Design Of Absorber Research Articles

Graphene-based polarization insensitive structure of ultra-wideband terahertz wave absorber

Graphene, a new smart material, has gained a lot of attention recently because of its tunable band structure and strong light-matter interaction. In comparison with typical absorbers, graphene absorbers have emerged as a highly attractive substitute for various types of applications. To broaden the absorption bandwidth, a two-dimensional graphene-based ultra-wideband and polarization-insensitive novel terahertz (THz) absorber with absorption over 95 % from 3.0 THz to 8.5 THz is proposed, with peak absorption of 99.9 % at 6.6 THz and average absorption of 98.4 % for the 5.5 THz bandwidth. The surface plasmon increased by the gold-graphene structure, the Mei resonance, and the interference cancellation between metasurfaces collectively contribute to the ultra-wideband absorption. To obtain nearly perfect broadband terahertz absorption, a single layer of graphene is used. The finite difference time domain (FDTD) approach is used for absorber analysis. In addition, the absorber is insensitive to the polarization angles and incidence angles of incident electromagnetic waves. The proposed graphene-based absorber dominates previously reported wideband THz absorbers in terms of over 95 % bandwidth, absorption peak value, and overall volume. This research will present a novel idea for the design of an ultra-wideband absorber, which can be considered a suitable candidate for different potential applications in terahertz imaging, sensors, photodetectors, and modulators.

Absorption-diffusion integrated stacked metamaterials by multi-compound strategy for broadband electromagnetic attenuation

The meta-structural design of flat absorbers demonstrates significant potential for improving microwave attenuation performance. However, the single mechanism of amplitude attenuation through resonance-enhanced effect necessitates considerable material thickness, restricting its application in electromagnetic (EM) defense. Utilizing the synergistic effect of multiple mechanisms is expected to break through the performance limits of microwave stealth metamaterials at the sub-wavelength scale. Herein, absorption-diffusion integration stacked metamaterials (ADISM) were designed using a multi-compound strategy, which comprises bionic porous spherical carbonyl iron powder (SCIP) coatings and stacked vortex metasurfaces (VMs). Such a metamaterial integrates EM scattering modulation with microwave absorption, enabling the creation of a broadband, high-efficiency, low-reflection design, providing an effective absorption bandwidth (EAB) reaching 10.42 GHz (7.58–18 GHz) at a thickness of 2.48 mm. Manipulating the orbital angular momentum (OAM) to effect wavefront transformation, the dissipation of EM wave energy is achieved. The absorption peak frequency modulation and absorption bandwidth broadening are achieved by the intrinsic loss capability of the porous coating, and corresponding mechanisms are demonstrated by simulation models. In short, the synergistic effects of microwave absorption and scattering modulation significantly enhance the return loss capability and facilitate broadband microwave attenuation. This research offers new insights into the multifunctional integration of EM stealth metamaterials.

Hollow engineering of Co/N-doped C@carbon aerogel with hierarchical structure boosting interfacial polarization for ultra-thin microwave absorption and thermal insulation

Rational manipulation of the composition and microstructure design of aerogel materials is considered to be an effective method for achieving the dual functions of microwave absorption and thermal insulation. Herein, hollow Co/N-doped C@carbon aerogel with hierarchical structures was designed and constructed via a synergistic strategy including directed freeze-drying, ZIF-67 in situ growth, chemical etching and calcination treatment. Co/N-doped hollow carbon nanocages derived from ZIF-67 with uniform heterojunctions and layered micro-mesopores were constructed using tannic acid and heat treatment process. After that, abundant macroporous structure from the carbon aerogel itself was further introduced to upgrade the impedance matching property, light weight and interfacial polarization loss capability. Remarkably, as-fabricated Co/N-doped C@carbon aerogel (ZTA@A-900) displays optimal MA performance with a minimum reflection loss (RLmin) value of −54.0 dB at 15.32 GHz and a broad effective absorption bandwidth (EAB) of 4.04 GHz (13.44–17.48 GHz) at a thickness of only 1.4 mm. Furthermore, the ideal CST simulation results and excellent thermal insulation property of ZTA@A-900 make it an outstanding candidate for microwave absorbers under extreme conditions. Thus, our work opens up a new avenue for the design and fabrication of multifunctional lightweight microwave absorbers.

