# Electrically Tunable Perfect Terahertz Absorber Using Embedded Combine Graphene Layer
## 4 Simulation Results  
First, the proposed absorber is implemented via the dimensions as mentioned above. A plane wave as an incident wave with the intensity of 1 \({}^{\mathrm{v}}\)/\({}_{\mathrm{m}}\) shines to structure from the top, whereas the incidence vector is aligned with the normal vector of the combline conductive surface of graphene. The transmission parameter concerning the proposed structure is negligible due to the thickness of the gold substrate and its high refractive properties; hence absorption and reflection factors count as the key parameters to affect the optical characterizations of configuration. In addition, the initial Fermi energies considered for graphene layers are \(E_{f}\) = 0.43 eV for the nanostripe line, \(E_{f}\) = 0.7 eV for combline configuration. These Fermi levels can be provided by applying DC bias voltage separately to each graphene layer available in the absorber configuration. Based on the initial geometry of the modeled absorber, Absorption Cross-Section (ACS) of the structure is computed numerically in the considered absorption band, as demonstrated in Figure 2. The simulated result shows that the proposed absorber's absorption peak happens on 11.348 THz in the absorption band with an absorption rate of 2.366 \(\times\) 10\({}^{5}\) nm\({}^{2}\). Electromagnetic field distributions of the developed model for transverse electric (TE) and transverse magnetic (TM) modes in absorption peak indicate that the combline graphene layer of the model plays \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Parameter** & **p (nm)** & **s (nm)** & **d (nm)** & **t (nm)** & **G (nm)** & **L (nm)** & **W (nm)** \\ \hline Size value & 7.5 & 10 & 25 & 6.25 & 25 & 400 & 400 \\ \hline \end{tabular}
\end{table} 
Table 1: Initial geometries of the combline graphene layer embedded for perfect absorber. Figure 1: Schematic diagram of terahertz graphene absorber. (**a**) 3D structure. (**b**) From the top view. the leading role in the creation of an absorption peak and stimulate plasmon polaritons, and the coupling effect on the nano stripline is trivial, as shown in Figure 3. This means that electron density on the nano stripline in this state is minor due to the small width of the graphene stripline. In the following, this can be outlined that manipulating the Fermi level in the combine layer can shift absorption peak in the spectral characterization, and TE mode plays a predominant role in the radiation profile of the proposed structure. In detail, the electron concentration over the combine sheet embedded between two insulators under interaction with incident light provides a powerful plasmonic scattering that maximum value of the electric field can be seen in the gap between combine's ribbons. As a theoretical point, TE and TM modes are introduced as indicators for polarization inside a device in which only electric field for TE mode and magnetic field only for TM mode are considered along the direction of propagation. Figure 2: (**a**) the implemented configuration of THz combine perfect absorber, (**b**) Absorption Cross Section (ACS) of the proposed absorber. To explore the concept with the change effect of geometric specifications of the combline graphene layer on spectral characterization of the absorber is investigated by focusing on the size and number of nanoribbons and the distance between them from each other. In the first step, the ribbon width of the combline graphene layer is manipulated. On this basis, the variation of the initial parameters of the ribbon layer is categorized as Table 2. It is clear that absorption characteristics of the proposed absorber change under the impact of size variation of combline graphene layer because the surface plasmon on this layer has a decisive role in determining absorbance rate. With this in coordination, simulation results in Figure 4 also indicate variations of absorption parameters as depicted earlier. Table 3 shows the changes in absorption parameter numerically.