# Combined Mie Resonance Metasurface for Wideband Terahertz Absorber
## 2 Structure Design and Simulation
The absorption peaks 1, 2, and 3 at frequencies of 0.85 THz, 0.867 THz, and 0.883 THz are marked with green arrows and labels “P1”, “P2”, and “P3”, respectively. The absorption valley 1 and valley 2 at frequencies of 0.857 THz and 0.875 THz are marked with green arrows and labels “V1” and “V2”, respectively. In order to better analyze this phenomenon, we then simulated the traditional Mie resonance-based metasurface. The schematic diagram is shown in Figure 3a. The dielectric blocks were arranged evenly and periodically on the aluminum substrate, with constant periods of both \(p_{x}=p_{y}=\)40 \(\upmu\)m. Each unit cell contained a single dielectric square block, whose sizes were a = 33 \(\upmu\)m, \(t\) = 30 \(\upmu\)m. The simulation setup was the same as previously mentioned. Figure 3b exhibits the absorption (black curve), transmission (red curve), and reflection (blue curve) spectra of the Mie resonance-based metasurface absorber with a single dielectric resonator in the unit cell. We can see that there was a reflection dip lower than 0.1 and an absorption peak of about 0.9 at around 0.869 THz, and the transmission was zero. We also simulated the electric field (E-field) and magnetic field (H-field) distributions of the single dielectric resonator at the frequency of the absorption peak. Cross-sectional H-field distribution in the \(x\)-\(z\) plane is shown in Figure 3c, and the cross-sectional E-field distribution in the \(y\)-\(z\) plane is shown in Figure 3d. At the frequency of 0.869 THz, the H-field was almost linearly parallel to the \(x\)-axis, and the vortical E-field was obviously distributed inside the dielectric block. This showed that a magnetic resonance occurred in the dielectric resonator at this frequency, illustrating that the absorption of this metasurface was related to the magnetic resonance. As for our combined metasurface absorber, the electromagnetic field distribution at the frequencies of three absorption peaks (the frequencies of peaks 1, 2, 3 were 0.85 THz, 0.867 THz, and 0.883 THz, respectively); these are shown in Figure 4a-c. Each part of Figure 4 displays the cross-sectional magnetic field distribution in the \(x\)-\(z\) plane with \(y\) = 40 \(\upmu\)m, 0 \(\upmu\)m, \(-\)40 \(\upmu\)m and cross-sectional electric field distribution in the \(y\)-\(z\) plane with \(x\) = \(-\)40 \(\upmu\)m, 0 \(\upmu\)m, 40 \(\upmu\)m for our combined metasurface absorber at different frequencies. At the absorption peaks 1, 2, 3, there were magnetic resonances, which were the same as the phenomenon inside the single block existing inside the third, second, and first row of squares, respectively. The magnetic resonance occurring in a smaller block corresponded to an absorption peak with a higher frequency. We also simulated the electromagnetic field distribution  
Figure 3: (**a**) Schematic diagram. (**b**) Simulated absorption/transmission/reflection spectra of the traditional metasurface with a single dielectric resonator in each unit cell. (**c**) The cross-sectional electric field distribution in the \(y\)-\(z\) plane and (**d**) the cross-sectional magnetic field distribution in the \(x\)-\(z\) plane for the unit cell of the traditional metasurface with a single dielectric resonator in each unit cell. at the absorption dips between peaks 1 and 2 and peaks 2 and 3, as shown in Figure 5. We could observe that although there were linear magnetic field and vortical electric field inside the blocks, the phenomenon was different. In Figure 5a, it can be seen that the strongest H-field was located at the second row of blocks, while the third row of blocks had the strongest E-field. In Figure 5b, it can be seen that the strongest H-field in the first row corresponded to the strongest electric field in the second row. This phenomenon indicates that there was a strong coupling between blocks at these two frequencies.