Traditional Absorber Research Articles

Dual-function terahertz metamaterial absorber based on microfluidic structures

In recent years, terahertz metamaterial sensors have shown great potential in label-free biosensing; yet, the detection of high-absorption liquid samples that are sensitive to terahertz waves remains a significant challenge. In this study, a dual-function absorber capable of dynamically switching between broadband absorption and high-sensitivity sensing is proposed based on the microfluidic technology and phase change characteristics of vanadium dioxide (VO2). Compared with traditional terahertz microfluidic sensors, this structure differs in that it incorporates a VO2 film as a separation layer in the sensor cover plate and a VO2 square resonator on top. This configuration not only exhibits high-sensitivity sensing but can also function as an absorber for broadband absorption. When VO2 is in the metallic state, the structure acts as a broadband absorber with an absorption rate exceeding 90% across the 1.09–3.02 THz range. When VO2 is in the insulating state, the structure functions as a microfluidic sensor, achieving an absorption rate above 99.9% at 1.438 and 2.068 THz, with nearly perfect absorption and refractive index sensitivities of 532 and 785 GHz/RIU, respectively; the quality factor is 17.6 and 23.5, respectively, indicating excellent sensing performance. Moreover, due to the symmetry of the metal micro-structured layer and the VO2 square resonator, the device exhibits polarization insensitivity and stability at large incident angles. In summary, this structure significantly broadens the applications of traditional absorbers and sensors and holds promise for future applications in electromagnetic cloaking, energy harvesting, and biomedical detection.

A Novel Full‐Band Microwave Absorber Based on Scattering Enhanced Prism‐Honeycomb Nested Structure

AbstractWith advancements in radar detection technology, electromagnetic stealth has garnered significant attention in military applications. Traditional electromagnetic absorbers typically focus on tuning electromagnetic parameters; however, they are often limited by material constraints, resulting in effective absorption only within narrow frequency bands. This work presents a novel prism‐honeycomb nested microwave absorbing structure, inspired by the scattering phenomenon of light waves in a prism, which utilizes an enhanced scattering effect. The varying impedances of electromagnetic waves (EMWs) in different media lead to transmission and reflection that adhere to Snell's law at the interfaces. To optimize the scattering effect, the inner prism is filled with a high transmittance material, while the outer honeycomb structure incorporates a material with high dielectric loss. Consequently, electromagnetic waves experience significant attenuation within the unit. Despite a thickness of only 7 mm, this structure achieves over 90% EMW absorption across a broad frequency range of 1–18 GHz. Additionally, the honeycomb structure exhibits excellent mechanical load‐bearing capacity. The nesting of the prism further enhances support points, resulting in a compressive strength of 16.4 MPa. This innovative design not only facilitates full‐band absorption but also provides high mechanical load‐bearing capabilities, offering valuable insights for applications in electromagnetic stealth and camouflage.

Preparation and electromagnetic waves absorption performance of novel peanut shell/CoFe2O4/(RGO)x/PVA nanocomposites

Novel functional materials possessing the capability to attenuate electromagnetic energy are being increasingly incorporated into home decor as concerns over excessive electromagnetic radiation pollution continue to grow. The properties of magnetism and dielectricity in the flexible peanut shell/CoFe2O4/reduced graphene oxide/polyvinyl alcohol (PS/CF/(RGO)x/PVA) nanocomposites can be finely tuned by adjusting the amount of RGO in the mixture. An examination of the composite’s absorption capabilities revealed a direct link between higher RGO content and enhanced absorption. Due to the presence of multiple pathways for electromagnetic wave transmission through the three-dimensional porous structure, as well as the synergistic effects of dielectric-magnetic properties and various defects in the carbon derived from peanut shells, the PS/CF/(RGO)x/PVA nanocomposites exhibit remarkable impedance matching and exceptional attenuation capabilities to -20.98404 dB for a thickness of 1 mm. Additionally, the PS/CF/(RGO)x/PVA nanocomposites have shown great promise in the production of flexible electronic devices like light-dependent resistors. Their lightweight and flexible nature play a crucial role in their success in this application. It is worth mentioning, however, that these nanocomposites bear a resemblance to traditional absorber equipment used in the industry.

