We propose a dynamically tunable triple-band terahertz perfect absorber based on a monolayer graphene metasurface. The metasurface is composed of a graphene cross and four graphene side-strips on top of a metal film sandwiched by a dielectric spacer. Results show that there are three perfect absorption bands locating at 0.93 THz, 1.54 THz and 2.4 THz, showing near-unitary absorption of 99%, 98% and 99%, respectively. We find that these three perfect-absorption bands should originate from the resonances of the cross and of the four side-stripes. By varying the graphene chemical potential, the frequencies and the absorption efficiencies of all these three bands can be actively tuned. Additionally, we find these perfect-absorption bands are insensitive to the incident angle and the incident polarization, making the proposed absorber appealing in practical applications. We expect this work will advance the engineering of multiple-band terahertz perfect absorbers and will promote their applications in detectors and sensors.

我们提出了一种基于单层石墨烯超表面的动态可调三频太赫兹完美吸收体。超表面由石墨烯叉和在介电间隔层夹在中间的金属膜顶部的四个石墨烯侧条纹组成。结果表明，存在三个完美的吸收带，分别位于0.93 THz，1.54 THz和2.4 THz，分别显示了近单一吸收，分别为99％，98％和99％。我们发现这三个完美吸收带应该来自交叉和四个侧条纹的共振。通过改变石墨烯的化学势，可以主动调节所有这三个谱带的频率和吸收效率。此外，我们发现这些完美吸收带对入射角和入射极化不敏感，使所提出的吸收器在实际应用中具有吸引力。我们希望这项工作将促进多频带太赫兹完美吸收体的工程设计，并将促进其在探测器和传感器中的应用。