Ultra‐Broadband Mid‐Infrared Metamaterial Absorber Based on Cross‐Ring Coupled Cavities

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Abstract
We propose a novel ultra‐broadband mid‐infrared metamaterial absorber by employing the finite‐difference time‐domain (FDTD). The absorber achieves an average absorption rate of 98.18% because the bandwidth covers the range from 9.72 to 19.97 µm, which is 10.25 µm wide, with absorption reaching as high as 99.94% and 99.40% at the two resonant peaks, respectively. To understand the origin of such high efficiency in more detail, we observe that these effects are caused by a combination of localized surface plasmon resonance (LSPR), magnetic polaritons (MPs), and cascaded Fabry–Pérot cavity resonances. The synergistic interplay of these mechanisms produces the ultra‐broadband absorption response. Furthermore, the absorption spectra of the absorber remain nearly unchanged under both transverse electric (TE) mode and transverse magnetic (TM) mode polarizations, indicating good‐polarization insensitive performance; moreover, the absorber has good angle stability, maintaining its performance over an incident angle range of up to 60°.

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