Schottky Interface Engineering in Ti3C2Tx/ZnS Organic Hydrogels for High‐Performance Multifunctional Flexible Absorbers

AbstractWith the rapid advancement of wearable electronics, soft robotics, and camouflage technologies, there is an urgent demand for flexible, multifunctional electromagnetic wave absorbing materials. Traditional absorbers, including metal‐ and carbon‐based materials, often lack the flexibility required for such applications. In this work, a novel strategy is proposed for developing a flexible absorber by combining a conductive filler with a Schottky heterogeneous interface and a polymer network framework. Ti3C2Tx MXene is modified with ZnS via a low‐temperature hydrothermal method, forming a Ti3C2Tx/ZnS composite. This composite is subsequently embedded in a copolymer matrix of polyvinyl alcohol (PVA) and acrylamide (AAm), dispersed in a binary water‐glycerol solution. The Schottky interface between Ti3C2Tx and ZnS enhances electron transfer at the heterophase boundary, significantly improving interface polarisation. Simultaneously, interactions between water and glycerol restrict the rotation of polar molecules under external electromagnetic fields, optimising polarisation loss within the gel. Experimental results demonstrate that the Ti3C2Tx/ZnS gel achieves a minimum reflection loss (RLmin) of −43.76 dB at 8.79 GHz, with an effective absorption bandwidth (EAB) covering the entire X‐band. Additionally, the gel exhibit exceptional stretchability, frost resistance, shape adaptability, and photothermal conversion properties.

Development of a New Correlation Model for Heat Transfer in Solar Air Heater with Corrugated Absorber Plates Using Swarm Optimization

Solar air heaters play a crucial role in distributing heated air at low to medium temperatures. The heart of these systems lies in the absorber plate, which directly absorbs solar heat energy and then efficiently transfers it to the flowing air. However, the challenge lies in achieving optimal thermal efficiency by modifying the absorber plate roughness. Traditional smooth absorber plates have a limited contact area for heat transfer, leading to suboptimal performance. Using passive techniques, such as corrugation on the absorber plate, may increase thermal efficiency by creating turbulence in the laminar sublayer. In this study, corrugated solar air heaters are considered, with the absorber plates roughened into square, semicircular, and triangular ribs. The flow characteristics of heat due to the roughness of the absorber plate is simulated using the computational fluid dynamic (CFD) technique. The ANSYS Fluent 2019R3 is used to investigate the turbulent air flow in the absorber plate. The simulation analyses are performed over a Reynolds number range of 4000–18,000 using three different pitches. As the main contribution, two different model equations, namely M1 and M2, for the correlation model of the solar heat transfer were proposed to predict the Nusselt number, where M2 is an original model and M1 is newly established with the fine-tuned coefficients. Also, for the first time in the literature, the recent swarm optimization algorithm, namely Honey Formation Optimization with Single Component (HFO-1), is used to optimize the solar air heater and a comparison study with a popular non-swarm optimization, namely the Generalized Reduced Gradient (GRG) optimization, is provided. The Nusselt number was obtained using HFO-1 with a percentage error (MAPE) of 2.15% and 0.86% for the models M1 and M2, respectively. Moreover, the average achievement of HFO-1 on the proposed correlation models is 50% better than that of the GRG optimization, with respect to the RMSE.

Dynamic characteristics and transmission efficiency of energy-harvesting shock absorber with low speed and heavy duty capacity

Traditional hydraulic shock absorbers commonly encounter challenges such as cavitation, oil leakage, and the management of energy dissipation. The proposed regenerative shock absorber, which utilizes a ball screw mechanism, offers advantages such as high efficiency and heavy load capacity. This paper focuses on the design, modeling, and testing of a mechatronic shock absorber. Virtual prototype simulation techniques are employed to investigate the dynamic behaviors of the shock absorber. The paper presents a systematic efficiency model of a shock absorber, which is based on the ball screw and gearbox mechanisms. The study comprehensively analyzes the effects of rotation speed, axial load, and structure parameters on transmission efficiency. The results demonstrate that a peak power of 38 W can be achieved with a damping force of only 340 N, and the recovery efficiency can reach up to 28%. The experimental test results validate the effectiveness and reliability of the proposed dynamic and efficiency models. The originality of this study lies in the development of a novel energy-harvesting shock absorber with a ball screw mechanism in series with a gearbox, which shows excellent energy recovery potential and transmission efficiency under low speed and high duty conditions.

