Terahertz Absorber Research Articles

Graphene Multi-Frequency Broadband and Ultra-Broadband Terahertz Absorber Based on Surface Plasmon Resonance

When surface plasmon resonance (SPR) occurs, the incident light is absorbed by the surface of the SPR structure, thus minimizing the intensity of the reflected light. Therefore, the SPR method is adopted in this paper to achieve perfect absorption of the absorbent. In this paper, we first propose a multi-frequency broadband absorber structure based on graphene SPR, which uses the continuous resonance of patterned graphene surface plasmon in the frequency spectrum to form a multi-frequency broadband absorption. In this simulation, a sandwich-stack structure was adopted, whereby the patterned graphene is situated on top of the SiO2 layer and the metal layer. The broad-band absorption bands of the absorber were obtained as 4.14–4.38 THz, 5.78–6.36 THz, and 7.87–8.66 THz through the analog simulation of finite-difference time-domain method (FDTD) solutions. Then, based on the multi-layer resonant unit structure, through the superposition and combination of absorbing units responding to different frequency bands, the perfect absorption of ultra-wideband is achieved. The data results illustrate that the total absorption bandwidth of the absorber is 2.26 THz, and the relative absorption bandwidth Bw is equal to 28.93%. The electric field in X-Y direction of the absorber in the perfect absorption band is analyzed, respectively, and the dynamic tunability of the absorber is studied. Finally, we studied whether the absorbing structure still has efficient absorption characteristics for the two polarization modes when the incident angle is changed from 0° to 70°. The structure model proposed has potential value for application in terahertz photoelectric detection, filtering, and electromagnetic shielding.

Conducting fillers based multilayer polymer composites for terahertz absorber applications

Conducting fillers based multilayer polymer composites for terahertz absorber applications

Ultra-broadband polarisation-insensitive far infrared absorber based on an umbrella tungsten array structure

The technical study of metamaterial broadband perfect absorbers is gradually gaining widespread attention in the ongoing research. Due to its different aspects such as high absorption, frequency selectivity and ease of design, its application in various fields is showing more and more possibilities and prospects. In this research project, we propose an ultrabroadband, polarisation-insensitive​ metamaterial terahertz absorber based on an umbrella absorption cell that can be used as a far-infrared absorber, which uses tungsten (W) refractory metal as the absorber layer. From the results of our simulations, we can see that the absorber can achieve an absorption bandwidth of 3.3–15 THz, and the average absorption of the absorber can reach more than 99.0%. The absorber has a large absorbance in the far-infrared band and can be considered as a far-infrared absorber.

A Tunable Terahertz Absorber Based on Double-Layer Patterned Graphene Metamaterials.

Graphene is widely used in tunable photonic devices due to its numerous exotic and exceptional properties that are not found in conventional materials, such as high electron mobility, ultra-thin width, ease of integration and good tunability. In this paper, we propose a terahertz metamaterial absorber that is based on patterned graphene, which consists of stacked graphene disk layers, open ring graphene pattern layers and metal bottom layers, all separated by insulating dielectric layers. Simulation results showed that the designed absorber achieved almost perfect broadband absorption at 0.53-1.50 THz and exhibited polarization-insensitive and angle-insensitive characteristics. In addition, the absorption characteristics of the absorber can be adjusted by changing the Fermi energy of graphene and the geometrical parameters of the structure. The above results indicate that the designed absorber can be applied to photodetectors, photosensors and optoelectronic devices.

A Novel Triple-Band Terahertz Metamaterial Absorber Using a Stacked Structure of MoS2 and Graphene

A MoS2 and graphene stacked structure is proposed as metamaterials for a triple-band terahertz absorber in this work. The complementary frequency-selective surface of the absorber, consisting of two crossed linear slots and four pairs of concentric circular slots, has three absorptions at 0.6 THz (99.7%), 1.5 THz (95.4%), and 2.5 THz (99.5%). The polarization of the THz absorber is less sensitive to the incident angle within a certain range. By controlling the material properties of MoS2 and graphene, the peak absorption frequency can be tuned within a certain range. The stacked structure of different 2D materials provides new ideas for the design of the THz absorber, which is important for THz in detection, communication, and imaging applications.

A Voltage-Tuned Terahertz Absorber Based on MoS2/Graphene Nanoribbon Structure.

