A Perfect Absorber for Ultra-long-wave Infrared Based on a Cross-Shaped Resonator Structure

To satisfy the marking demand for microwave absorbing devices, we design an ultra-broadband nearly perfect absorber. The proposed absorber demonstrates absorption band from long to very long-wavelength ranges (15.7-37.9 mu m). An average absorption efficiency of 95.16% and a satisfactory absorption bandwidth of 19.2 mu m are achieved. The absorption with high absorptivity and large bandwidth is achieved through combined propagating surface plasmon (PSP) resonances in two directions and localized surface plasmon (LSP) resonances. By simulating and calculating the absorptivity, we demonstrate that the absorber possesses the properties of polarization independence and incident angle insensitivity. When the incident angle reaches 60 degrees, the device still maintains a high absorptivity. Finally, the manufacturing process is illustrated, using radio frequency sputtering with dual guns or an E-beam. Compared with other related microwave absorbers, the proposed absorber balances the contradiction between absorption bandwidth and average absorption. We have strong confidence that the absorber has tremendous applications in many areas, such as infrared thermal emitters, imaging, and photodetectors.