High-performance Absorption Research Articles

Multilayer broadband absorber based on gradient impedance difference between layers

Abstract With the rapid advancement of microwave technology, the demand for broadband and high-absorption performance presents significant challenges in the development of microwave materials. To meet these demands, we designed a broadband and high-absorption structure based on the gradient impedance difference between layers, grounded in transmission line theory. Through comparisons of broadband impedance matching and microwave attenuation characteristics under oblique incidence for different polarization modes, the gradient impedance distribution is optimized. Additionally, the relationship between the input impedance of the structure and the free-space wave impedance has been investigated. It is found that the four-layer structure performs the best impedance matching when the interlayer characteristic impedance is 70 Ω. The designed gradient impedance structure achieves a reflection loss of less than −10 dB across the 2–18 GHz frequency range and a stronger reflection loss below −20 dB within the 4.3–18 GHz frequency range. It also maintains a wide incident angle range from 0° to 60° under both transverse electric (TE) and transverse magnetic (TM) polarization modes. This study provides a promising technological approach for the design of broadband and high-absorption structures.

Direct synthesis of bimetallic Co/Zn-MOF-derivative@mica composite with high microwave absorption performance and pearlescent properties

Direct synthesis of bimetallic Co/Zn-MOF-derivative@mica composite with high microwave absorption performance and pearlescent properties

Optimization of parallel coiled cavities of different depths in microperforated panel sound absorbers

This paper presents a microperforated panel (MPP) sound absorber with parallel coiled-up-cavities of different-depths (PCD) and the corresponding optimization on their cavities. In this study, an analytical model is initially proposed for estimating the cavity depths of the PCD-MPP absorber upon normal incidence absorption coefficient evaluation at given resonance frequencies. Cavity effective depths and normal incidence absorption coefficient are evaluated after coiling up cavities for a compact structure. Numerical simulations with the finite element method and experiments are conducted for validations. Subsequently, a design process is suggested on the basis of the proposed model for sound absorption optimization. Results show that, absorption coefficient from the proposed analytical model agrees well with finite element simulations and experiments. It is also shown that, for the effective depth evaluation of the coiled-up cavities of PCD-MPP absorbers, the diagonal lines of subchannels of coiled-up cavities with a coiled-up angle of 180° can accurately represent the effective depths, while the combination of centerlines of subchannels and quarter arc inside the coiled-up area is more suitable for those with a coiled-up angle of 90°. Optimization investigation shows that, PCD-MPP absorbers can have high absorption performance with the averaged and maximum absorption coefficient of 0.91 and 0.98 within the target bandwidth of 400–1600 Hz, where the absorber thickness can stay below 65 mm. This work can provide valuable guidelines for the design of sound absorbers for broadband absorption.

Out-of-plane ordered quaternary (Cr0.5V0.5)4AlC3 MAX phase for high temperature stable electromagnetic wave absorption performance

Out-of-plane ordered quaternary (Cr0.5V0.5)4AlC3 MAX phase for high temperature stable electromagnetic wave absorption performance

All-dielectric metasurfaces enabled by quasi-BIC for high-Q near-perfect light absorption

All-dielectric metasurface (ADM) absorbers driven by quasi-bound states in the continuum (BIC) are critical for high-performance optoelectronic devices due to their ability to offer high Q-factor absorption. However, these all-dielectric metasurfaces usually require the aid of degenerate critical coupling schemes or back-metal reflective layers to achieve high absorption, which often suffers from limitations such as sensitive geometrical parameters, ohmic losses, and low Q-factors. This work presents an ADM for high-Q near-perfect light absorption, which consists of double Si nanorods and SiO2/Ta2O5 multilayers. By breaking the symmetry of the length of the Si nanorods, this ADM can excite a single quasi-BIC resonance corresponding to the electric dipole. Without introducing a metal layer, we realize the highly asymmetric coupling of quasi-BIC by only 6 layers of SiO2/Ta2O5 films. It is theoretically and numerically demonstrated that the quasi-BIC has more than 98% absorption at 943.68 nm and a Q-factor as high as 2842. In addition, the ADM exhibits excellent tolerance to geometrical parameters while ensuring high absorption performance. Our results provide new ideas for the design of all-dielectric perfect absorbers with large tolerances and high Q-factors and also open up new possibilities for optical filtering, optical sensing, and photon detection devices.

