Nanoscale
Advances
Lin Peng, Xiao-ming Li, Xiao Liu, Xing Jiang, Si-min Li
https://pubs.rsc.org/en/content/articlepdf/2019/na/c8na00149a?page=search
Terahertz electromagnetic (EM) wave absorbers are vital in photonics, however, they suffer from limited
bandwidth. A new approach for ultra-wideband (UWB) terahertz absorber design is proposed with metal
and graphene metasurfaces. The UWB characteristics are owing to three factors: (1) the metal
metasurface boosts the surface plasmon-polaritons (SPPs) of the graphene metasurface which leads to
confined field enhancement, (2) the merging and interaction of the resonances of the metal and
graphene metasurfaces, and (3) the multiple reflections and superpositions between the metasurfaces
and the gold layer. A prototype designed using a dual-ring metal metasurface, fishnet graphene
metasurface, polyimide substrate and gold reflecting layer is proposed. One cell of the prototype
includes one metal dual-ring unit and four graphene fishnet units. The proposed absorber has an UWB
bandwidth of 6.46 THz (145%) for absorptivity larger than 0.9, with a high octave of 6.21. The proposed
absorber is also insensitive to the polarization state and incident angle of the illuminating EM waves.
Besides, the amplitude modulation depth in the 5–6 THz band is up to 95.4%. The physical mechanisms
of the wideband operation are also discussed. The research in this work could offer a new thought for
UWB absorber design, and has potential applications in terahertz imaging, sensors, photodetectors and
modulators
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