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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 pattern...
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Citations
... Since at THz frequencies, the energies of the photons that hit the surface of the graphene material are lower than the Fermi energy of graphene, (ћω<E F ) it neglects the interband transmissions and is considered only its intraband transmissions as Eq. (1) [23,24]. ...
... In other words, if the input impedance (Zin) is approximately equal to the free space impedance (Z0 = 120πΩ), the device can achieve maximum absorption. Conversely, when the input impedance deviates significantly from 120πΩ, absorption is minimized, leading to increased total transmission and reflection [20][21][22][23]. ...
... As a result, of the dependence of graphene surface conductivity on chemical potential, it can be claimed that by changing the chemical potential, it is possible to change the values of R-L-C in the graphene patterns ECM. [22][23][24][25] ...
As a basic building block, the THz wave absorber has intense imaging, sensing, and nondestructive testing applications. There are several methods for tuning THz absorbers, including electricity modulation, light modulation, mechanical tuning, using phase change materials, liquid crystal, flexible materials, MEMS technology, and thermally tuning vanadium dioxide. The choice of tuning method depends on the specific application and the desired performance characteristics of the THz absorber. In this work, we report a theoretical description of mechanically tunable THz absorber based on overlapping periodic arrays of graphene nano‐disks. The basis of this work is based on the movement of a dielectric surface covered on both sides with graphene disks. This surface moves on a fixed plane while the distance between these two surfaces is free space. Also, the fixed surface consists of a relatively thick layer of gold at the bottom, dielectric on it, and graphene disk patterns on the dielectric. Now, by moving the movable surface in the horizontal direction, it is possible to adjust the amount of absorption in different frequencies of the terahertz (THz) band. Additionally, an equivalent RLC circuit model is developed and theoretical results match with simulated data. The proposed mechanically tunable THz absorber can be exploited in various emerging applications such as sensing due to its capability of covering all of the THz gap and beyond with multiple absorption peaks.
... = 1∕ and is the relaxation time. Moreover, G is the permittivity of graphene, expressed by Eq. (2) [21]: ...
... This goal can be achieved by changing the chemical potential of the graphene in Eq. (6) [21]: ...
... The secure ability to apply and change external stimulation in the shape of biasvoltage provides an opportunity for proposing wave radiation-based meta-sensors performing multiple functions. Also investigating reconfigurability and adjustability will raise control resolution over device reactions [17,18]. ...
... reducing total costs. Using nested graphene patterns lets the designer to manipulate layer impedance with more resolution and consequently, more possible responses are available [13][14][15]. ...
A two-layers, multi-band super absorber with the capability of being tuned is proposed in this paper. The idea behind the design is to realize periodic arrays of graphene disks via graphene ribbons with different lengths. Then circuit modeling is developed to be used alongside the impedance matching concept to achieve more than ten absorption peaks. The exploited spacer is a lossless polymer in the THz frequency range while the bottom of the device is occupied by a relatively thick golden plate. The developed circuit model description is verified by full-wave simulation. According to the simulation results, the proposed absorber shows more than ten peaks with absorption over 90%. The peak frequencies are interestingly able to be shifted via exploited single chemical potential variations. Additionally, deviations of absorber response against graphene electron relaxation time and device geometry are shown to be marginal which makes the presented meta-absorber, a reliable optical device.
... Meanwhile, generally precise conditions are displayed to portray the graphene layer. 8 Additionally, 9,10 displayed proficient circuit models for graphene nano-strips and graphene nano-disks, individually, which consider the impacts of physical parameters such as the geometry and electron unwinding time at the side the impacts of predisposition voltage have taken into account. Concurring to numerous past works, the exactness of the circuit demonstrate execution has been compared with numerical strategies, most of which report a really great attention with the slight blunder of the circuit demonstrate strategy versus numerical strategies. ...
