A Hybrid RF and Solar Integrated Energy Harvesting System Using Optically Transparent Metasurface

A hybrid energy harvesting scheme and system integrating radio frequency (RF) electromagnetic wave and solar energy based on optically transparent metasurface is proposed and constructed for the first time in this article. The scheme combines the RF link and the solar link through the high-efficiency transparent metasurface and rectifier circuit, the solar cell, and the power management circuit. To improve the efficiency of RF energy harvesting, the transparent rectangular metal mesh and the corresponding transparent substrate are combined with metasurface for the first time. Therefore, the loss is effectively reduced and the simulation results show that the scheme improves the efficiency of RF energy harvesting by 20% compared with traditional indium-tin oxide (ITO) thin film devices. Then, the metasurface is optimized with capacitance enhancement design, which uses additional multicross branches to improve the radiation efficiency and the stability of the incident angle, and the metasurface can harvest about 50% of the energy in the vertical direction at ±45°. To construct the system, a transparent metal mesh feed network with low port impedance is designed and integrated with the metasurface so that the inability of mesh lines to simulate high impedance is overcome and the system space is reduced. Also, a 5.8-GHz high-efficiency rectifier circuit is then designed to convert the RF energy harvested by the metasurface into dc, which has a measured rectification efficiency of 68.7%. The designed energy harvesting metasurface has the theoretical and measured transparency of 97.7% and 89.4%, respectively, and the energy harvested by the metasurface and solar energy is mixed through the BQ25504 device to obtain the final energy, which can be widely used to achieve all-weather charging for wireless power devices and sensor networks.