An adaptive assisted method based on MOPSO for THz MMA effective designing

Abstract To address the high time cost and low efficiency of traditional terahertz metamaterial absorber design, an adaptive method based on multi-objective particle swarm optimization was proposed. First, we presented a symmetric absorber of a four-split-ring resonator with a cross-shaped top layer. The structural parameters were optimized by the particle swarm optimization and multi-objective particle swarm optimization algorithms. The simulation results indicated that the multi-objective particle swarm optimization rapidly obtained geometric parameters that balance the high absorptivity and high quality factors. This method quickly identified a symmetric structure with absorptivity greater than 99% and quality factor of 377.45 at 1.584 THz. Additionally, the asymmetric structure achieved near-perfect absorption at 1.585 THz with a Q value of 281.32. By studying the electric field distribution and the surface current distribution, the physical mechanism of the absorber designed has been explained. This adaptive assisted method based on multi-objective particle swarm optimization can efficiently design metamaterial absorbers and offer an artificial intelligence strategy for terahertz functional device design.

Control Voltage Effect on Operational Characteristics of Vehicle Magnetorheological Damper

Considering the increasingly large-scale application of magnetic fluids in various industries, we can confidently state that in the near future magnetorheological dampers will be widely used in adaptive automotive suspensions due to their operational flexibility and simplicity of controlling damping forces by changing the magnetic fluid properties according to parameters of surrounding electromagnetic field. The antivibration efficiency during operation is achieved by regulating the hydraulic resistance of the “magnetic” shock absorber by applying voltage to the windings of its coil. In addition to the physical properties of the oil used in the “magnetic” shock absorber, the viscosity of the working magnetorheological fluid is greatly influenced by the shape of the control signal. The paper focuses on the theoretical aspects of constructing a mathematical model of ac magnetorheological damper and presents the results of a computer experiment to assess effectiveness of its use as part of the adaptive suspension a passenger vehicle. In this case, the actual parameters of the “magnetic” shock absorber, used in modeling the dynamic process, were determined experimentally on a test bench, and the adequacy of the developed mathematical model was confirmed by the results of a semi-natural experiment. Using a verified model, the magnetorheological damper characteristics were obtained and compared for various forms of control signal, including rectangular voltage pulses of various frequencies and duty cycles, sinusoidal pulses and constant voltage signals. The analysis of the antivibration efficiency was carried out on the basis of the developed “quarter” model of a semi-active car suspension with a verified submodel of a magnetorheological damper integrated into its structure. Moreover, the simulation scenarios were based on the selected strategy for controlling the voltage supplied to the windings of the “magnetic” shock absorber. As the results of theoretical and experimental studies have shown in terms of energy consumption, expansion of the working area of the damping characteristic and achieving smooth control of the damping force, the most effective is the use of a sinusoidal pulse voltage signal in the control circuit, which ensures a reduction in both the amplitude and damping time of oscillations. However, when de-signing and manufacturing a controller, creating a pulse modulator for generating sinusoidal pulses coinciding in phase and frequency with the vibrations of the car body is very difficult due to the random nature of external disturbances from the road surface. When a constant voltage is applied to the magnetorheological damper winding, the damping properties of the suspension are also improved compared to the basic design based on a traditional hydraulic shock absorber. Moreover, there is a proportional relationship between the voltage supplying the damper, the amplitude and damping time of the vibrations of the car body is observed. An increase in the control signal voltage from 1 to 2 V leads, in comparison with passive control of a magnetic shock absorber, to a decrease in the maximum amplitude of vibrations of the car body by 6.25 and 11.25 %, respectively, and a decrease in the vibration damping time by 0.72 and 1.41 s.

