▎ 摘　　要

Tunable conductivity of graphene, makes it a promising material for metamaterials. There are various graphene tunable metamaterial absorbers in the mid-infrared region, whose absorption spectrum can be dynamically tuned by varying the Fermi potential of graphene. However, graphene absorbers working in the low mid-infrared region (4-7 mu m) has limited tuning. In this work, the spectral tuning efficiency of a graphene based metal disc pattern and a graphene ribbon pattern metamaterial absorber is studied using FDTD simulation. The tunability in absorption spectrum achieved by metal disc absorber is 2-4%, which increased to 5-20% for graphene ribbon absorber with more than 85% absorption rate. Thus, the graphene pattern absorber significantly improves the tunability and provides broad tuning in 4-7 mu m wavelength range. However, the graphene ribbon absorber is polarization dependent due to its non-symmetric shape. Hence, a new type of nano square hole (NSH) graphene absorber is proposed, which can easily be externally biased and provide polarization independent absorption. The NSH graphene absorber has wide tunability of 5-20% and high absorption rate of 85% similar to the graphene ribbon absorber. These results are very helpful to design tunable sensors and multispectral devices for gas sensor and biosensor applications.