Terahertz frequency has promising applications in communication, security scanning, medical imaging, and industry. THz absorbers are one of the required components for future THz applications. However, nowadays, obtaining a high absorption, simple structure, and ultrathin absorber is a challenge. In this work, we present a thin THz absorber that can be easily tuned through the whole THz range (0.1-10 THz) by applying a low gate voltage (<1 V). The structure is based on cheap and abundant materials (MoS2/graphene). Nanoribbons of MoS2/graphene heterostructure are laid over a SiO2 substrate with an applied vertical gate voltage. The computational model shows that we can achieve an absorptance of approximately 50% of the incident light. The absorptance frequency can be tuned through varying the structure and the substrate dimensions, where the nanoribbon width can be varied approximately from 90 nm to 300 nm, while still covering the whole THz range. The structure performance is not affected by high temperatures (500 K and above), so it is thermally stable. The proposed structure represents a low-voltage, easily tunable, low-cost, and small-size THz absorber that can be used in imaging and detection. It is an alternative to expensive THz metamaterial-based absorbers.

Switchable dual-broadband to single-broadband terahertz absorber based on hybrid graphene and vanadium dioxide metamaterials

Switchable and tunable broadband perfect absorbers have drawn great interest in a wide range of applications, including modulation, energy harvesting, and spectroscopy. Here, we propose a switchable and tunable terahertz (THz) metamaterial absorber with dual-broadband, single-broadband perfect absorption using graphene and vanadium dioxide (VO2). Simulation results show that, when VO2 is in the insulated state, this design behaves as a dual-broadband absorber with over 90% absorption in 0.73 THz–1.53 THz and 3.03 THz–3.64 THz under normal incidence. When VO2 is in the metallic state and the graphene Fermi energy is set as 0.01 eV, this design acts as a single-broadband absorber with over 90% absorption in 1.00 THz–3.55 THz and the fractional bandwidth reaches 112%, which is much larger than the previously reported values. The absorption rate can be dynamically tuned by individually changing the conductivity of VO2 and the Fermi energy of graphene. Moreover, this design exhibits polarization-insensitive and wide-incident-angle behaviors for both TE and TM waves. Such a design may have potential applications in many fields, such as thermal detectors, modulators, and stealth technology.

A tunable broadband polarization-independent metamaterial terahertz absorber based on VO2 and Dirac semimetal

A broadband tunable metamaterial absorber with polarization and angle-insensitiveness is proposed for terahertz frequencies. The metamaterial design consists of a dielectric layer separating a periodic array of wheel-shaped vanadium dioxide (VO2) inclusions and a Dirac semimetal (DS) backplane. Numerical simulations show that the absorption performance can be flexibly adjusted from 4.3% to nearly 100% by changing the conductivity of VO2, the Fermi energy of DS, the permittivity of the dielectric spacer and the structure’s parameters. A 5.37 THz ultra-wideband absorptance over 90% can be achieved from 4.04 THz to 9.41 THz when the permittivity of the dielectric is 1.34 under normal incidence. The impedance matching theory, the Fabry–Pérot interference, and the electric field distributions are introduced to discuss the physical mechanisms of the broadband absorption. The upper edge of the absorption band is sensitive to the refractive index of the analyte, and a high sensitivity of 1.94 THz/RIU has been obtained around 4.5 THz. The proposed absorber possesses the advantages of polarization-independence and wide-angle tolerance both for TE and TM waves. The terahertz tunable broadband absorber has potential applications in terahertz energy harvesting, sensing, and modulation.

Thermally switchable terahertz absorber based on a VO2-included one-dimensional photonic crystal

Thermally switchable terahertz absorber based on a VO2-included one-dimensional photonic crystal

Triple band terahertz metamaterial absorber within (0.4-0.46thz) frequency range

An ultrathin Terahertz Triple-band ideal meta material absorber with a brand-new design that is straightforward has been presented. The suggested terahertz meta material absorber has a unit cell that is made up of two D-shaped resonators with slots and a ground metallic plane. These elements are separated from one another by a polyimide dielectric substrate that has a thickness of 500 micrometers. The absorber construction that has been presented provides three distinct absorption peaks within the narrow frequency range of (0.4-0.46 THz) without producing any interference. In order to get a deeper comprehension of the mechanism behind the absorption process, an investigation into the electric field, the magnetic field, the surface current distribution, and the independence of the polarization angle has been carried out. It is anticipated that the configuration of the terahertz absorber that has been described would find use in applications relating to the lowering of radar cross-section, detection, imaging, and sensing. One of the contributions of this study is the description of a downsized and compact triple-band terahertz meta material absorber. In order to generate the unit cell of a terahertz absorber, an identical I-typed resonator, which is represented by a rectangular patch with two very small notches, is first deposited on top of a dielectric sheet and then a metallic mirror. The terahertz regime reveals three distinct frequency spots, and the design of the very small structure allows for virtually full absorption of all of them.

