efficiency in the near field, a method based on the optimisation of a partial scattering matrix is employed. A left-handed circularly polarised microwave power rectifying surface consisting of 8 × 8 sub-wavelength resonant elements is designed and the measured conversion efficiency reaches 57.74%. To validate the concept, an experimental system including one focused transmitting array antenna and one 2 × 2 elements rectifying surface is implemented and measured, and the improvement of output direct current (DC) power and radiofrequency (RF)-to-DC conversion efficiency compared with non-focused condition is shown. The highest RF-to-DC efficiency of 66.5% is achieved in the focused mode, compared to that of 34.8% only in the non-focused mode as in traditional systems.