This paper reports the design, fabrication, and measurement of a metasurface with wide-angle-reception and polarization-insensitive characteristics for harvesting electromagnetic energy. Unlike the metasurface unit cell with multiple vias reported in the literature, it realizes polarization-insensitive characteristics using a single via, which reduces the complexity of the structure significantly. The harvesting and absorption efficiencies at the normal and oblique incidences, energy distribution, and the surface current for different polarization angles are investigated. The simulation results show that the maximum harvesting efficiency is 88% at the center frequency of 5.8 GHz for the arbitrary polarization at the normal incidence of 0°. Within the oblique incidence range of 75°, the maximum efficiency remains higher than 77% for the random polarization. A 5 × 5 array has been fabricated and measured, and the good agreement with the simulated results is obtained.

In this work, we introduced the design, demonstration, and discussion of a wideband metamaterial array with polarization-independent and wide-angle for harvesting ambient electromagnetic (EM) energy and wireless power transfer. The array consists of unit cells with one square ring and four metal bars. In comparison to the published metamaterial arrays for harvesting EM energy or wireless transfer, this design had the wide operation bandwidth with the HPBW (Half Power Band Width) of 110% (6.2 GHz–21.4 GHz), which overcomes the narrow-band operation induced by the resonance characteristic of the metamaterial. On the normal incidence, the simulated maximum harvesting efficiency was 96% and the HPBW was 110% for the random polarization wave. As the incident angle increases to 45°, the maximum efficiency remained higher than 88% and the HPBW remained higher than 83% for the random polarization wave. Furthermore, the experimental verification of the designed metamaterial array was conducted, and the measured results were in reasonable agreement with the simulated ones.

In this paper, a miniaturized polarization-insensitive rectifying metasurface unit cell is proposed for powering electric devices of Internet-of-Things (IoT). 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 0.15 λ ₀ . The miniaturization mechanism is analyzed by the equivalent circuit theory. The simulation results show that the harvesting efficiency for arbitrary polarized waves are higher than 90% from 2.2 to 2.7 GHz (20%). Being integrated with Schottky diodes at the proper position, the rectifying metasurface is designed. A 2 × 2 array with the size of 0.3 λ ₀ × 0.3 λ ₀ 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/cm ² , 80 mW direct current (DC) power could be obtained.

In this paper, a broadband polarization-insensitive rectifying metasurface unit with wide-reception-angle is proposed for powering battery-free sensors. To extend the bandwidth, two orthogonal stair-shaped dipoles (SS-dipole) with a wide impedance bandwidth are proposed as the unit. The vertical SS-dipole operates as dominating dipole to generate a resonant frequency of 5 GHz, while the horizontal one works as the parasitic one to excite 6.7 GHz. Thereby the operation band is from 4.6 to 7 GHz (41%), which covers the n79, LTE band46 and Wi-Fi band. An equivalent circuit is established to reveal the broadband operation principle. Furthermore, two SS-dipoles interact as the dominating and parasitic dipoles at two orthogonal polarizations, so polarization-insensitive performance is realized. By conjugate matching the unit with the rectifying diode, the rectifying metasurface is designed. A 5 × 5 array is fabricated and the measured harvesting-rectifying efficiency is higher than 45% within the operation band with the peak one of 63% at 5 GHz. The efficiency is higher than 50% when the incident angle is 48°.

Simultaneous wireless information and power transfer (SWIPT) with a power-splitting (PS) scheme has been extensively studied for Internet of Things (IoT) applications. However, the PS scheme usually employs a power divider or hybrid coupler for splitting the radio frequency (RF) signal, which makes the receiver structure complex and introduces extra losses. To address this challenge, we propose a novel PS scheme for SWIPT using a shared aperture metasurface (SAM). The SAM includes a rectifying metasurface on the first substrate layer and a communication metasurface antenna (meta-antenna) on the second one. The rectifying metasurface can harvest most RF signals as energy and transmit a small portion for communication, whose ratio can be adjusted by the etched gap width between two substrate layers. A prototype with 8.5:1 ratio of energy to information is designed and fabricated. The measured results show that the rectifying metasurface has a radio frequency (RF) to direct current (DC) conversion efficiency over 50% at any polarization direction within a wide reception range of 45∘ oblique incidence. A maximum data rate of 350 Mbps for 128-QAM is measured when bit error rate (BER) is lower than 10-6 and signal-to-noise ratio (SNR) is lower than -30 dB. An SWIPT system demonstration employing the proposed SAM for environmental monitoring sensor nodes is presented. When sensors receive the RF signal from the transmitter, they can convert it to DC power for self-powering and send the environmental data back to the transmitter.