## 3 Results and Discussion  
### The result of the Structure Tuning  
The working principle of this reflective MPA can be understood as follows. When the electromagnetic wave illuminates the device, the SPP is excited on the top graphene layer and the redundant energy in the absorber was reflected by the bottom PEC mirror, resulting in strong magnetic resonance [44; 45; 46; 47]. It is known from the properties of SPP that the SPP excited by the MPA will change the direction of energy propagation, thereby achieving the loss of these energy at the surface without reflection. Earlier works [22; 25; 48; 49] showed that a local surface plasma mode or a gap plasma mode illuminated by incident light will be excited inside the graphene microstructure, resulting in a significant enhancement of light absorption. First, with the above theory and the Formula (3), we can know that by changing the Fermi level of graphene, we can change the response frequency of the graphene absorption structure, which will change the position of the absorption peak of the graphene absorption structure. We control the Fermi level by changing the voltage between the gates. The relationship of the gate-voltage and the Fermi level is shown in the Formulas (6) and (7). Utilizing this property, we tune the Fermi level of the GCTR. The results are shown in Figure 2.  
The Figure 2 depicts the simulated absorption spectrum of the absorber which the Graphene at the different Fermi levels. From the theory of adjustable conductivity, we finally give the approximate relationship between the SPP response frequency \(\omega\) (the frequency corresponding to the absorption peak) and the Fermi level \(E_{f}\) of graphene. It can be seen that under the control variables, without changing any structural parameters of the absorption structure, as the graphene Fermi level increases, the surface plasma response frequency increases. This is consistent with the absorption spectrum we obtained through FDTD simulation. When we adjusted the graphene three-ring Fermi level \(E_{f}\) from 0.7 eV to 1.0 eV, the peak of the absorption blue shift (the surface plasmon response frequency increase). As the Fermi level increases, we can draw a general conclusion that all the graphene absorbing structures appear as a blue shift. It is consistent with the conclusion of conductance regulation. Moreover, the absorptions of the absorption peaks are fluctuating between 61% to 98% (the second peak) with the changes of the Fermi level. As well as that, it is apparent that the Fermi level plays a significant role in the absorption and the frequency of the absorption peak. Cause to the indispensable role of the Fermi level, we have a new idea that we maintain the Fermi level of the two rings unchanged and change the Fermi level of the single graphene ring (SGR). In this way, we can achieve the adjustment of SGR and thus achieve higher continuous absorption efficiency of the absorption peak with a poor coupling effect. The results are shown in Figure 3.  
The Figure 3 depicts that SGR adjustment not only can change the response frequency of the Graphene but also can change the efficiency of the absorption peak which will tune the absorber without the structure reengineering. Afterwards, we can see that we increase a new perfect absorption by adjust the Fermi level of SGR. Using the theory of adjustable conductivity, we finally provide the approximate relationship between the surface plasmon response frequency \(\omega\) (the frequency corresponding to the absorption peak) and the Fermi level \(E_{f}\) of graphene. Using this relationship, we can adjust the Fermi level of the largest graphene ring from 1.0 eV to 0.7 eV, and we can find that the absorption peak has a red shift phenomenon, which is consistent with the tunable conductivity model. We also found that the regulation of a single Fermi level can achieve the intersection of two absorption peaks to produce the sum peak effect.