  Metasurface has witnessed an urgent need for reconfigurable chiral
manipulation recently, while the graphene-based devices attracted significant
attention from researchers due to their inherent tunable properties. Here, an
L-shaped metasurface composed of three hollow monolayer graphene resonant rings
is proposed. A huge dual-frequency asymmetric transmission (AT) in the
mid-infrared band (7800 nm-9000 nm) with transmission efficiency peaks of 0.14
and 0.26 is revealed, which is optimal of its similar monolayer counterparts in
the current band. By changing the Fermi level of graphene and the relaxation
time of its carriers, the AT spectrum including the positions and widths of the
peaks can be effectively modulated. More importantly, the structure designed
here gives priority to the machinability of the metasurface configuration,
ensuring its practicality and promising applications in chiral applications in
the future.
