Graphene-based Metamaterial Absorber Research Articles

Graphene-Based Metamaterial Absorber with Perfect Multi-band Absorption

Graphene-Based Metamaterial Absorber with Perfect Multi-band Absorption

Design and investigation on polarization insensitive dual band graphene based tunable absorber for THz applications

In this communication, a metal-free graphene-based Absorber is designed and examined in the THz regime. The graphene layer is coated over the SiO2 substrate, while the silver layer is used on the other side of the substrate. The designed absorber works in two frequency bands i.e. 2.2–2.91 THz (11–14 μm) and 4.85–5.83 THz (51–62 μm), having more than 90% absorption. Peak absorption is obtained 2.55 THz and 5.05 THz with 97.78% and 99.71% absorption. With the help of circular sectoring, the designed absorber shows wide polarization and wide incident angle (up to 60°) insensitivity for both TE and TM modes. Change in chemical potential of graphene provides the tunable characteristics in the designed absorber. All these outcomes confirm that the designed metal-free graphene-based metamaterial absorber works efficiently in THz regime and can be used in different applications such as, sensing and imaging.

Graphene-based metamaterial absorber for refractive index sensing applications in terahertz band

A tunable triple-band absorption-based refractive index (RI) sensor with a combined graphene pattern in the terahertz (THz) band has been proposed in this paper. The proposed sensor has the potential to be used for biosensing applications. Graphene split-ring and patch resonators are combined and used as a metamaterial element. The combined array structures are used to localize the incident electromagnetic field. In the proposed absorber, using the surface plasmon resonance (SPR) phenomenon of graphene, three narrow absorption peaks arise at frequencies of 4.66 THz, 6.035 THz, and 8.72 THz with absorption efficiencies of 99.2 %, 99 %, and 89 %, respectively. The overall performance and the position of the resonance frequencies are adjustable using an external DC-bias voltage applied to the graphene. The RI sensor is based on detecting changes in the RI of the sample under test, has a maximum sensitivity, Q-factor, and figure-of-merit (FoM) of 1791 (GHz/RIU), 32.354 and 7.046 RIU−1, respectively. Therefore, according to the mentioned features, which are obtained based on numerical simulations, the designed sensor is a good choice for medical and biosensing applications.

Quad-band tunable graphene-based metamaterial absorber operating at THz frequencies

Quad-band tunable graphene-based metamaterial absorber operating at THz frequencies

A tunable hybrid graphene-metal metamaterial absorber for sensing in the THz regime

In this paper, a graphene-based metamaterial absorber is proposed and investigated numerically, in which the interaction between a split ring resonator (SRR) and graphene results in a high-Q absorption. To make a better understanding of the resonance mechanism, the electric and the magnetic fields, and the surface currents at the resonance frequency are investigated. In order to ease the analysis of the structure, an equivalent circuit model is introduced using the transmission line theory, and the accuracy of the proposed model is verified by the full-wave simulation. Finally, different aspects of the designed metamaterial are discussed as a potential label-free sensor for chemical and biomedical sensing. It is shown that by using this structure, a sensor with a sensitivity of 597 GHz/RIU can be achieved.

Tunable Terahertz Perfect-Absorbers With Dual Peak Based on Reverse Graphene Patch Metamaterials

In this paper, we proposed a tunable graphene-based metamaterial absorber (MA) at dual terahertz band to achieve perfect absorption. The electric field intensity distributions of demonstrated structure is illustrated to explain the origin of two absorption peaks. Simulation result shows the proposed MA owning polarization-insensitive property and wide incident angle tolerance. An inversion algorithm is used to extract the equivalent impedance and explore the physical mechanism of multiple-peak absorption. The equivalent impedance is explored through algorithm when the Fermi energy level alters, consequently the variation of resonant frequency of corresponding absorption peak is determined. Simultaneously, the resonant frequencies of absorption peaks can be adjusted by changing the geometric parameters of the graphene. Furthermore, we adapt the proposed structure into reversely designed pattern, achieving similar characteristic of dual-band absorption peaks and tunability. Thus, our work provides new insight and useful design guidance to various tunable multiple band terahertz metamaterial perfect-absorbers.

A perfect electrically tunable graphene-based metamaterial absorber

In this paper, a metamaterial absorber based on graphene is proposed, designed and simulated numerically using multilayer structures. Before describing our work, the performance response of a three-layer structure is studied concerning one cylinder as a unit cell. Then, by varying the chemical potential of graphene (Fermi level of graphene) by applying external potential, the center frequency of this absorber can be adjusted. We will prove that by increasing the number of cylinders as fundamental elements in the unit cell, the bandwidth is also adjustable. Also, the center frequency can be affected by changing the dimensions of fundamental elements. Considering the above-mentioned items, the structure is investigated through increasing the graphene layers in which the absorber’s frequency response is wider respected to previous structures and the center frequency is adjustable as a result of variations in the chemical potential of graphene layers. It is shown that the proposed perfect absorber’s central frequency shift through graphene’s voltage variation is about 0.15 THz which can be increased to 0.3 THz by changing radius. In some of the introduced absorbers, the maximum value of the absorption has reached over 95%. The most important advantage of the proposed structure, which is the main purpose of designing terahertz metamaterial absorbers, is its adjustable bandwidth and center frequency, and simple fabrication.