Ultra-broadband tunable terahertz absorber based on graphene metasurface with multi-square rings

In recent years, thinness, lightness, broadband, high absorption, and tunability have become five important elements for electromagnetic (EM) absorbers. This article proposes a novel single-layered graphene metasurface absorber (GMSA) that perfectly achieves all of the above elements. The GMSA differs from common hybrid patterns in that it adopts a graphene layer with a simple multi-square ring structure. The simulation results show that Fabry-Perot resonance (FPR) and graphene-based surface plasmon resonance (GSPR) can be combined to produce the broadband absorption of 3.04 THz in the terahertz (THz) frequency range. The proposed GMSA is completely polarization-insensitive because of its symmetrical configuration, and it exhibits wide-angle oblique incidence properties for both TE and TM-polarized waves, allowing it to achieve broadband absorption with at least 90% absorption in the range of incident angles from 0° to 45°. In addition, the chemical potential of graphene can be altered to change the effective absorption bandwidth, which can be easily tuned by the applied external voltage. The GMSA has broad application prospects in THz detection, imaging, and object cloaking due to its flexible and straightforward construction, polarization insensitive, wide-angle incident, broadband, and high absorption qualities.

Carbon nanotube-based electrically tunable broadband terahertz absorbers

Terahertz (THz) absorbers are vital for confining electromagnetic waves in a wide range of light-matter applications. The actively tunable elements for improving the operation bandwidth limitations and the polarization features of absorbers are essential indexes for evaluating their performance. Therefore, THz absorbers with active functionality, polarization sensitivity, and straightforward fabrication are in high demand. Here, we present carbon nanotube (CNT)-based electrically tunable THz absorbers in an asymmetric Fabry‒Perot cavity. The self-assembled CNTs provide active electrical tunability as well as polarization selectivity. The experimental results show that absorbers composed of continuous and unstructured films exhibit almost perfect absorbance up to 99% from 0.2 THz to 1.6 THz. The absorbance of broadband absorbers is tuned from 48% to 99% at 1.6 THz, and the modulation depth (MD) is as high as 52%. The proposed electrically tunable absorbers with a straightforward fabrication method outperform most absorbers; these proposed absorbers promote THz applications such as filtering, biosensing, optical switching, polarized imaging, and telecommunication.

Ultra-broadband shielding of cellulose nanofiber commingled biocarbon functional constructs: A paradigm shift towards sustainable terahertz absorbers

Terahertz (THz) spectrum and technology are envisioned to be a highly promising solution for enabling 6G and beyond wireless networks. This demand coincides with an urgent need to develop efficient electromagnetic interference shields to alleviate electromagnetic pollution in the THz range. Fully bioderived THz shields could be a sustainable solution to transcend towards a biocarbon economy. Herein, we report an environmentally benign and facile approach to fabricating 3D porous ultra-light aerogels and flexible nanopapers from cellulose nanofibers and highly conductive biocarbon fully derived from biomass. These functional constructs showcased excellent broadband THz shielding performance in both sub THz (W band) and THz region (0.4–2.0 THz). The THz shielding effectiveness of a 600 µm thick nanopaper and 3.00 mm aerogel was found to be 46 dB and 70 dB, with superior THz absorption behaviour and minimal reflection of THz signals. The electronic structure and charge transfer properties were examined under an external electric field based on density-functional theory. The results show that the effect of the external electric field induces intramolecular charge transfer from the lower-graphitic sheet to the upper-graphitic sheet of the nanocomposite suitable for THz excitation. Moreover, these sustainable absorbers could deliver similar THz shielding performance compared to graphene foam (74 dB), exemplifying their humungous potential as advanced functional materials for futuristic THz devices.

Double broadband enhanced absorber based on graphene-coupled metal disk resonator structure

A double broadband terahertz absorber based on nonstructured graphene with a dielectric coupled gold disk structure was investigated in this paper. The results show that one absorption band can be switched from reflection state (“OFF”) to absorption state (“ON”), and the other absorption band can be switched from reflection state (“OFF”) to absorption state (“ON”), with bandwidths of over 90% absorption ranging from 0.46 to 1.4 THz and 2.38 to 3.35 THz, respectively. Furthermore, the double broadband terahertz absorber has polarization and background refractive index insensitivity. The Fabry Perot resonance between the graphene sheet and the bottom gold reflector is primarily responsible for the double broadband absorption in graphene, which can be enhanced by the addition of a gold disk resonator. Because of the aforementioned properties, the proposed absorber has potential applications in multiple optical switches, terahertz photoelectric detectors, modulators, and sensors.

