▎ 摘　　要

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 sidestrips 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.