Design of a Far-Infrared Broadband Metamaterial Absorber with High Absorption and Ultra-Broadband

We designed a metamaterial far-infrared absorber based on an MDM (metal–dielectric–metal) structure. We made a hollow crossed Ti microstructure at the top of the absorber. It is known that the coupling effect of equipartitional exciton resonance and intrinsic absorption at the surface of the depleting material has a strong influence on the absorber. Based on this, we investigated the absorption characteristics of the absorber using the Finite Difference in Time Domain (FDTD) theory. The results show that the absorber absorbed more than 90% of the light within a bandwidth of 12.01 μm. The absorber has an average absorption of 94.08% in the longwave infrared (LWIR) to ultra-longwave infrared (UWIR) bands (10.90–22.91 μm). The polarization insensitivity of the designed absorber is demonstrated by analyzing the absorption spectra of the absorber at different polarization angles. By adjusting the relevant geometric parameters, the absorption spectrum can be independently adjusted. Furthermore, the absorber exhibits good incidence angle insensitivity in both transverse electric (TE) and transverse magnetic (TM) modes. The absorbers are simple and easy to configure for applications such as optical cloaking, infrared heat emitters, and photodetectors. These advantages will greatly benefit the application of absorbers in practice.

Исследование адсорбционного разделения газовых смесей в условиях нестационарности

The influence of the initial concentration, rate and temperature of adsorption on the adsorption separation of gas mixtures (CO2, CH4, N2, H2S) is investigated. Components: N2 – 5%, H2S – 5%, CO2 – 5% and CH4 – 85%. And as an adsorbent granule of clinoptilolite of irregular shape were used. Isothermal adsorption of CO2 was obtained at different temperatures (293, 313, and 323 K). The obtained isotherms of CO2 adsorption showed that with an increase in temperature, the adsorption of CO2 decreased. The type of isotherms corresponds to Langmuir. The output curves of gas mixture adsorption depending on the gas flow rate and various main components of CO2 were also experimentally studied. The output curves of the adsorption of the CO2 component were studied at various gas flow rates of 20, 50, and 80 mL/min. Equilibrium time increases with a decrease in the gas flow rate. Output curves were also obtained depending on the initial CO2 concentrations of 5%, 10% and 20%. It was determined that with a decrease in the initial concentration of CO2, the equilibrium time also increases. Gas mixture components sorbed downwards: H2S→CO2→CH4→N2. The resulting system of model equations describing the adsorption separation of gas mixtures in a fixed adsorbent layer represents a complete mathematical model of the process under unsteady conditions. The obtained regularities of the process of adsorption of gas mixtures testify to the fact that the process takes place under non-stationary conditions. The proposed models for the optimal design of industrial absorbers can be used for adsorption separation of gas mixtures in the conditions of their unsteady flow.

Dielectric resonance of composites containing randomly distributed ZrB2 particles with continuous dual-peak microwave absorption

Substantial efforts have been devoted to the elaborate component and microstructure design of absorbents (inclusions) in microwave absorbing (MA) composite materials. However, the mesoscopic architecture of composites also plays a significant role in prescribing their electromagnetic properties, which is rarely explored in studies of MA materials. Herein, a composite containing randomly distributed ZrB2 particles is fabricated to offer a mesoscopic cluster configuration, which produces dielectric resonance. The resonance disappears and reoccurs when ZrB2 is coated with insulating and semiconductive ZrO2 layers, respectively, suggesting that it is a plasmon resonance excited by electron transport between ZrB2 particles in clusters rather than any intrinsic resonance of the materials constituting the composite. The resonance strength can be regulated by controlling the quantity of electron transport between particles, which is accomplished by gradually increasing the insulating ZrO2-coated ZrB2 ratio, x, to disturb the electron transport in ternary disordered composites containing ZrB2 and insulating ZrO2-coated ZrB2. When x exceeds 0.7, the electron transport is cut off completely and the resonance thus disappears. The resonance induces double quarter-wavelength (1/4λ) interference cancellations or resonance absorption coupled with 1/4λ interference cancellation, giving rise to continuous dual-peak absorption. This work highlights the significance of mesoscopic architectures of composites in MA material design, which can be exploited to prescribe electromagnetic properties.

