This work demonstrated a metamaterial array with polarization-insensitive and wide-angle operating in triple-band (GSM 1800, WiMAX, WLAN). The cell of the array consists of four same Split-Ring Resonators arranged in rotating central symmetry. The structure and size of the metamaterial cell were analyzed and optimized by using the microwave simulation software of CST. Meantime, we studied the absorption efficiency and harvesting efficiency under the normal and oblique incidences, energy distribution on the cell and the surface current paths. The simulation results show that the harvesting efficiency is 30%, 90%, and 74% at 1.75 GHz, 3.8 GHz, and 5.4 GHz, respectively, on the conditions of random polarization and the normal incidence. When the oblique incidence changes from 0° to 45°, this meta-harvester can also maintain effective harvesting efficiencies in triple-band. A 7 × 7 array has been fabricated and measured, and a good agreement with the simulated results was obtained.

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Although germanium-and silicon-based detectors have been commercialized for NIR photodetection, [4,5] their response speeds and sensitivities still have potential for improvement. It has also been reported that 2D materials have great potential for application in low-cost, room temperature, and large-area visible-near-infrared (VIS-NIR) photodetection applications owing to their excellent optical and electronic properties, [6][7][8][9][10][11][12] and various VIS-NIR photodetectors based on 2D materials have been reported. For example, graphene has been demonstrated to exhibit a rapid photoresponse; however, its lack of a bandgap, low light absorption properties, and low intrinsic sensitivity hinder its potential applications in VIS-NIR detection. [13,14] As alternatives, transition metal dichalcogenides (TMDs) exhibit large bandgaps for infrared detection, [15,16] and black phosphorus (BP) exhibits a good performance in infrared photodetection owing to its suitable bandgap and fast carrier mobility; [17,18] however, the latter suffers from a poor air stability. Furthermore, despite the fact that heterostructure photodetectors have been shown to exhibit high performances, they require complex transfer processing. [19][20][21] Considering the above systems, it is therefore apparent that the development of suitable VIS-NIR-responsive materials would be highly attractive.In this context, Bi 2 O 2 Se has recently attracted increasing attention because of its suitable electronic bandgap (≈0.8 eV), high carrier mobility (≈450 cm 2 V −1 s −1 at 300 K), excellent air stability, high conductivity, and environmental non-toxicity, which render it an ideal candidate for VIS-NIR detection. [22][23][24][25][26][27][28] However, its high carrier concentration leads to a large dark current in detectors based on Bi 2 O 2 Se nanosheets, which restricts any further performance improvement being achieved. To address this issue, previous studies have examined the use of gate voltage regulation [29,30] and heterostructure construction. [31][32][33] However, the application of extremely high gate voltages increases the power consumption of the device, and the construction of heterostructures often requires complex transfer processes. In addition, the reported Bi 2 O 2 Se photodetectors tend to show poor response speeds in the NIR waveband (i.e., tens of milliseconds), which limits their application in high-speed detection. [27,34] Owing to its suitable electronic bandgap, excellent air stability, and high carrier mobility at room temperature, low-dimensional bismuth oxyselenide (Bi 2 O 2 Se) has become attractive in the context of visible-near-infrared (VIS-NIR) detection. However, the high carrier concentration and bolometric effect of Bi 2 O 2 Se nanosheets are not conducive to reducing the dark current and improving the response speed, which hinders Bi 2 O 2 Se nanosheet-based photodetectors from achieving an optimal performance. In this study, a Bi 2 O 2 Se nanoribbon is controllably synthesized on a fluorophlogopite substrate by m...

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