Tilted Wire Metamaterials Enabling Ultra-Broadband Absorption from Middle to Very Long Infrared Regimes

Infrared metamaterial absorbers underpin many entrenched scientific and technical applications, including radiative cooling, energy harvesting, infrared detectors, and microbolometers. However, achieving both perfect and ultra-broadband absorption remains an unmet scientific challenge because the traditional metamaterial absorber strategy suffers from complex multi-sized resonators and multiple meta-element patterns. We demonstrate a simple ultra-broadband infrared metamaterial absorber consisting of tilted graphite wires and an Al reflector. The proposed tilted wires-based metamaterial (TWM) absorber exhibits absorption of above 0.95 across the middle to very long-wavelength infrared spectrum (3–30 µm). By increasing the aspect ratio, the bandwidth can be expanded and achieve near-perfect absorption in the 3–50 μm spectral range. The excellent infrared absorptance performance primarily originates from the ohmic loss induced by the electromagnetic coupling between neighboring tilted wires. Furthermore, we propose a typical three-layer equivalent model featuring a resonator/insulator/reflector configuration that requires more than 84 resonant cavities to obtain comparable infrared absorptance. Our high-performance TWM absorber could accelerate the development of next-generation infrared thermal emitters and devices and other technologies that require infrared absorption.

Genetic-algorithm-assisted design of chiral honeycomb membrane acoustic metamaterials for broadband noise suppression

Low-frequency sound wave reduction is hardly feasible for traditional sound absorbers such as porous media. In contrast, locally resonant acoustic metamaterials act as spatial frequency filters, effectively reducing low-frequency noise. However, these materials can have narrow bandgaps, add extra mass to the main system, and function only within a specifically adjusted frequency range. Therefore, this paper proposes a methodology for designing three-dimensional (3D) chiral honeycomb membrane-type acoustic metamaterials (MAM) based on acoustic circular dichroism (ACD), negative effective mass, and local resonance mechanisms (LRM). The paper also uses the genetic algorithm (GA) to maximize sound transmission attenuation and widen bandgaps. The accuracy of the simulations is validated with available experimental data. The key idea of the present study is to automatically design a MAM structure using modern optimization tools. A developed GA aims to maximize the average sound transmission loss (STL) across the desired low-frequency range of 0–850 Hz by optimizing the value of structural parameters associated with the configurations of masses, including rotation and linear offset, as well as their geometrical dimensions, including length and width. COMSOL Livelink with MATLAB is employed as a practical co-simulation tool to find an optimum value for structural parameters. Results indicate a 35% improvement in average STL along with an ultra-wide bandgap with a 507% bandgap coverage factor (BGCF) in the frequency range of interest, verifying the reliability of the developed algorithm. In addition, sound mitigation incidence is justified by exploring the negative effective parameters of the unit cell and displacement vector fields. The proposed designs demonstrate superior performance as both initial and optimized models broke the mass law within the investigated frequency range. Finally, the effect of the selected geometrical parameters on the objective function is observed through sensitivity analysis. This study presents the practical use of optimization algorithms to develop MAMs.

Experimental analysis of solar desalination system performance with graphene and graphitic carbon nanopaint-coated solar absorbers

Improving the efficiency of basin-type solar stills is crucial for ensuring reliable access to clean water in areas facing water scarcity. One effective way to increase water yield production is by applying various coatings to the solar still's absorber plate. Using nanocoatings on solar absorber plates increases solar radiation absorptivity and minimizes reflectivity, which helps improve water production. In this proposed work, Graphene nanoplatelets (GNPs)-based nano paint, graphitic carbon nanoparticles (GCNPs)-dispersed black paint, and conventional black paint were applied to the solar still's absorber plate. According to the study, the GNPs' nano paint resulted in a cumulative solar still productivity that was 48.23 % higher than the GCNPs-dispersed black paint and 10.28 % higher than the conventional black paint. It also revealed that the energy efficiency of solar stills with GCNPs and GNPs nano paint-coated absorbers was 56.96 % and 69.77 %, respectively, while the traditional black paint-coated absorber managed only 39.42 %. The calculated exergy efficiency of these three solar stills was 8.55 % for the conventional black paint, 13.93 % for the GCNPs, and 22.93 % for the GNPs nano paint-coated absorber. This proposed system also has an energy payback period of 1.79 years and contributes to achieving a carbon credit of $994.90 through the market. The cost of distilled water in this system is also 0.016$/L.

