# Electrically Tunable Perfect Terahertz Absorber Using Embedded Combine Graphene Layer
## 1 Introduction  
In recent years, terahertz electronic devices have been significantly developed by utilizing metamaterials properties, and many researchers are attracted to this field. Working on the metamaterial regime due to exotic features with an exceptional conductivity leads to the creation of great high-tech achievements [1, 2]. With the advent of the Surface Plasmon Resonance(SPR) phenomenon, the fabrication procedure of equipment based on terahertz technology is also revolutionized, especially manufacturing detectors and perfect absorbers [3, 4]. The various wide range of absorbers as polarization insensitive/dependent absorbers [5, 6], broad/narrowband absorbers [7, 8, 9], hyperbolic absorbers [10], plasmonic absorber [11, 12], and van der Waals (vdW) absorbers [13, 14] have been engineered from microwave [15], through terahertz [16], infrared [17], and also into the visible range [18]. Recently, perfect absorbers composed of graphene have demonstrated a satisfactory performance due to its extraordinary electrical properties, optical transparency, flexibility, high electric mobility, and controllable conductivity [19].  
Graphene is a 2D nanomaterial comprising one monolayer of carbon atoms organized in a honeycomb lattice [20, 21]. Within infrared and terahertz frequency range, the surfaceplasmon polariton properties of graphene make this potential to generate the sharp peaks in the broad spectral region undertaking interaction between the incident light and graphene configuration, which can design such as nanostripes, nanoribbons, nanodisks, rings, and L-shaped arrays [22]. On one aspect, the conductivity surface of graphene plays a crucial role in setting the plasmonic resonance in the absorption band. The electrostatic control of conductivity gives the potential to adjust peaks regarding plasmonic resonances in perfect absorbers and detectors constructed by graphene [23; 24; 25]. Graphene can function as a gate-voltage element whose optical features depend on chemical potentials that can be varied using an external voltage. On this basis, the optical response in the absorption band can be engineered through structures that are configured with graphene [26]. Recent studies illustrate a particular attraction in the design of absorbing devices based on a single graphene layer and investigations of design challenges in the near-infrared and visible ranges [27; 28]. For microwave range, the graphene layer is also interestingly used to design an optically tunable absorber [29] and switchable radar absorbing surfaces [30]. One of the most straightforward configurations that can be utilized to design a tunable terahertz absorber is combine architecture. Such structures have already been used to design radiofrequency filters for wireless and mobile applications based on advantages as small size, low cost of its fabrication, and high-quality factor [31; 32].  
This article proposes a unique absorber structure composed of graphene combine layers and a stripline with a particular metal and insulator configuration, which can be tuned independently by an external voltage bias. The results regarding the suggested structure are established via highly numerical simulations in CST Microwave Studio. Shifting the resonant peak of the presented absorber is demonstrated by applying voltage bias as the Fermi level of graphene changes. Moreover, the effect of the size variation of the graphene layers on the current configuration is evaluated. The electric field distribution on the conductivity surface of graphene is to be revealed by finding a better understanding of the involved physical mechanisms.