A tunable broadband graphene-based metamaterial absorber in the far-infrared region

This paper reports a new design of a broadband absorber composed of graphene, dielectric, and gold layers. The designed absorber has four absorbent modes close to each other, which results in the formation of broadband absorption. The relative bandwidth, a key parameter to assess the bandwidth improvement, shows a significant increase in the proposed design compared to similar structures published in recent years. The numerical results also reveal this metamaterial absorber can be used for applications in the far-infrared frequency range due to choosing optimized dimensions and the graphene Fermi level. Unlike other graphene-based metamaterials, which require complicated structures to be able to attain broadband absorption, the physical structure of the proposed design has a relatively simple fabrication process. For further investigations, the effect of split geometry on the absorption spectrum is studied. Also, the use of graphene in this metamaterial absorber provides dynamic adjustability through electrostatic doping in order to tune the amount of absorption. This characteristic has been studied by changing the graphene Fermi level. This feature can be widely used in electro-absorption switches and modulators.

Independently Tunable Multipurpose Absorber with Single Layer of Metal-Graphene Metamaterials

This paper reports an independently tunable graphene-based metamaterial absorber (GMA) designed by etching two cascaded resonators with dissimilar sizes in the unit cell. Two perfect absorption peaks were obtained at 6.94 and 10.68 μm with simple single-layer metal-graphene metamaterials; the peaks show absorption values higher than 99%. The mechanism of absorption was analyzed theoretically. The independent tunability of the metamaterial absorber (MA) was realized by varying the Fermi level of graphene under a set of resonators. Furthermore, multi-band and wide-band absorption were observed by the proposed structure upon increasing the number of resonators and resizing them in the unit cell. The obtained results demonstrate the multipurpose performance of this type of absorber and indicate its potential application in diverse applications, such as solar energy harvesting and thermal absorbing.

A wideband and polarization-insensitive graphene-based metamaterial absorber

The concept of a wideband and polarization-insensitive absorber based on graphene for terahertz (THz) applications is presented in this paper. To broaden the absorption bandwidth, we have combined two concentric rectangular rings with cross-shaped strips. These are located on a silicon substrate. The analysis of the proposed absorber is based on the impedance matching theory and finite difference time domain (FDTD) methods. The simulated results show that the proposed absorber has a wideband absorption. The obtained bandwidth for absorption coefficients of 0.9 and 0.7 are 16% and 20.3%, respectively over the range of 2.47–2.9 THz and 2.39–2.93 THz. The bandwidth and absorption performance of the absorber can be adjusted by the control of the conductivity of graphene by applying an external DC-bias voltage. Due to the symmetrical design of the structure, the presented absorber is polarization insensitive. Furthermore, due to having a cross-strip structure, the performance of the proposed absorber is insensitive to the angle of the radiant wave. Thus, the proposed absorber can be considered a suitable candidate for various THz applications.

A reconfigurable multi-band, multi-bias THz absorber

A configurable terahertz (THz) graphene-based metamaterial absorber is designed in this paper. Taking advantage of dual bias graphene ribbons and disks with a golden plate, the reconfigurable absorber achieves absorption over 90% in three frequency bands include 0.8–2.2 THz, 5.5–6.5 THz and 7.5–8.5 THz. The chemical potentials of graphene patterns are optimized using a genetic algorithm. As the chemical potentials vary in the range of 0-0.6 eV, the device adds absorption bands while maintaining the previous absorption in lower frequencies. The whole device includes dielectrics, golden plate, and dual bias graphene patterns are modeled via the circuit model approach to calculate referred input impedance. This impedance is investigated regarding chemical potential effects on perfect absorption while other physical parameters such as ribbons widths and disks radiuses are fixed. Finally, the obtained suggestions of the algorithm are exploited to simulate the device with both full-wave numerical simulations as the finite element method (CST) and circuit model approach (MATLAB). According to simulation results, numerical simulation verifies validity and accuracy of circuit modeling to describe proposed device behavior. Compared to previous works, the proposed device as a reconfigurable THz absorber can overcome the limitation of traditional absorbers due to the capability of an add frequency band in absorption response while exhibits great potentials in many practical applications.

Near-infrared absorption-induced switching effect via guided mode resonances in a graphene-based metamaterial.