High-entropy TiVNbMoC3Tx MXene hybrid with balanced dielectric-magnetic loss for high-efficient electromagnetic wave absorption with environmental stability

With the advent of the 5G era, there is a growing demand for electromagnetic wave (EMW) absorbers that offer both efficient absorption and improved environmental stability. Transition metal carbides/carbonitrides (MXene), with their atomic-layered structures and high electrical conductivity, offer substantial potential for crafting efficient electromagnetic functional materials. Yet, enhancing the antioxidant capabilities and addressing the poor loss mechanisms of traditional MXene absorbers remain challenging tasks. In this context, a TiVNbMoC3Tx high-entropy MXene (HE-MXene) and its magnetic hybrids were synthesized for the first time. The unique multicomponent structure of high-entropy MXene reduces grain boundary formation, thereby slowing the progression of oxidation reactions. The incorporation of magnetic nanoparticles induces interface polarization loss or strong magnetic coupling, thereby enhancing EMW attenuation. These magnetic HE-MXene hybrids demonstrated a minimum reflection loss of −57.59 dB at a matching thickness of 1.46 mm and an effective absorption bandwidth (EAB) of 4.72 GHz at a thickness of 1.53 mm. Furthermore, the magnetic hybrids also exhibited outstanding oxidation and electrochemical corrosion resistance. This research provides valuable theoretical insights for the development of electromagnetic composites within high entropy (HE) systems, showcasing significant potential for long-term applications.

Shifting d‐band Center: An Overlooked Factor in Broadening Electromagnetic Wave Absorption Bandwidth

AbstractAbsorption bandwidth is one of the key performance metrics for electromagnetic wave (EMW) absorbers. Traditional oxide absorbers, despite their merits such as abundance, long‐term stability, and low cost, have long been plagued by their inferior absorption bandwidth (typically less than 4 GHz). Herein, a novel concept is proposed: the introduction of cation vacancies and heterostructures into oxides can remarkably broaden their absorption bandwidth. A broadening value of 7.75 GHz is observed through this route, surpassing the broadening achieved by other existing engineering methods, by ≈100%. Crucially, this study discovers that a negative shift in the d‐band center, a previously overlooked factor, is responsible for this broadening phenomenon. By inducing cation vacancies and heterostructures, a negative shift in the d‐band center gives rise to an increase in carrier concentration and promotion of charge separation, resulting in higher conductive and polarization losses, ultimately leading to a broader absorption bandwidth. The applicability of this concept is validated in another distinctly different system, where the absorption bandwidth also experiences a remarkable increase (from 0 to 6.86 GHz). This study offers significant implications for designing wide bandwidth EMW absorbers and expands their applications in various scenarios such as wearable electronics and artificial intelligent devices.

Constructing multi-polarization in metal–organic framework gels for electromagnetic wave absorption via ethanolamine hetero-coordination

Metal–organic framework (MOF) gels offer the potential for tunable electromagnetic wave (EMW) absorption owing to their customizable MOF cross-linked networks and strongly polar liquids. This overcomes the drawbacks of traditional MOF-derived absorbers; however, the corresponding EMW loss mechanism is absent. Here, a zeolite imidazole framework (ZIF) was used as a functional unit in conjunction with ethanolamine (EtA) hetero-coordination and methanol to fabricate ZIF organogels with the desired EMW absorption. The pore size of ZIF maintains the permeability for EtA and the methanol-barrier properties, which results in the formation of free –NH2 and associated –NH2 for EtA. The two corresponding species of dipole polarization losses provide additional EMW attenuation. Furthermore, the intensity inversion of the dual relaxation modes caused by the change in the size of the ZIF colloidal particles was used to improve the EMW absorption for the first time. ZIF organogels exhibited a strong correlation between dielectric properties and metal node species/EtA coordination density/hydrogen bonds, indicating that the absorption properties can be accurately regulated. Me-ZnCo-1 sample demonstrates the optimal effective absorption bandwidth of 6.59 GHz at 2.19 mm. This study not only elucidates the EMW loss mechanism of ZIF organogel networks but also proposes a creative design strategy for EMW-absorbing MOF gels.

