Dynamically tunable and polarization-insensitive dual-band terahertz metamaterial absorber based on TiNi shape memory alloy films

Abstract A crucial point of restricting its development and application is the lack of dynamically tunable devices in the terahertz fields. In this work, shape memory alloys (SMAs) are innovatively introduced into the design of THz metamaterials absorber (MMA). An optimized structure design is proposed, and the MMA exhibits the perfect properties of dynamical tuning, polarization insensitivity, and dual-band absorption. In detail, two discrete resonance peaks can be detected, and their corresponding absorbance is up to 98.8% at 0.9982 THz and 96.8% at 1.5328 THz, respectively. The effect of structural parameters on the absorption performance is investigated further to reveal these two peaks' formation mechanism. Based on the martensitic transformation of TiNi alloy, the absorption peaks can be dynamically tuned to the desired operating frequencies through varying the external thermal field. Meanwhile, the absorber is polarization-insensitive when it is incident vertically due to the symmetry of the structure, and the excellent absorption performance can be maintained over a wide angular range of incidence. On account of the ultra-narrow bandwidth and the high-quality factor Q, we discuss the sensing ability of peak B. It can be found that peak B is sensitive to a minor change of the refractive index n of surrounding media and shows sensing ability. Through theoretical analysis, the sensitivity of the sensor is up to 0.88 THz/RIU, and the sensor’s figure of merit can be up to 92.63. This work proposes a novel idea of the design of various SMAs-based dynamically tunable terahertz optical devices.