Optical switches based on dielectric nanostructures are highly desired at present. To enhance the wavelength-selective light absorption, and achieve an absorption-induced switching effect, here we propose a graphene-based metamaterial absorber that consists of a dielectric grating, a graphene monolayer, and a photonic crystal. Numerical results reveal that the dual-band absorption with an ultranarrow spectrum of the system is enhanced greatly due to the critical coupling, which is enabled by the combined effects of guided mode resonances and photonic band gap. The quality factor of the absorber can achieve a high value (>500), which is basically consistent with the coupled mode theory. Slow light emerges within the absorption window. In addition, electrostatic gating of graphene in the proposed structure provides dynamic control of the absorption due to the change of the chemical potential of the graphene, resulting in an optional multichannel switching effect. Unlike other one-dimensional devices, these effects can be applied to another polarization without changing the structure parameters, and the quality factor is significantly enhanced (>1000). The tunable light absorption offered by the simple structure with an all-dielectric configuration will provide potential applications for graphene-based optoelectronic devices in the near-infrared range, such as narrowband selective filters, detectors, optical switches, modulators, slow optical devices, etc.

Design of a Tunable Ultra-Broadband Terahertz Absorber Based on Multiple Layers of Graphene Ribbons

We propose and numerically demonstrate an ultra-broadband graphene-based metamaterial absorber, which consists of multi-layer graphene/dielectric on the SiO2 layer supported by a metal substrate. The simulated result shows that the proposed absorber can achieve a near-perfect absorption above 90% with a bandwidth of 4.8 Thz. Owing to the flexible tunability of graphene sheet, the state of the absorber can be switched from on (absorption > 90%) to off (reflection > 90%) in the frequencies range of 3–7.8 Thz by controlling the Fermi energy of graphene. Moreover, the absorber is insensitive to the incident angles. The broadband absorption can be maintained over 90% up to 50°. Importantly, the design is scalable to develop broader tunable terahertz absorbers by adding more graphene layers which may have wide applications in imaging, sensors, photodetectors, and modulators.

Active graphene metamaterial absorber for terahertz absorption bandwidth, intensity and frequency control

A novel graphene-based metamaterial absorber with actively tunable bandwidth, intensity and frequency, working at the terahertz (THz) spectral region, was designed and numerically investigated in this paper. The actively controlled absorption characteristics in the graphene absorber were achieved by integrating two identical-sized graphene disc elements to construct a supercell, in which two elements of all unit cells were connected respectively by the electrical isolation graphene wires to form selectively electrostatic doping. The surface current distributions and the circuit model analysis were conducted to reveal the absorption mechanism and predict the tuning mechanism. Moreover, by selectively tuning two gate voltages to change the Fermi energy reconfiguration state of two graphene elements, the absorption bandwidth, intensity and frequency of the metamaterial absorber could be actively controlled. In addition, a striking switching contrast was obtained by switching the reconfiguration state of the two discs. Therefore, this work paves a pathway for the realization of actively controlled terahertz waves based on electrically reconfigured graphene metamaterials.

Far-infrared multi-resonant graphene-based metamaterial absorber

Recent developments in metamaterial designs have opened up the possibility of absorption in the terahertz frequency range. In this paper, a multi-resonant absorber is presented in which the resonance frequencies are theoretically organized by doping graphene ribbons with a ring-shaped gold on each ribbon per unit cell. This action allows the free electrons to flow on a piece of graphene surface to produce several absorption peaks in the far-infrared spectrum. Besides, in order to adjust the absorber to respond at different and wide frequency spectra, the absorption peaks can be managed by manipulating the gate voltage and dielectric thickness. This periodic structure also consists of a dielectric substrate of silicon dioxide and a metal slab at its back to ensure the zero transmission. Moreover, the equivalent circuit and transmission line model are derived based on the reflected fields and vector-fitting method to facilitate analysis of the proposed design and evaluation of the full-wave simulation results. At the end, the sensitivity of the absorption against oblique incidence is studied for both TE and TM polarizations.

Broadband tunable graphene-based metamaterial absorber

This paper proposes a graphene-based broadband tunable absorber with over 90% absorption and is polarization insensitive at mid-infrared frequencies. The proposed absorber consists of a periodic array of a dual electric LC (ELC) metamaterial unit fabricated on a multilayer structure composed of Au/BaF2/graphene materials from the bottom to the top. In the proposed structure, interaction between the dual ELC unit and the graphene sheet generates three close resonant frequencies, thus leading to a broadband absorption from 25.08THz to 39.56THz. By varying graphene’s chemical potential, wide absorption bandwidth can be flexibly tuned. Due to the approximate symmetry of the structure, the proposed absorber demonstrates polarization-insensitive and wide-angle characteristics. Simulation results demonstrate that the absorption efficiency of the proposed structure can be as high as more than 90% from 25.08 THz to 44.81THz with variation of the graphene’s chemical potential from 0.2eV to 0.8eV.