Quenching Vibration on a Symmetric Laminated Composite Plate Excited by Multiple Harmonics Using Inerter-based Dynamic Vibration Absorbers

Abstract In this paper a simple and efficient method is developed to quench the steady state vibration of a symmetric laminated composite rectangular plate subjected to multiple harmonics with distinct excitation frequencies. The introduction of the inerter into the traditional dynamic vibration absorber enlarges the solution space for both the feasible attachment locations and the absorber parameters. For a given set of attachment locations, when the traditional vibration absorbers yield physically unrealizable absorber parameters, i.e., negative absorber parameters, an inerter-based vibration absorber can be used such that the absorber parameters become strictly positive. Using the assumed modes method, the governing equations of the laminated composite plate carrying the inerter-based dynamic vibration absorbers are first formulated. A set of constraint equations is established by enforcing nodes at user-specified locations on the plate. Harmonic excitations consisting of a single or multiple distinct excitations are considered. In addition, two attachment scenarios are analyzed: when the attachment and node locations coincide, and when they are distinct. Numerical experiments show that the absorbers parameters can be readily determined for both cases, and validate the proposed method of enforcing the desired node locations when the plate is subjected to either a single or multiple harmonic excitations.

Impact of CuO nanoparticles on the viscosity and vibration damping characteristics of shock absorber oil

This study investigates the potential of copper oxide (CuO) nanoparticles as additives to enhance the viscosity and vibration-damping characteristics of shock absorber oil. Shock absorbers play a critical role in vehicle safety and handling by mitigating vibrations from road irregularities. However, their effectiveness deteriorates over time. To address this, CuO nanoparticles were explored for their ability to improve lubricant performance. Nano-lubricants were prepared by dispersing CuO nanoparticles at varying concentrations of 0.25 wt%, 0.5 wt%, 1 wt%, and 1.5 wt% in a base oil using ultrasonication. The novelty of this research lies in the innovative use of CuO nanoparticles to significantly enhance the viscosity and vibration-damping properties of shock absorber oil. The viscosity of these nano-lubricants increased significantly, with the 1 wt% CuO nano-lubricant achieving a 20% increase at 25 °C compared to the base oil, indicating improved load-carrying capacity and potential friction reduction. Vibration damping performance was evaluated using a dedicated shock absorber test rig. The nano-lubricants exhibited reduced overall vibration acceleration compared to plain oil, with a 15% improvement in damping effectiveness at the optimal CuO concentration. However, the transmissibility ratio, a key damping metric, did not show significant variation, suggesting that traditional shock absorber designs might require modifications to fully leverage the benefits of CuO nanoparticles. These findings demonstrate the potential of CuO nanoparticles to enhance the viscosity and damping characteristics of shock absorber oil, leading to improved performance at lower temperatures.

Wideband optically transparent absorber based on multilayer ITO films with high absorption rate.

In this paper, a wideband optically transparent absorber based on multilayer indium tin oxide (ITO) films is designed, fabricated, and measured. The structure uses polyethylene terephthalate (PET) and ITO films to replace the dielectric substrate and metal pattern of the traditional absorber to achieve optical transparency characteristics. The absorption of the proposed absorber is above 90% from 4.92 to 24.55 GHz and exceeding 95% in the range of 5.74 ∼ 21.85 GHz, respectively, under normal transverse electric (TE) and transverse magnetic (TM) polarized incidences. Moreover, it shows outstanding stability with various incident angles over a wide range. A prototype of the proposed absorber is fabricated and experimentally verified, with good measurement results. The optical transparency and great absorption performance make the absorber a promising candidate for transparent electromagnetic compatibility.

