Long-Wave Infrared Ultra-Broadband Perfect Absorber with Embedded Structure

For high absorption of long-wave infrared spectra, a long-wave infrared ultra-broadband perfect absorber is designed in light of the impedance matching theory by the finite-difference time-domain method in this paper. First, a metamaterial absorber with a metal-insulator-metal structure is analyzed, and the absorber has an average absorptivity of greater than 91% in the range of 7-14 mu m. Then, on the basis of the metal-insulator-metal structure, an ultra-broadband perfect absorber with an embedded structure is designed. It has almost perfect absorption characteristics in the range of 7-14 mu m with an average absorptivity of over 97.55 % and appears to be insensitive to polarization. Its average absorptivity remains over 90% (90.5 % in the transverse magnetic mode and 93.7 % in the transverse electric mode) when the incident angle is 50 degrees. The research results show that broadband perfect absorption is mainly caused by the combined action of multiple modes such as surface plasmon and the Fabry-Perot resonator. The proposed absorber, with excellent absorption in the range of infrared spectra, holds a promising application prospect in fields such as energy harvesting and infrared sensors.