Miura-ori based reconfigurable multilayer absorber for high-efficiency wide-angle absorption

Radar stealth structures that can achieve high-efficiency wide-angle absorption are key components of future military equipment. However, it is difficult for both planar and three-dimensional (3D) absorbers to achieve efficient absorption in a large incidence angle range. The multilayer reconfigurable absorber component based on Miura origami provides a unique solution. First, the multilayer origami absorber is parameterized in the simulation software. Each origami structure is covered with resistive films that fit the panels. Geometric constraints are satisfied among the multilayer structures. They support reconfigurability in the range of continuous states (as opposed to discrete states), which is conducive to finding the folded state with a more efficient absorption rate within the frequency band. Secondly, the designed structure does not require a specialized mechanically supported multilayer origami absorber. In addition, the equivalent analogue circuit method is used to analyze the efficient absorption of multilayer origami under oblique incidence. Finally, our proposed absorber satisfies the requirements of multiple absorption metrics: broadband, high efficiency, wide incidence angle, and polarization insensitivity. As the validation, we simulated and fabricated a double-layer origami absorber. Our proposed origami absorber can maintain an absorption rate of more than 90% for both transverse electric (TE) and transverse magnetic (TM) polarizations in the operating frequency band (5-20 GHz) over a wide range of incidence angles (0°-70°). When the incidence angle qinc = 40°, the double-layer origami absorber (q1 = 90°, α1 = 60°, and a2 = 75°) can achieve at least 10 dB reflection reduction of -18 dB and -20 dB in TE and TM modes, respectively. The proposed origami absorber provides a reference for the design of other absorbers.

Seismic performance enhancement of small modular reactors using optimal design of inerter-based vibration absorbers

Nuclear power plant (NPP) structures face significant challenges in ensuring structural resilience subjected to earthquake motions. The inerter-based vibration absorbers (IVAs) have been proven to control structural vibration, but they have not been applied in small modular reactor (SMR) structures. In this study, the optimal IVA parameters are investigated for SMR structures, which focus on reducing the seismic response of the first floor and fifth floor. By using a genetic algorithm (GA), the IVAs parameters are optimized to minimize the storey displacement variance and storey acceleration variance. Besides, the robustness analysis is performed to ensure the optimized parameters are practical. The various ground motions are selected for time history analysis (THA) to illustrate the seismic response of SMR equipped with the optimal IVAs. The results of THA demonstrate that the optimal IVAs enhance the seismic performance of the SMR compared with traditional SMR structures. By positioning optimal IVAs, significant mitigation of both storey displacement and storey acceleration are achieved. This study explores to a deeper understanding of IVAs' efficacy in SMR structures, which is beneficial to the practical use of IVAs in SMR structures.

Extremely asymmetric absorption and reflection near the exceptional point for three-dimensional metamaterial

In recent years, particular physical phenomena enabled by non-Hermitian metamaterial systems have attracted significant research interests. In this paper, a non-Hermitian three-dimensional metamaterial near the exceptional point (EP) is proposed to demonstrate extremely asymmetric absorption and reflection. Unlike its conventional counterparts, this proposed metamaterial is constructed with a loss-assisted design. Localized losses are introduced into the structure by combining our technique of graphene-based resistive inks with conventional printed circuit board process. Extremely asymmetric absorption and reflection near the EP are experimentally observed by tuning the loss between split ring resonators in the meta-atoms. Simultaneously, by linking the equivalent circuit model (ECM) with the quantum model, an equivalent non-Hermitian transmission matrix is constructed. We show that tuning the structure parameters of the ECM produces a metamaterial system with EP response. Our system can be used in the design of unidirectional metamaterial absorbers. Our work contributes to future works on the manipulation of EP to develop precision sensing and other applications in the 3D metamaterial platform.

