A Tree-Ring-Inspired Tunable Flexible Near-Zero-Index Metasurface for Microwave Power Transmission

In emerging fields such as the Internet of Things (IoT), wearable devices, and smart sensing, reliable wireless power delivery is of paramount importance. However, traditional microwave power transmission (MPT) systems often face a sharp decline in energy harvesting efficiency when subjected to oblique electromagnetic wave incidence or mechanical deformation of the receiver. To address this bottleneck, this study proposes and designs a flexible near-zero-index metasurface (FNZIM). This metasurface can precisely control the wave vector to guide the energy. By integrating the FNZIM with a flexible energy harvester, we constructed a microwave power harvesting system that remained highly efficient even in complex environments. Experimental results demonstrate a significant improvement in the harvesting efficiency of the integrated system compared to a stand-alone harvester, with the peak efficiency exceeding 80% under aggravated oblique incidence or bending. This fully validates the effectiveness and feasibility of using an FNZIM to enhance the performance of microwave energy harvesters in wide-angle and conformal application scenarios, offering an innovative solution for wireless power delivery to flexible electronic devices and IoT sensors.