## 4 Result Analysis
Moreover, AlN material has a large dielectric constant compared to other metals and plays a vital role in absorptivity. Therefore, it also influences the high absorption in the near and mid-infrared bands. Correspondingly, in Figure 9e-h, the magnetic-field intensity also gradually increases along the wavelength, high intensity is seen in the horizontal of the MMA, and the magnetic-field intensity gradually moves to the outer ring from the inner ring. The electric- and magnetic-field distribution of TM polarization is also presented in Figure 10, which shows similar behavior at TE polarization, but in 90-degree rotation. Therefore, the high wideband absorption of the proposed Ni-AIN-Ni ultrathin concentered hexagonal ring structure MMA originates from the combination of coupled results of multiple plasmons, SPP and the material itself. Figure 6: Indication of phi and theta angle of incident EM wave on MMA. Figure 7: Absorption of different oblique incident angles (**a**) TE and (**b**) TM polarization. Figure 8: Absorption of different polarization incident angles (**a**) TE and (**b**) TM polarization. Figure 10: The electric field \(|\)E\(|\), (**a**) 380 nm, (**b**) 1440 nm, (**c**) 2000 nm and (**d**) 2500 nm. The magnetic field \(|\)H\(|\) distribution of TM polarization (**e**) 380 nm, (**f**) 1440 nm, (**g**) 2000 nm and (**h**) 2500 nm. Figure 9: The electric field \(|\)E\(|\), (**a**) 380 nm, (**b**) 1440 nm, (**c**) 2000 nm and (**d**) 2500 nm. The magnetic field \(|\)H\(|\) distribution of TE polarization (**e**) 380 nm, (**f**) 1440 nm, (**g**) 2000 nm and (**h**) 2500 nm. mainly confined on the top concentrated hexagonal ring-shaped resonator surface, leading to the electric resonance. Therefore, the absorption appears because of the electric resonance. The impedance matching method is one of the crucial parameters for understanding absorption behavior, where the impedance matching among the optimal absorber and the surrounding medium is vital. The proposed absorber's effective impedance (\(Z_{\lambda}\)) is calculated by Equation (2) [36], which shows the relation between S\({}_{11}\), S\({}_{21}\), and Z\({}_{\lambda}\). The  
Figure 11: Surface current distribution of TE polarization for four operating wavelengths (**a**) 380 nm, (**b**) 1440 nm, (**c**) 1980 nm, (**d**) 2500 nm, gradually. Figure 12: Surface current distribution of TM polarization for four operating wavelengths (**a**) 380 nm, (**b**) 1440 nm, (**c**) 1980 nm, (**d**) 2500 nm, gradually. real and imaginary part of \(Z_{\lambda}\) is denoted by Re(Z) and Im(Z) in Equation (3), respectively. Moreover, the spectral absorptance (\(\alpha_{\lambda}\)) of the absorber is expressed by Equation (4). \[Z_{\lambda}=\sqrt{\frac{\left(1+S_{11}\right)^{2}-S_{21}^{2}}{\left(1-S_{11} \right)^{2}-S_{21}^{2}}} \tag{2}\]  
Figure 5:0  
Figure 5:1  
According to Equation (4), when the absorber's normalized impedance matches with the free-space impedance (\(Z=Z_{\rm o}=\)1), the perfect absorption has been attained. In other words, the closer the imaginary part is to zero, and the closer the real part is to one, the higher the absorption of the MMA. The relative impedance for the proposed MMAs' TM and TE wave polarization is presented in Figure 5:2 There is no significant or small change between TM and TE polarization impedance due to the symmetricity of the MMA patch. The wavelength 380 nm to 2700 nm shows that the impedance of the optical absorber matches the surrounding impedance (free space). The designed absorber realized high absorption of around 99% in the visible region. The rest of the wavelength varies slightly but maintains over 90% absorption. The metamaterial property is also vital for understanding absorption behavior. The effective refractive index (\(\eta_{\rm r}\)) is calculated by Equation (5):  
Figure 5:3  
where k =2\(\pi\lambda/c\), c is the velocity of light, S\({}_{11}\) is the reflection coefficient, S\({}_{21}\) is the transmission coefficient, n is the integer number and d is the substrate thickness.