On demand design of multi-freedom metamaterial absorbers based on recurrent prediction networks

Metamaterial absorbers (MMAs) have received a lot of attention due to their wide range of promising applications. In general, metamaterials involve a large number of geometric parameters, so the traditional simulation requires researchers to have rich experience and sufficient computational resources. In this paper, we demonstrate the forward and on demand design of multi-freedom MMAs based on the recurrent prediction network (RPN). We used the variable contribution analysis (VCA) algorithm to eliminate 55 absorption points whose contribution score was less than 1.0, the maximum fitting coefficient (R2) was increased by 7.0%, and the average calculation time was reduced by 20.326s. multi-freedom design is achieved by quantifying the design material into binary features as geometric parameter inputs into the RPN model. We solve the prediction peak error problem by many-to-one RPN, compared with the many-to-many prediction of classical deep neural network (DNN) model, the RPN error range is 0-0.12 compared to the 0-0.25 error range of the DNN. The ultra-wideband MMA design with the absorption of 0.2-4.2µm broadband is more than 90%, and the highest absorption rate is 99.2%. This method can be used in zoom imaging, metamaterials filters and other fields.

Comparative analysis of machine learning techniques for metamaterial absorber performance in terahertz applications

Metamaterial absorbers (MMAs) have tremendous potential for controlling and modulating Terahertz electromagnetic (EM) waves. It is challenging to design MMAs for optimal performance using conventional methods due to their time-consuming and computationally demanding nature. Machine learning (ML) regressor approaches have emerged as potential tools for optimizing the predictive modeling of MMAs in recent years. This article examined different regression techniques, such as Decision Tree, k-Nearest Neighbors, Random Forest, Extra Trees (ET), Extreme Gradient Boosting, Bagging, and Categorical Boosting. The primary goal is to assess the effectiveness of each regressor technique in forecasting the performance of MMAs using various performance metrics. The study focuses on a representative spectrum of MMAs, chosen for its key features that are common across a wide range of MMAs. The extra tree Regressor outperforms other models in the comparative analysis due to its capacity to integrate multiple decision trees and include randomness into the feature selection process, resulting in improved predictive skills. The ET regressor forecasts MMA performance remarkably well for a 70 % test size, with a Root Mean Squared Error of 0.0251, a Mean Absolute Error of 0.0074, a Mean Squared Error of 0.006, and an Adjusted R-squared of 0.9873. These findings can assist researchers in optimizing metamaterial absorber designs for Terahertz applications using ML regressor techniques and provide insights into how these methods can be generalized to other spectra with similar characteristics.

Design of an ultra-wideband and switchable VO2-based microwave absorber

We propose a design of an ultra-wideband microwave metamaterial absorber using Vanadium dioxide (VO2) based on a dual-layer structure. The ultra-wideband absorption performance of the proposed structure can switch by using the phase transition of VO2. When the VO2 is in the insulator state, the proposed absorber achieves an ultra-wideband absorption response in the range of 3.7–22.5 GHz with an absorptivity higher than 0.9 and a relative bandwidth of 143.5% at normal incidence, which covers the entire bands from the C to Ku. The designed absorber is polarization insensitive and wide incident angle stable for both transverse electric (TE) and transverse magnetic (TM) modes. Owing to the outstanding merits of absorption performance and frequency-tunable capability, our design structure can be suitable for many promising applications in the microwave range, such as smart radar, camouflage and stealth radome technology.

Accelerating multilayer frequency selective surface absorber design by combining equivalent circuit models with machine learning

Designing high-performance electromagnetic functional materials and artificial structures is of great significance for electromagnetic wave modulation applications. Optimizing performance in the high-dimensional parameter space of electromagnetic functional materials has posed a challenging problem. This paper proposes the use of reinforcement and transfer learning methods to facilitate the quick and accurate design of wideband circuit analog absorbers (CAA). A trained reinforcement learning network is utilized to comprehend the relationship between reflectivity performance and changes in impedance parameter. Furthermore, the transfer learning method is applied to accelerate the training process, leading in a 20-fold reduction in the number of simulations. To validate the effectiveness of this approach, a double-layer absorber aiming for reflectivity less than −20 dB at 3–10 GHz is designed, requiring only 50 simulations. This demonstrates that the proposed method provides a flexible strategy for the interactive design of equivalent circuit and electromagnetic structural parameters. Moreover, it presents a novel and efficient solution for microwave absorber design, with potential applications across various microwave design fields.

