A multifunctional bidirectional metamaterial perfect absorber for efficient narrowband and broadband absorption

In this study, we introduce a bidirectional metamaterial perfect absorber capable of achieving both four narrowband and broadband absorption. Unlike conventional single-band metamaterial perfect absorbers, our proposed design enables switching between four distinct narrowband and broadband absorption modes. The absorber consists of several layers of planar structures, with the top layer featuring a grating structure. When illuminated from above, the absorber exhibits four absorption peaks at wavelengths of 575.7 nm, 625.1 nm, 929.5 nm, and 1667.4 nm, corresponding to absorption rates of 99.66 %, 99.82 %, 99.85 %, and 92.21 %, respectively. We validate our design through finite-difference time-domain (FDTD) simulations and coupled mode theory (CMT) fitting, finding excellent agreement between the two methods. The observed narrowband perfect absorption arises from the synergistic effects of local surface plasmon resonance (LSPR), gap resonance, and Fabry-Perot (F–P) cavity resonance. Furthermore, our analysis reveals that the structural sensitivity is notably high. Employing the CIE (International Photometric Commission) color model, we convert the reflected spectra in the visible range into color estimation values, thereby enhancing the aesthetic appeal of the structure. We observe that varying the grating thickness results in a spectrum of rich colors. Notably, when electromagnetic waves are incident from the back of the device, it demonstrates an exceptionally wide absorption bandwidth of 1634.2 nm, with an average absorption rate of 98.54 %. Electromagnetic field analysis attributes this efficient broadband absorption to F–P cavity resonance. Remarkably, within a certain manufacturing tolerance range, the absorber retains its broadband absorption characteristics. Under the AM 1.5 solar radiation spectrum, the energy absorption rate reaches 95.98 %, while at a temperature of 1800 K, the absorber exhibits a high thermal emissivity of 98.67 %. Additionally, the narrowband absorption is polarization-dependent, whereas the broadband absorption is polarization-independent. Given these attributes, the proposed bidirectional absorber holds significant promise for applications in sensing, detection, photovoltaic power generation, and solar thermal energy conversion.