Broadband long-wave infrared metamaterial based on square-patterned Cr-based multilayer absorber

A four-layer planar metamaterial absorber with a Cr–SiO 2 –Si 3 N 4 –Ti stack is presented, featuring a square-patterned top Cr layer, intermediate SiO 2 and Si 3 N 4 dielectric layers, and a bottom Ti substrate. Numerical simulations are performed using the Finite-Difference Time-Domain (FDTD) method. The absorber achieves an absorptivity exceeding 90% in the 8.58–16.20[Formula: see text][Formula: see text]m band, with an average absorptivity of 96.9% and three absorption peaks at 8.86[Formula: see text][Formula: see text]m (99.9%), 9.65[Formula: see text][Formula: see text]m (99.9%), and 14.96[Formula: see text][Formula: see text]m (99.5%). It exhibits polarization insensitivity at normal incidence (0–90 ∘ ) and maintains high absorptivity up to 50 ∘ oblique incidence for both TE and TM polarizations. The broadband high absorptivity originates from the synergistic coupling of Localized Surface Plasmon Resonance (LSPR), Fabry–Pérot (F–P) cavity resonance, and Surface Plasmon Polaritons (SPPs).