Regulating microstructure and composition by carbonizing in-situ grown metal-organic frameworks on cotton fabrics for boosting electromagnetic wave absorption

High-temperature carbonized metal-organic frameworks (MOFs) derivatives have demonstrated their superiority for promising electromagnetic wave (EMW) absorbers, but they still suffer from limited EMW absorption capacity and narrow bandwidth. Considering the advantage of microstructure and chemical composition regulation for the design of EMW absorber, hierarchical heterostructured MoS2/CoS2-Co3O4@cabonized cotton fabric (CF) (MCC@CCF) is prepared by growing ZIF-67 MOFs onto CF surface, chemical etching, and carbonization. Aside from the dual loss mechanism of magnetic-dielectric multicomponent carbonized MOFs, chemical etching and carbonization process can effectively introduce abundant micro-gap structure that can result in better impedance matching and stronger absorption capacity via internal reflection, doped heteroatoms (Mo, N, S) to supply additional dipolar polarization loss, and numerous heterointerfaces among MoS2, CoS2, Co3O4, and CCF that produce promoted conduction loss and interfacial polarization loss. Thus, a minimal reflection loss of −52.87 dB and a broadest effective absorption bandwidth of 6.88 GHz were achieved via tunning the sample thickness and filler loading, showing excellent EMW absorption performances. This research is of great value for guiding the research on MOFs derivatives based EMW absorbing materials.

Performance Evaluation and Cost Analysis of Photovoltaic Thermal (PVT) System Using the Triangular Shape of Absorber with Different Water-based Nanofluids as Coolants

The worldwide energy demand is continuously increasing, prompting experts to recommend using alternative energy sources to conserve natural gas, fossil fuels, and electricity. Photovoltaic thermal (PVT) systems emerge as a viable solution, generating electrical and heat energy simultaneously while freeing carbon dioxide (CO2) emissions. These systems offer sustainable green technology for supplying renewable electricity and heat to commercial and domestic applications. This study delves into the performance of a photovoltaic thermal (PVT) system featuring an isosceles triangular-shaped absorber design. It considers size variations of 0.02 and 0.03 m while maintaining a constant aspect ratio. Water-based nanofluids such as CuO/w, MgO/w, and ZnO/w, with a nanoparticle volume portion of 4%, alongside pure water as a coolant, are utilized with a variation of mass flow rate ranges from 0.028 kg/s to 0.11 kg/s, allowing for an exploration of its impact on performance parameters. A numerical model is established to comprehensively analyze the system's performance, applying an energy balance equation to its components. An economic analysis is also conducted to assess the system's cost-effectiveness and determine the energy payback time. Results indicate that the highest overall daily performance is achieved with ZnO/w nanofluid at a mass flow rate of 0.112 kg/s and a fluid flow channel size of 0.02 m. Comparatively, compared to other nanofluids and pure water, the average electrical, thermal, and overall performances achieved are 14.57%, 22.36%, and 36.40%, respectively. The energy payback periods are 5.5, 5.2, 5.4, and 4.8 years for CuO/w, MgO/w, ZnO/w, and Pure water, respectively. Furthermore, it is observed that a higher mass flow rate correlates with higher system performance parameters.

Collocated and non-collocated active spatial absorbers for spatial flexible structures

This article deals with the analysis and design of an active spatial mechanical vibration absorber and verification of its performance in collocated and non-collocated vibration absorption of a spatial flexible primary structure. The considered active absorber with six degrees of freedom has six identical natural frequencies. It is a so-called unifrequency absorber. The unifrequency property is achieved by delayed feedback, according to the concept of a delayed resonator. A proper tuning of the delayed feedback compensates the damping and variations in stiffness of mechanical parts, resulting in the behavior of an ideal absorber. The absorber was attached to a three-dimensional flexible frame with many degrees of freedom transformed to a reduced order model in modal coordinates. The use of a unifrequency absorber for two types of tasks is shown in this article. In the collocated case, the absorber is placed at the location where we want to suppress vibration. Such a placement is often not possible for various reasons. Therefore, the non-collocated absorber is also investigated which is remote from the point of desired vibration suppression. The absorber has considerable potential for use in improving the dynamic behavior of robots, complex rotor systems, and other mechanical systems suffering from unwanted fully spatial vibrations.

