Ultra-broadband metamaterial absorber in long wavelength Infrared band based on resonant cavity modes

Abstract

A wavelength-selective, ultrathin, broadband infrared metal–insulator–metal (MIM) absorber with multi-sized Ti–Ge cubes is proposed. By flexibly combining different sizes of Ti–Ge cubes, stacking upward and reasonably filling the border, all the resulting 3 structures that we propose show an average absorptivity of at least 90% over a wide spectral range in the infra-red, extending from 6. 3μm to 14.8μm. The absorptivity is further increased up to 99% when considering narrower spectral ranges such as 7.96-8.34μm and 11.02-11.75μm wavebands, which is superior than the previous work in long wavelength infrared band based on the MIM structure. Those characteristics vary depending on the 3 designs considered and studied in this work: single-layer structure, double-layer structure and modified structure. The intrinsic strong energy dissipation caused by highly lossy metal Ti (here Titanium) and excited low-Q cavity modes are key factors contributing to such efficient broadband absorption. The polarization and angle insensitivity are demonstrated by analysing the absorption performance with oblique incidences for both transverse electric wave (TE) and transverse magnetic wave (TM). Moreover, flexible combinations of different resonators allow trade-offs between the absorption bandwidth and the absorbance, which makes the operating waveband of the metamaterial absorber adjustable through proper design. The proposed broadband absorbers have many potential applications, including microbolometers, thermal emitters, and plasmonic sensors.