# Combined Mie Resonance Metasurface for Wideband Terahertz Absorber
## 3 Further Investigation on Different Incident Angles and Polarization States  
Next, we explored the influence of the polarization state and the incident angle of incident light on the performance of our combined metasurface absorber. Figure 7a is the schematic diagram of the irradiation of incident polarized light. The three red arrows represent the \(x\)-axis, the \(y\)-axis, and the \(z\)-axis, while the two green arrows represent the polarization direction of the magnetic field and the direction of the incident light. \(\varphi\) is the angle between the polarization direction of the magnetic field and the \(x\)-axis, while \(\theta\) is the angle between the direction of the incident light and the opposite direction of the \(z\)-axis in the x-z plane. Figure 7b displays the absorption spectra at different polarization of normally incident light. When \(\varphi=0^{\circ}\), our combined metasurface absorber had the widest absorption bandwidth. However, as \(\varphi\) became larger, the absorption bandwidth of the wave absorber became narrower. The bandwidths at 80% absorption for the combined metasurface were 0.047, 0.045, 0.038, 0.022, and 0.018 THz when \(\varphi\) equaled \(0^{\circ}\), \(22.5^{\circ}45^{\circ}\), \(67.5^{\circ}\), \(90^{\circ}\), respectively. The appearance of this phenomenon may be related to the fact that this metasurface absorber is based on magnetic resonance. When the magnetic field was along the \(y\) direction (the direction in which the side lengths of the resonators increase jumpingly, for example, \(\mathrm{a_{1}-a_{4}-a_{7}}\)), the absorption bandwidth was reduced to 40%. Despite this, the narrowest absorption bandwidth of our combined metasurface absorber was still nearly twice that of a single resonator. This proves that our combined metasurface absorber can effectively broaden the absorption bandwidth regardless of the polarization of the incident light. Figure 7c shows the absorption spectra at different incident angle of the incident light when \(\varphi=0^{\circ}\). When the light was normally incident, the absorption effect was the best. As the incident light gradually became tilted, the absorption rate slightly decreased, while the absorption bandwidth was almost constant. Even when the light was incident at a \(45^{\circ}\) angle, the absorption rate could still reach more than 75%. This shows that our combined metasurface absorber can still work well within a certain range of oblique incident angles. Figure 7: (**a**) Schematic diagram and absorption spectra of our wideband metasurface absorber consisting of nine dielectric resonators with different side lengths in one unit cell, (**b**) at different polarization angle, and (**c**) at different incident angle of the incident light. We can see that in Figure 7b, there are two little absorption peaks around 0.91 THz and 0.923 THz. We simulated the electromagnetic field distributions at these two frequencies, as shown in Figures 8 and 9. In Figure 8, it can be seen that vortical E-fields were mainly distributed inside the dielectric blocks of a\({}_{2}\)-a\({}_{6}\), while the H-fields inside the blocks of a\({}_{1}\), a\({}_{7}\)-a\({}_{9}\) were almost linearly parallel to the \(y\) axis. In Figure 9, vortical E-fields were mainly distributed inside the dielectric blocks of a\({}_{1}\)-a\({}_{3}\), while the H-fields inside the blocks of a\({}_{4}\)-a\({}_{9}\) were almost linearly parallel to the \(y\)-axis. At these two frequencies, there was a common feature that the linearly magnetic fields in some blocks excited the vortical electric field in other blocks. If you look at these nine pieces as a whole, this phenomenon is somewhat similar to higher-order mode. This special mode--due to near-field coupling--leads to additional small absorption peaks.