The Stiffness and Damping Characteristics of a Rubber-Based SMA Composite Shock Absorber with a Hyper-Elastic SMA-Constitutive Model Considering the Loading Rate.

Shock absorbers are essential in enhancing vehicle ride comfort by mitigating vibrations. However, traditional rubber shock absorbers are constrained by their fixed stiffness and damping properties, limiting their adaptability to varying loads and thus affecting the ride comfort, especially under extreme road conditions. Shape Memory Alloys (SMAs), known for their intelligent material properties, offer a unique solution by adjusting stiffness and damping in response to temperature changes or strain rates, making them ideal for advanced vibration control applications. This study builds upon the Auricchio constitutive model to propose an enhanced SMA hyper-elastic constitutive model that accounts for different loading rates. This new model elucidates the impact of loading rates on the stiffness and damping characteristics of SMAs. Additionally, we introduce an innovative circular rubber-based SMA composite vibration reduction structure. Through a parameterized model and finite element simulation, we comprehensively analyze the stiffness and damping properties of the composite damper under various loading rates and harmonic excitations. Our findings suggest a novel approach to improving the vehicle ride comfort, offering significant potential for engineering applications and practical value.

Polarization-insensitive terahertz ultra-wideband absorber with an actively tunable bandwidth

This study presents a novel, to our knowledge, polarization-insensitive terahertz absorber with an actively adjustable bandwidth. The absorber consists of a vertically stacked three-layer structure with target-shaped resonant layers. Its absorption bandwidth is dynamically controlled, exhibiting ultra-broadband characteristics in the metallic phase. The absorber achieves over 90% absorption from 1.8 to 31.7 THz, with a relative bandwidth of 178%. In the insulating phase, the device transforms into a narrowband absorber, showing a precise absorption peak within the 0 to 20 THz frequency range. Notably, this absorber demonstrates polarization-insensitive and wide-angle absorption properties, making it suitable for different application scenarios. Compared to traditional broadband absorbers, the absorber proposed in this study features an ultra-wide absorption bandwidth and switchable operating modes, enhancing its flexibility and adaptability. The excellent performance of the absorber indicates its suitability for various applications, such as sixth-generation (6G) wireless communication, security detection, imaging, military stealth technology, and energy harvesting.

Graphene-based tunable broadband metamaterial absorber for terahertz waves

In order to overcome the limitations exhibited by traditional absorbers in electromagnetic wave absorption, such as the extremely narrow absorption bandwidth and uncontrollable absorption results, this paper proposes a novel tunable broadband metamaterial absorber based on graphene. Compared to other terahertz absorbers, the absorber designed in this study exhibits simpler structural design, compact form, thin thickness, efficient absorption performance, and a broader bandwidth. This absorber adopts a three-layer structure, including a patterned monolayer graphene metasurface, a dielectric layer, and a metal substrate. The structure of this patterned graphene consists of four triangular graphene resonators, achieving both high absorption efficiency and maintaining an exceptionally wide absorption bandwidth. The simulation results indicate that at a Fermi energy level Ef of 0.45 eV, the absorber achieves a broadband absorption rate of over 90 % in the 3.287 THz to 5.247 THz frequency range under normal terahertz wave incidence conditions. By analyzing different quantities of the triangular graphene structure on the top of the absorber, we found that the wide absorption bandwidth of the absorber is mainly attributed to the structural coupling of the top-layer graphene in the absorber. Furthermore, through the study of electric field amplitude and current distribution, we stumbled upon that when terahertz waves are incident on the absorber, due to the structural coupling between the graphene layers, electric resonance and magnetic resonance occur within the absorber, resulting in the absorption effect. Finally, through the study of geometric parameters, different polarization angles and oblique incidence angles of the incident waves, as well as different Fermi energy levels of graphene, we discovered that by adjusting the Fermi energy level of graphene, the bandwidth and absorption performance of the absorber can be flexibly tuned. In addition, this absorber exhibits wide-angle absorption characteristics and polarization-insensitive properties, providing potential application prospects in fields such as terahertz thermal imaging and stealth technology.