Silicon nitride-based ultra-wideband ultra-long infrared metamaterial absorber with large angle and high absorption

Abstract

In the study of mid-infrared band long wavelength infrared (LWIR) has attracted the attention of domestic and foreign researchers due to its great role in medical diagnosis and detection. Broadband absorption is also a key index for metamaterial absorption applications. In this paper, a design of a highly absorbing, large-angle ultra-wideband ultra-long infrared metamaterial absorber based on a single-layer square Si3N4 cavity array and an intermediate layer of Si3N4 thin film, as well as metal Ti as the substrate, is proposed. The ultra-long infrared metamaterial absorber has polarization insensitivity under the condition of positive incidence. Numerical simulations show that the effective absorption bandwidth with more than 90% absorption is 11.12 μm in the band range of 7.65-18.77 μm, in which the average absorption reaches 96.54%. Diffraction and impedance matching induced strong absorption and wide bandwidth. We can adjust the absorption performance by changing the structural size of the absorber. In addition, our design has a very wide operating range of incidence angles, and the TM and TE modes maintain ultra-high average absorption levels under 0°-60° incidence angles, it is worth mentioning that the absorption of the absorber can reach 95.08% at an incident angle of 60°. The absorber design proposed in this paper has a simple structure, the material is easily available and inexpensive, and the fabrication process is very simple, which makes it suitable for infrared imaging, medical detection, and thermoselectronic devices.