Effective Multi-Layered Structure Design with Carbon-Based Hybrid Polymer Nanocomposites Using Evolutionary Algorithms

Electromagnetic wave-absorbing materials (EMAMs) and structures are crucial in aerospace and electronic communications due to their ability to absorb electromagnetic waves. The development of materials that are lightweight, sustainable, and cost-effective, exhibiting high-performance absorption across a broad frequency spectrum, is therefore important. However, homogeneous electromagnetic absorbing materials require assistance to meet all these criteria. Therefore, developing multi-layer absorbing coatings is essential for enhancing performance. The present study uses 21 different composites of varying weight fractions of polypropylene, graphene nanoplatelets, and multiwall carbon nanotubes nanocomposites to develop multi-layer absorbing materials and optimize their performance. These multi-layer carbon polymer nanocomposites were meticulously constructed using evolutionary algorithms like Non-sorted Genetic Algorithm-II and Particle Swarm Optimization to achieve ultra-broadband electromagnetic wave absorption capabilities. Among the designed electromagnetic absorbing materials, a two-layer model, i.e., 1.5 wt% MWCNT/PP/epoxy with a thickness of 1.052 mm and 2.7% GNP/PP/epoxy with a thickness of 4.456 mm totaling 5.506 mm, was identified as optimal using NSGA-II. The structure has exhibited exceptional absorption performance with a minimum reflection loss of −21 dB and a qualified bandwidth extending to 4.2 GHz. PSO validated and optimized this structure, confirming NSGA-II’s efficiency and effectiveness in quickly obtaining optimal solutions. This broadband absorber design combines the structure design and material functioning through additive manufacturing, allowing it to absorb well over a wide frequency range.

Gallium nitride ultra-wideband terahertz absorber based on periodic pyramidal array

Abstract Gallium nitride (GaN) has garnered significant attention due to its unique properties. Here, we present, for the first time, a polarization-independent ultra-wideband absorber in the terahertz band, consisting of a pyramidal GaN array and a GaN substrate. Numerical simulation results indicate that the designed absorber exhibits excellent absorption performance in the range of 0.39 to 1.98 THz, with a center frequency of 1.185 THz. The relative bandwidth ratio is 134.2%, and the absorption exceeds 90%. The equivalent circuit model (ECM) further illustrates the ultra-wideband strong absorption characteristics of the proposed absorber. The simulated electromagnetic field distribution indicates that the perfect absorption of the designed absorber is attributed to the excitation of electromagnetic resonance. Additionally, due to the high structural symmetry, the absorber exhibits polarization-independent properties and maintains high absorption performance at large incidence angles. In the future, this holds great promise for optical applications, including detector devices, photo detection equipment, and solar energy collection systems.

A double-layered optically clear adhesive with enhanced resistance to waviness and impact, designed for use in high-end mobile display

In high-tech display industries, excellent impact resistance and surface waviness implementation technologies have gained much attention as the products are being lightweight and thinned. In particular, as a black pixel defining layer is adopted instead of a polarizer used to prevent external light reflection, impact resistance performance and surface quality characteristics are problematic. Herein, we proposed the double-layered optically clear adhesive (OCA) structure consisting of urethane-acrylate type OCA and UV-curable acrylic OCA for simultaneously achieving impact resistance and surface quality performances. Urethane simultaneously contains the soft segment and the hard segment based on hydrogen bonding between urethane functional groups, indicating high shock absorption performance. In addition, due to this unique structure, it exhibited a high modulus in the compression direction, thereby realizing excellent surface waviness. The UV-curable acrylate OCA can implement basic properties of adhesives such as tacky, adhesion, and inkstep cover capability, while at the same time securing indentation resistance with high modulus after UV curing. Optimization of impact resistance performance and surface waviness according to the thickness and laminating order of the proposed double-layered OCA was performed, and as a result, the double-layered OCA in panel/urethane-acrylate type OCA 100 μm/UV-curable acrylic OCA 25 μm/window structure showed the improved surface quality of 0.22 Kc value improved by 56.8 % and impact resistance of 5.1 cm improved by 100 % compared to the conventional OCA.