Multimode tunable terahertz absorber based on a quarter graphene disk structure

In this research work, in order to solve the unadjustability of traditional noble metal absorbers to meet the complex application requirements in the actual electromagnetic environment, we designed a simple tunable absorber based on graphene with tunable Fermi level. The performance of the proposed absorber is theoretically simulated by the finite difference time domain (FDTD) method. The proposed absorber has two perfect absorption peaks with high efficiency of 99.51% and 99.548% in its working band (90–155 μm). We have performed an in-depth analysis of the causes of perfect absorption and focused on the tunability of the absorber. The absorption frequency can be adjusted by controlling the relaxation time and Fermi level of graphene, and the same purpose can be achieved by changing the refractive index (relative dielectric constant) of the medium. In addition, we also explored the influence of the change of the top structure parameters on the absorption performance. The proposed absorber has the ability to adapt to different electromagnetic environments. In general, it can be flexibly regulated in practical applications, which will provide new possibilities for the development of many fields such as detection and communication.

Review on Terahertz Metamaterial Absorbers

Abstract: Absorbers are devices that internally consume electromagnetic waves to partially or completely attenuate them. The basic idea is to absorb electromagnetic radiation by resonating the intended surface with the incident electromagnetic waves. This article focuses on the development of the absorber (from single-band to multi-band, narrow to broadband, non-tunable to tunable, and so on). The basic absorption principle of the current popular and excellent metamaterial graphene absorber is provided, as is the theoretical explanation of impedance matching and how to attain critical performance metrics like tunability, as well as prospects for terahertz (THz) absorber applications. Finally, numerous innovative absorbers are shown as examples, providing new ideas for future researchers.

Multilayer graphene-enabled structure based on Salisbury shielding effect for high-performance terahertz absorption.

Sandwich-type structure based on Salisbury screen effect is a simple and effective strategy to acquire high-performance terahertz (THz) absorption. The number of sandwich layer is the key factor that affects the absorption bandwidth and intensity of THz wave. Traditional metal/insulant/metal (M/I/M) absorber is difficult to construct multilayer structure because of low light transmittance of the surface metal film. Graphene exhibits huge advantages including broadband light absorption, low sheet resistance and high optical transparency, which are useful for high-quality THz absorber. In this work, we proposed a series of multilayer metal/PI/graphene (M/PI/G) absorber based on graphene Salisbury shielding. Numerical simulation and experimental demonstration were provided to explain the mechanism of graphene as resistive film for strong electric field. And it is important to improve the overall absorption performance of the absorber. In addition, the number of resonance peaks is found to increase by increasing the thickness of the dielectric layer in this experiment. The absorption broadband of our device is around 160%, greater than those previously reported THz absorber. Finally, this experiment successfully prepared the absorber on a polyethylene terephthalate (PET) substrate. The absorber has high practical feasibility and can be easily integrated with the semiconductor technology to make high efficient THz-oriented devices.

Broadband terahertz absorber based on the coupling between Au and graphene

A simply designed broadband meta-absorber (MA) that works in terahertz (THz) band is proposed and investigated. The reflector substrate of the MA is composed of nickel. The middle layer of this structure is made of dielectric Al2O3, which serves as a dielectric layer between the nickel and the metasurface layer. The metasurface layer comprises a graphene ring with a disk-like Au in the center. The wideband absorption mechanism benefits from the hybridized surface plasmonic modes caused by the coupling between the Au disk and the graphene ring. Besides, with the adhesion of the top Au metal disk, Fabry-Perot cavities formed by the top Au and the bottom metal produce the continuous cavity resonant modes also to enhance surface hybridization plasmons. Because the proposed broadband MA is symmetrical, it is insensitive to polarization and has a good bearing angle of 0 deg to 70 deg. The results of our study may inspire specific applications of wave modulation, including THz imaging, detecting, modulation, and sensing.

Tunable and switchable terahertz absorber based on photoconductive silicon and vanadium dioxide

In this paper, a tunable and switchable absorber based on photoconductive silicon (Si) and vanadium dioxide (VO2) is proposed. The designed absorber can achieve tunable bifunctional single-/dual-band absorption and switchable perfect absorption, by optically pumped silicon and temperature controlled VO2 individually or simultaneously. The absorption mechanism is explained by relative impedance theory. Moreover, a multiple interference model based on quasi-Fabry-Pérot cavity resonance is established to further reveal the principle of absorption, and the theoretical result is in good agreement with the numerical ones. Influence of structural parameters, polarization and angle of incident wave on absorption performances are systematically studied. The flexible tunable characteristics and polarization insensitivity of the designed absorber for multi-dimensional operation has potential applications in dynamic terahertz (THz) devices.

Band reduplication of perfect metamaterial terahertz absorber with an added layer: cross symmetry concept

Band reduplication of perfect metamaterial terahertz absorber with an added layer: cross symmetry concept