Coating both sides of a dielectric spacer with graphene patterns, leads to a tunable meta surface which acts as a THz duplexer. Two separate channels, reflection and transmission are considered as outputs ports while the aim is to minimize absorption ration. The presented structure consists of periodic arrays of graphene patterns on both sides of silicon dioxide as substrate. Moreover, the patterns include disks and rings are biased differently compared to conventional patterns which makes it possible to achieve tunable behaviors versus external bias. utilizing equivalent circuit models (ECM) for graphene patterns and dielectric, the whole structure is modeled by passive RLC branches. According to the simulation outputs, the presented structure can transmit and reflect incident THz waves at desired frequencies in 0.1 THz to 30 THz which makes it an ideal candidate for manipulating THz waves in terms of transmission and reflection. The THz duplexer can transmit and reflect incident waves at 1–3.3 THz as wide‐band and 1.05 THz as narrow‐band operation. Such a tunable device is in great demand for indoor communications, security, less harmful medical imaging and space related researches.
... The biasing limitation is due to the fact that the Graphene is ultra-thin (one carbon atom thickness) and may break under large electric fields. Optimistically 0 eV to 1 eV is considered as a feasible range otherwise larger values may lead to chemical reaction [13][14][15][16]. Some works have tried to overcome this limitation by introducing multi-bias patterns which allows further modifications after fabrication. ...
... This process also can be considered in a pre-stage optimization to enhance whole response. But this work is inspired by [14] regarding geometrical values. So, input referred impedance of the device is a sole function of chemical potentials since geometrical parameters are fixed. ...
... In (14) definition 'gamma' is defined as (Zin − Z0)/(Zin + Z0), where Zin is the input impedance of the device and Z0 is the impedance of incident medium, being equal to 120π Ω, while f h and f l denote the high and low frequencies which specify the frequency band. Maximizing these equations means that used correspondence individuals have great potential to show perfect absorption. ...
A three layers graphene-based THz absorber composed of multi-bias graphene ribbons is presented. The structure is described using equivalent circuit model and design methodology is developed via impedance matching concept. Also, relatively heavy optimization is utilized to obtain two sets of chemical potential values. Two operational behaviors are expressed corresponding to each bias set. Leveraging both equivalent circuit representation and impedance matching concept, the proposed structure is able to show both narrow multi band and wide band absorption over 0.1 THz to 5 THz frequency range. The first mode of operation can perfectly absorb THz incident waves in 0.5 THz, 1.4 THz, 2.35 THz, 3.23 THz and 4.11 THz while the second mode of operation absorbs THz incident waves between 0.5 THz to 2.5 THz as wide band response. Additionally, to investigate device dependency against geometrical parameters, electron relaxation time, chemical potentials and incident angle, ample simulations are reported for both modes of operations. Achieving both multi band and wide band absorption via a unique structure, makes the proposed device an ideal candidate to be used in optical systems and sensors for medical imaging, indoor communications and security.
... Thermoplastic Olefin Polymer of Amorphous Structure (TOPAS) is used as dielectric. The corresponding refractive index for TOPAS is n TOPAS ¼ 1:53, while this polymer express negligible losses at THz fre-quencies [24]. Besides a relatively thick golden surface is placed at the bottom of the device to ensure banned transmission. ...
A multi-layer absorber using multi-bias arrays of graphene is proposed. The design methodology using the equivalent circuit model and matching concept is described. A heavy optimization process is performed to optimize bias values for different functionality. Leveraging, increased control parameters due to multi-bias scheme and simple circuit model representation, two operational modes are achieved as wide-band and multi-band absorption. The proposed absorber can perfectly absorb THz incident waves between 5.2 THz−6.3 THz in wide-band mode while shows perfect absorption response in 5.3 THz,7.5 THz, 8 THz, 8.5 THz, 9 THz,and 9.5 THzin multi-band operational mode. Besides, response dependency to layers thicknesses, electron relaxation time, chemical potentials, and incident angle are reported to express acceptable sensitivity of the device. Such a reconfigurable absorber is in demand for several applications, ranging from medical imaging to indoor communication.
