Tunability in Graphene Based Metamaterial Absorber Structures in Mid-Infrared Region

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 μm) 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 μm 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.