Tunable plasmon-induced transparency based on graphene metasurface structure for mid-infrared sensing applications

The plasmon-induced transparency (PIT) effect in graphene metasurface (MS) structures is investigated through numerical and theoretical analysis in the mid-infrared range. The unit cell of the MS consists of two vertical and one horizontal graphene strip. By adjusting the Fermi energy, a blue shift in the PIT window occurs, while changes in the surrounding medium's refractive index cause a red shift, enabling tunable PIT control without altering the structure. Theoretical models using coupled Lorentz oscillators show good agreement with the simulation results, revealing a slow-light effect through increased group delay. Sensitivity, Q-factor, and figure of merit (FOM) show that sensitivity ranges from 7.0 to 11 THz/RIU as the refractive index changes, and FOM reaches around 180 with stable Q-factor at 15. This work provides a physical understanding of the tunable PIT effect in graphene MS structures and suggests potential applications in sensing, selective filtering, and advanced refractive index-based detection.