A Flexible and Polarization-Insensitive Metasurface Harvester Featuring a Dual-Ring Unit with a T-Shaped-Gap Outer Ring for Microwave Power Transfer

This paper proposes a flexible and polarization-insensitive metasurface (MS) operating at the 5.8 GHz band for electromagnetic energy harvesting. The proposed MS unit features a top-layer dual-ring resonator with a T-shaped gap and a bottom cross-shaped coplanar waveguide (CPW), fabricated on a flexible polyimide substrate. To elucidate the physical mechanism of energy capture, an equivalent circuit model is established based on transmission line theory. Expressions for the total input impedance are derived, revealing the quantitative relationship between the structural parameters and the impedance-matching condition. The simulation results validate this theoretical model and show that the structure achieves an absorption efficiency of 97.5% and a harvesting efficiency (HE) of 86.6% at 5.72 GHz. The conversion efficiency remains above 50% over a wide range of incident angles, and the HE exhibits minimal variation within a polarization angle range of 0-90°. Experimental results indicate that the MS reaches a maximum HE of 73.2%, maintains over 40% efficiency under large-angle incidence, and achieves more than 65% HE across various curved surfaces. With its mechanical flexibility, polarization insensitivity, and simplified manufacturing, this MS harvester provides a reliable and scalable power solution for wireless power transfer applications.