A nitrogen-enriched strategy to accelerate the remediation of Cr(VI)-contaminated soil by iron-based materials in microwave fields

The existing remediation technologies for Cr(VI) contamination soil suffer from long processing times. Microwave catalysis is an efficient environmental remediation technology, and the reasonable design of microwave catalysts can enable a microwave catalytic system to rapidly complete the remediation of Cr(VI). In this study, a microwave catalyst, NRFC-3, with high microwave absorption performance and electron density was designed via a nitrogen enrichment strategy. Density functional theory (DFT) calculations verified that the electron density of the material was increased by nitrogen-enriched strategy. Under the experimental conditions, the electrons (e−) of NRFC-3 originate from “hot spots” and the current density is not lower than 3.78 × 109 e·g−1·s−1. In addition, the reduction of Cr(VI) in the MW/NRFC-3 system is feasible through DFT predictions, and this conclusion was experimentally verified. The MW/NRFC-3 system has a remediation efficiency of 100 % for Cr(VI)-contaminated soil within 25 min, significantly reduced the toxicity of Cr(VI) to the environment and humans, and had long-term stability. The potential application of the MW/NRFC-3 system was verified by remediation experiments on Cr(VI)-contaminated soils of different degrees. This study provides a new technology for the rapid and harmless treatment of Cr(VI)-contaminated soil.

Hierarchical meta-porous materials as sound absorbers

The absorption of sound has great significance in many scientific and engineering applications, from room acoustics to noise mitigation. In this context, porous materials have emerged as a viable solution towards high absorption performance and lightweight designs. However, their performance is somewhat limited in the low-frequency regime. Inspired by the concept of recursive patterns over multiple length scales, typical of many natural materials, here, we propose a hierarchical organization of multilayered porous media and investigate their performance in terms of sound absorption. Two types of designs are considered: a hierarchical periodic (HP) and a hierarchical gradient (HG). In both cases, it is found that in some frequency ranges the introduction of multiple levels of hierarchy simultaneously allows for: (i) an increase in the level of absorption compared with the corresponding bulk block of porous material (or to the previous hierarchical levels (HLs)), and (ii) a reduction in the quantity of porous material required. Another advantage of using this approach is on the fabrication, since only one porous material is required. The performances are examined for both normal and oblique incidences, as well as for different values of the static air-flow resistivity. The methodological approach is based on the transfer-matrix method, optimization algorithms such as the metaheuristic greedy randomized adaptive search procedure (GRASP), finite-element calculations and measurements performed in an impedance tube.

The bound states in the continuum of coupled resonance modes and multiple-function applications in grating-cavity structures

The bound states in the continuum (BICs) are desired for high-performance optical devices. The structures composed of gratings and cavities were investigated. Grating waveguide modes (GWMs) are excited by the grating in structures. When the symmetry of the structure is broken, the positive and opposite GWMs couple and generate upper- and lower-coupled modes. Two coupled modes show different properties, such as the Fabry-Pérot (F–P) BIC in lower-coupled mode and the symmetry-protected (SP) BICs in upper-coupled mode. The special properties indicate the two coupled modes are desirable for multifunctional applications. The radiation from the quantum emitter (QE) was enhanced 3030 times through the quasi-BIC of lower-coupled mode. The maximal group delay reached 6.1 ps by the quasi-BIC of the lower-coupled mode. The quasi-BIC of the upper-coupled mode generates high-performance absorption. Two coupled resonance modes are sensitive to polarization, which can be used for optical switching with a maximal amplitude modulation depth of up to 99.8% with an insertion loss of less than 0.008 dB. These results offer hope for developing multifunctional and high-performance devices through coupled resonance modes in the grating-cavity structures.

Synthesis and high electromagnetic wave absorption performance of carbon-enriched porous SiOC ceramics

The carbon-enriched porous SiOC ceramics with enhanced electromagnetic wave (EMW) absorption properties were synthesized through the hydrothermal method followed by a polymer-derived ceramics (PDCs) process. As the annealing temperature rises from 1200 °C to 1500 °C, SiC and SiO2 crystals are gradually separated from the porous amorphous SiOC matrix, and the degree of graphitization of free carbon increases. The porous SiOC ceramics annealed at 1400 °C exhibit the presence of SiC, SiO2, turbostratic graphite, and amorphous SiOC phases, which significantly impact the impedance matching and attenuation constant of the material. The minimum reflection loss (RLmin) value of the SiOC ceramics reaches −67.98 dB with a matching thickness of 3.19 mm and the effective absorption bandwidth (EAB) is 4.45 GHz at 1.39 mm. The carbon-enriched porous SiOC ceramics with strong absorption capacity and wide absorption bandwidth are primarily owing to appropriate impedance matching and multiple attenuation mechanisms, such as conduction loss, interfacial polarization, and defect-induced polarization, indicating that the SiOC ceramics exhibit significant potential as a high-performance EMW absorbing material.

