# Electrically Tunable Perfect Terahertz Absorber Using Embedded Combine Graphene Layer
## 4 Simulation Results
In the continuation of this work, the width of the upper layer of graphene is changed from 25 nm to 5 nm, 65 nm, 100 nm, 140 nm to evaluate the impact of the graphene stripline existence on the absorption peak. The electric field distribution of structure in Figure 3 indicates the weak couplings of stripline; however, widening the stripline can influence the absorption characterization by providing a good scattering effective area and altering the scattering profile of the structure. In other words, an increase in nano-stripline width leads to creating a broader surface with the potential for more electron concentration; consequently, interaction incident light with graphene stripline manipulates localized surface plasmon of graphene, which shifts plasmonic resonance upon absorption band. In addition, an enhancing trend happens, which is due to increased electron density. Figure 4b and Table 4 demonstrate the simulation results related to the manipulations as mentioned above. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Geometric Specification** & **s (nm)** & **t (nm)** & **p (nm)** \\ \hline Variation.I & 8 & 8.25 & 9.5 \\ Variation.II & 12 & 4.5 & 7.5 \\ Variation.III & 6 & 10.25 & 11.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Manipulation of size parameters on the combline graphene layer. Figure 3: Electromagnetic field distribution for TE and TM modes in the peak of absorption. \begin{table}
\begin{tabular}{c c c} \hline \hline
**The Width of Graphene** & **Plasmonic Resonant** & **Absorption Intensity (\(\times 10^{5}\)** \\
**Stripline (nm)** & **Frequency (THz)** & **nm\({}^{2}\)**)** \\ \hline
5 & 11.386 & 2.299 \\
25 & 11.346 & 2.366 \\
65 & 11.2 & 2.4 \\
100 & 11.052 & 2.521 \\
140 & 10.92 & 2.704 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Variations of absorption characteristics due to stripline’s width manipulations. Figure 4: (a)The influence of geometric variation of ribbons on ACS of the perfect absorber, (b) the effect of changing in the width of graphene stripline layer on ACS of the absorber. In general, it can be understood from the results in Figure 4a,b, and Tables 3 and 4, the resonant frequency and absorption peak on the spectral response of the structure are shifted by changing the size of ribbons. In further detail, manipulating the ribbon area causes the effective permittivity of configuration to vary due to change in effective area for electron concentstion [42; 43]. Thus, the plasmon mode of the structure changes, and a new electromagnetic field profile is generated. Accordingly, the proposed model's absorption amplitude and resonant frequency are altered in each term of variations; that is why absorption intensity goes up and down due to the constructive and destructive effects of the scattering profile. The impact of stripline width (str.w) change on the absorption spectrum appears a redshift on the absorption band. An increase in absorption amplitude in both size variations because of enlarging the effective conductive area was observed. Then, we focus on the number of available teeth of the combine graphene layer, considering 23 on each side of the initial design. To understand the effect of combline's teeth, the number of ribbons is first decreased to 17 on each side while the dimensions of the ribbons are fixed (s = 10 nm). In this state, the initial geometries of the combline configuration are turned into t = 12.25 nm and p = 9 nm. The simulated results in Figure 5 and Table 5 demonstrate, a redshift happens on the absorption band. Also, the absorption amplitude experiences a lower intensity rather than the absorption value of the initial architecture. Next, the teeth number of the graphene layer of the configuration is increased to 26 ribbons on each side. On this basis, the original specifications of the graphene layer are converted to t = 4.25 nm, p = 8.75 nm. An increase in the number of ribbon teeth enhances the absorption amplitude in addition to blueshift.