The realization of broadband absorption in the terahertz spectra is of significant interest in advanced terahertz applications. In this work, a novel ultrabroadband absorber based on the periodic array of graphene disks and graphene continues sheet is proposed. A developed transmission line theory besides the analytical circuit model of graphene disks and graphene continues sheet are exploited to describe the absorber structure by its circuit model. By using three graphene layers and considering impedance matching concept, the normalized bandwidth of 90% absorption is extended up to 121% of the central frequency. Also, the dependence of the absorption spectra on the structure parameters is investigated and analyzed. Moreover, the performance of the device under possible fabrication errors is discussed. In pursuit of evaluating the efficiency, accuracy, and validity of the proposed method, full-wave numerical modeling is performed by the finite element method. The results show that the proposed circuit approach, in addition to having advantages in terms of computing time and the need for memory resource, is in a good agreement with the full-wave simulations. Furthermore, the structure of the absorber is relatively simple, and it can be manufactured by chemical vapor deposition techniques.
Utilizing a double bias scheme for graphene patterns as a single layer, a THz meta-surface structure is proposed. The structure includes two dual bias layers and a graphene continuous sheet on top. So five possible biases are available which lead to a highly tunable absorption response. All consisting parts are modeled via passive circuit elements to obtain whole device input impedance. Then impedance matching theory is used to investigate potential frequencies for perfect absorption. Also, ample simulations are performed to show the validity and accuracy of theoretical descriptions. According to the simulation results in the conventional finite element method as a reference approach is in acceptable agreement with the developed circuit model approach. The proposed structure shows nearly perfect absorption in 5, 6, 7, and 8 THz with absorption rate over 90%. Such a tunable reaction is in incredible requests in optical systems and has various applications in structuring sensors, modulators, and photonic functions.
Electrical control of terahertz (THz) radiation for high‐performance THz imaging is the key point. The spectrum suffers from a lack of active and available materials such as graphene have a severely limited bias range leading to restricted tuning. Therefore, here we demonstrated an efficient tunable device exploiting a triple bias layer for patterned graphene ribbons. Here, the patterned graphene acts as a tunable surface impedance leads to electrically controlled impedance matching between the device and free space. So, a dual‐band absorption is obtained which is appropriately robust against incident angle and capable of adjusting absorption peaks. The major contribution of the design is capability of manipulating patterns periods via gate biasing. This causes providing additional degree of freedom compared to conventional graphene patterns. According to the simulation results, the proposed device shows excellent tuning operation via gate bias voltages.
Purpose
A wide band perfect THz absorber is presented in this work. The structure includes two layers of graphene disks on the silicon dioxide dielectric layer while a golden plate is placed at the bottom to act as a fully reflecting mirror against THz waves. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time. The designed THz absorber in this work is an appropriate basic block for several applications in THz optical systems such as sensors, detectors and modulators.
Design/methodology/approach
The layers in the proposed device are modeled via passive circuit elements and consequently, the equivalent circuit of the device is calculated. Leveraging the developed equivalent circuit model (ECM) and impedance matching concept, the proposed device is designed to perfect absorption with 4.7 THz bandwidth that possesses over 90% absorption. Ample simulations are performed using MATLAB (ECM) and CST (finite element method) to verify the superior performance of the device. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time.
Findings
This work reports a wideband THz absorber, composed of two graphene layers. This paper considers the circuit model representation for two different layers of the device. For a unique structure, a highly tunable response versus chemical potential is obtained. The circuit model approach and impedance matching theory are exploited to reduce computational time regarding conventional approaches.
Originality/value
A wide band absorber in THz band is presented. Leveraging circuit model approach and impedance matching theory, the design procedure is simplified regarding CPU time and memory requirements compared to conventional methods. Detailed calculations and ample simulations verify the performance excellency of the device to absorb THz incident waves in 2–6.5 THz frequencies. Also, the robustness of the device is investigated versus parameters mismatches like layers thicknesses and chemical potentials values. According to the simulations and absorption response, the proposed device is an appropriate block to be used in THz optical systems such as detectors, imaging systems and optical modulators.
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