Ultra-thin Energy Harvesting Metasurface with Polarization-insensitive and Wide-angle-of-incident Performance

Achieving an ultrathin and polarization-insensitive energy harvester is highly desirable and essential for modern wireless receiving systems. However, currently available energy harvesters still face challenges related to the bulkiness of the system or limitations to specific polarized electromagnetic (EM) waves. In this paper, a proposal for an ultra-thin metasurface energy harvester (MEH) operating within the 5.75 GHz ~ 5.85 GHz frequency range (WIFI) has been presented. The MEH exhibits polarization insensitivity and wide incidence angle characteristics, distinguishing it from traditional energy harvesters. The MEH unit comprises a patch, substrate, and ground, with the substrate featuring two vias and sandwiched between the patch and ground. The patch connects to the ground plane through two lump resistors of 100 ohms and vias, as illustrated in Fig. 1. The substrate material chosen is Rogers RO4350B (ε
r
= 3.66, tan δ = 0.0037) with an ultra-thin thickness of t = 0.254 mm, and the metal layers are made of copper with a thickness of 0.035 mm. The unit structure is based on a half-wave dipole antenna, and its impedance is meticulously designed to align with free space impedance, ensuring high-efficiency energy transfer with increased flow to the load through the vias. The polarization insensitivity is attributed to the completely centrosymmetric metal patch structure, enabling nearly constant absorption efficiency and energy harvesting efficiency across different polarization angles. Simulation results indicate that, within the polarization angle range of 0° ∼ 90° at vertical incidence, the absorption efficiency and energy harvesting efficiency consistently surpass 99.4% and 82.5% at 5.82 GHz, respectively. Particularly at 0° (transverse magnetic polarization, TM) and 90° (transverse electric polarization, TE), the absorption efficiency and energy harvesting efficiency reach 99.2%, 85.3%, and 99.3%, 83.5%, respectively. In addition, the absorption efficiency and energy harvesting efficiency under different incident angles were also studied. The simulation results show that the absorption efficiency and harvesting efficiency are maintained above 80.2%, 70.1%, and above 90.1%, 80.3% for TE and TM waves in the range of 0° ∼ 60° incident angle, respectively.