Design of ultra-thin multi-band sub-terahertz metamaterial absorber using three concentric ring resonators with same opening direction

In this paper, an ultra-thin sub-terahertz multi-band terahertz metamaterial absorber is proposed, its cell consists of three concentric ring resonators with the same opening direction, which can realize three discrete absorption peaks in the sub-terahertz frequency domain. The absorption peaks are mainly formed when the three open circular resonators interact with each other, and the superposition of the three discrete peaks creates a three-band absorption. The physical mechanisms of three-band absorption are illustrated by the electric fields and surface current distributions of three absorption peaks. Adjustment of the absorption effect could be obtained by altering the dimensions of the cleft circular resonator. By fixing the dimensions and changing the opening direction, these resonators will couple to each other and play an important role in regulating the frequency, intensity, and number of absorption peaks. Moreover, the multi-band metamaterial structure could be combined with vanadium dioxide, a phase change material, to actively modulate the absorption. In addition, the three-band metamaterial absorber has the characteristics of polarization-sensitive and wide-angle, which has extensive applications in the domains of security detection, biomedicine and communication.

Designing hybrid aerogel-3D printed absorbers for simultaneous low frequency and broadband noise control

Recent studies have demonstrated that granular aerogels with sub-50 μm particles surpass conventional acoustic materials like glass fibers and polyurethane foams in low-frequency sound absorption. However, incorporating such granular materials within practical structural solutions remains a challenge. In this study, we use additive manufacturing to overcome this challenge by designing a modular geometry that allows us to encapsulate such granular materials within a 3D printed scaffold. Using the 3D printed porous scaffold provides the added benefits of tunability and durability. Further, we introduce a design methodology and software tool to facilitate the efficient design of such hybrid sound absorbers. The proposed method uses the Johnson-Champoux-Allard model, Biot theory, and the transfer matrix method to model the acoustical behavior of hybrid absorber designs that use layered granular aerogels and 3D printed bulk absorbers. The tool can also be used to inversely characterize the acoustic bulk properties of such materials. We validate the design concept and tool by comparing the model predictions with experimental measurements. Finally, we outline strategies for designing hybrid absorbers that can provide application specific low-frequency and broadband absorption performance within specific frequency ranges, while considering engineering constraints on their total mass and depth.

Bioinspired Design of Textile-Based Absorbers: Photothermal and Electrothermal Synergistic Conversion for Efficient Clean-Up of Heavy Oil

Bioinspired Design of Textile-Based Absorbers: Photothermal and Electrothermal Synergistic Conversion for Efficient Clean-Up of Heavy Oil

Silicon nitride-based ultra-wideband ultra-long infrared metamaterial absorber with large angle and high absorption

In the study of mid-infrared band long wavelength infrared (LWIR) has attracted the attention of domestic and foreign researchers due to its great role in medical diagnosis and detection. Broadband absorption is also a key index for metamaterial absorption applications. In this paper, a design of a highly absorbing, large-angle ultra-wideband ultra-long infrared metamaterial absorber based on a single-layer square Si3N4 cavity array and an intermediate layer of Si3N4 thin film, as well as metal Ti as the substrate, is proposed. The ultra-long infrared metamaterial absorber has polarization insensitivity under the condition of positive incidence. Numerical simulations show that the effective absorption bandwidth with more than 90% absorption is 11.12 μm in the band range of 7.65–18.77 μm, in which the average absorption reaches 96.54%. Diffraction and impedance matching induced strong absorption and wide bandwidth. We can adjust the absorption performance by changing the structural size of the absorber. In addition, our design has a very wide operating range of incidence angles, and the TM and TE modes maintain ultra-high average absorption levels under 0°-60° incidence angles, it is worth mentioning that the absorption of the absorber can reach 95.08% at an incident angle of 60°. The absorber design proposed in this paper has a simple structure, the material is easily available and inexpensive, and the fabrication process is very simple, which makes it suitable for infrared imaging, medical detection, and thermoselectronic devices.