Design of metamaterial perfect absorbers in the long-wave infrared region

We designed a narrow-band metamaterial absorber (NMA) and an ultra-broadband metamaterial perfect absorber (UMPA) based on the impedance matching theory. The narrow-band metamaterial absorber mainly consists of Si₃N₄ cylinders with Si₃N₄ and Ti substrates. Numerical analysis shows that the absorption peak of the NMA is about 99.9% and the absorption bandwidth with more than 90% absorption is about 4.8 μm (9.5-14.3 μm). To further extend the absorption bandwidth, an ultra-broadband absorber was designed by integrating a Ti hyperbolic rectangle into the Si₃N₄ cylinder of the NMA. Numerical analysis shows that the absorption bandwidth of the UMPA is up to 10 μm (7-17 μm) with an average absorption rate of 96.6%. The designed UMPA has polarization insensitive properties with wide-angle absorption characteristics, and the average absorption can reach 85% and 76% in transverse magnetic (TM) and transverse electric (TE) modes, respectively, at 60° oblique incidence. The high absorption and wide band are mainly dominated by localized surface plasmon resonance, Fabry-Perot resonance and inter-resonance interactions. The designed absorber achieves excellent absorption in the long infrared wavelength band, which has potential applications in energy absorption, infrared sensing and other fields.