Miniaturized Polarization-Insensitive Rectifying Metasurface for Powering Internet of Things Devices

In this letter, a miniaturized polarization-insensitive rectifying metasurface unit cell is proposed for powering electric devices of Internet of Things. The metasurface, an array of periodic unit cells, consists of two layers of substrate and three layers of metal. The metasurface unit cell is composed of eight asymmetric dipoles, which are arranged orthogonally and closely on both surfaces of the upper substrate. The strong coupling between dipoles induces extra reactive components, which makes the unit size be miniaturized to only 0.15λ₀. The miniaturization mechanism is analyzed by the equivalent circuit theory. The simulation results show that the harvesting efficiency for arbitrary polarized waves is higher than 90% from 2.2 to 2.7 GHz (20%). Being integrated with Schottky diodes in the proper position, the rectifying metasurface is designed. A 2 × 2 array with the size of 0.3λ₀ × 0.3λ₀ was fabricated and measured. The maximum harvesting-rectifying efficiency is 61% at 2.45 GHz under different polarization angles. When the power density is 8 mW/cm², 80 mW direct current power could be obtained.