▎ 摘　　要

Reflective metasurfaces for arbitrary wave-front control require unit cells to achieve both 2 pi phase rotation and unity amplitude in reflection waves, and such requirements are a fundamental challenge for ultra-thin metasurfaces without the use of a metallic plate. We analytically show that in two coupled resonators, tuning the resonance frequency with the external decay rate for one of the resonators enables near 2 pi phase rotation and unity amplitude in the reflection wave, where no reflector is required. We implement the mechanism on a reflective graphene metasurface with its thickness being less than a 0.03 free space wavelength. As an illustration, we numerically demonstrate that in a wireless communication scenario, the actively tunable graphene metasurface is able to reflect an incident wave to a receiver or be transparent for an incident wave, which is the significant advantage arising from the structure without a metallic plate. In addition, the loss effect of the metasurface on the performance is discussed in terms of the conductive loss of graphene and the deviation of the reflection phase from a desired distribution. Our results open up opportunities for reflective metasurfaces without a metallic plate.