A dual-band mid-infrared polarization-insensitive perfect absorber

We propose a dual-band mid-infrared polarization-insensitive perfect absorber utilizing a cross-shaped indium antimonide (InSb) metasurface. The absorber comprises a multilayer structure with an InSb cross-shaped thin film, dielectric layers (Si₃N₄ and Al₂O₃), and a titanium reflective substrate. Through finite-difference time-domain (FDTD) simulations, the optimized design achieves near-perfect absorption efficiencies of 99.3% and 99.8% at wavelengths of 4.91 μm and 5.94 μm, respectively, under normal incidence. Impedance matching theory and multipole decomposition reveal that the dual-band absorption is primarily contributed by electric dipole (ED) and magnetic dipole (MD) resonances. Crucially, the four-fold symmetry of the cross-shaped InSb layer ensures polarization insensitivity, with absorption spectra overlapping perfectly for transverse electric (TE) and transverse magnetic (TM) modes. Due to its simple design and ease of fabrication, the absorber can be widely applied in various fields, including infrared imaging, optical communication, gas detection, and thermal radiation control, offering new possibilities for the advancement of related technologies.