Design of Zero-Index Metasurface for Flexible Microwave Power Harvester

In this letter, an inkjet-printed and flexible zero-index metasurface for microwave power transmission (MPT) harvester is proposed and measured. The substrate and conductor are separately based on polyimide and liquid metal eutectic gallium indium (EGaIn) alloy in which the mass fractions of Ga and In are 75.5% and 24.5%, respectively. To accommodate the complex MPT application environment, such as the uneven surface of the receiving device and the movement of the harvesting target, the flexible energy harvester has received attention and research. However, in practical application, the condition of the harvester bending and the power oblique incidence will occur. Due to the decrease of the effective wave vector, the harvested power decreases. The designed zero-index metasurface can refract the obliquely incident energy wave so that the wave vector can pass through it and be transmitted vertically to improve this situation. The experimental results show that, at 5.8 GHz, the harvested power of the harvester with the zero-index metasurface is greatly improved when the incident angle increases and the bending degree increases.