CNTs/lamellar VSe2/Fe3O4 self-assembled a variety of unique three-dimensional multilayer interface structures and microwave absorption properties

Fabrication of microwave absorption (MA) materials of matched small thickness, low density, broad effective absorption bandwidth (EAB), as well as high absorption performance remains a technical challenge to be solved today. In this paper, three-dimensional (3D) VSe2/CNTs/Fe3O4 ternary composites with a variety of self-assembled structures were fabricated by a two-step hydrothermal and one-step carbothermal reduction method. Via varying the content of Fe3O4 in the composites, different 3D multilayer interfacial structures, such as star fruit-, bitter melon-, goldfish-, starfish-, peony- and chrysanthemum-shaped structures were self-assembled, and excellent MA absorption characteristics were obtained. The best reflection loss (RLmin) was −50.96 dB at 1.8 mm thickness. The maximum EAB was 4.93 GHz at 2.0 mm thickness. Carbon nanotubes mainly contributed to conduction and polarization losses. In situ generated VSe2 nanosheets and Fe3O4 nanoparticles promoted the assembly of multilevel interfacial structures, thus contributing to interfacial polarization loss and dipole polarization loss. Fe3O4 also created magnetic losses. This study lays the foundation for fabricating highly efficient MA materials in special self-assembled heterostructures with ternary synergistic effects at the nanoscale.

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•− play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Experimental study on the acoustic properties of monofilament fabrics

The traditional machining perforated sound absorption structure has high processing cost and inconvenient installation and disassembly, so that how to efficiently and economically manufacture submillimeter micropores still remains a challenge. In this study, a kind of flexible microporous sound absorbing material was obtained by weaving a polymer artificial fiber covered with ethylene polyester fiber, and the relationship between the sound absorption performance of the curtain and the porosity of the pass and fabric was obtained through the finite element simulation model and impedance tube experiment. The mechanism parameters of wide-band flexible microporous material with high sound absorption performance are obtained, which guide the design of a kind of sound absorption material with lower production cost and easy installation and disassembly.

Experimental and numerical investigation of soundproof panels using acoustic metamaterials with porous material

Acoustic panels are often used in buildings and automobiles. For sound absorption in panels, high sound absorption performance in a wide frequency band can be achieved by combining porous sound absorption, resonant sound absorption, vibration sound absorption, and acoustic metamaterials. This study proposes a highly sound-absorbing panel structure by using an acoustic metamaterial that generates local resonance to a double-walled structure filled with porous material. In the soundproof panel of this study, local resonance is generated by a structure in which slits are made in a porous material. By the through-holes of the slits, local resonance occurs, but sound leakage and thermal viscosity in the slits may affect the sound absorption effect. Therefore, in this study, sound transmission loss for various cases with differing factors such as the use of porous materials, the presence of spiral slits, and layer configurations are compared through the acoustic analysis and experiments. The results substantiate that the proposed panel structure has high soundproofing performance in wide frequency ranges, each driven by distinct physical principles.

Multi-mode hybridization in the MXene tetramer metasurface for ultra-broadband solar energy utilization

MXene is promising in photothermal or photovoltaic conversion, while high-performance MXene metasurface solar absorbers based on simple and feasible structures are still lacking. This study aims to design a solar absorber with ultra-broadband absorption capability in the visible and near-infrared wavelength ranges based on the MXene nanoblock tetramer/silica film/MXene substrate structure. The average absorptivity of this proposed metasurface absorber is 96.9% in the wavelength range of 300–2500 nm covering the whole solar spectrum. The physics behind the high absorption results from multiple-mode hybridization in different resonant bands, including the coupling between the surface plasmons, cavity resonances, and guided-mode resonances. The broadband and high-absorption performance remains stable under large-angle incidence and structural parameter variations with the average absorption above 90% in the whole wavelength region of interest. The calculated energy absorption ratio of the AM1.5 solar radiation spectrum can reach up to 96.3%, indicating low solar energy loss and efficient solar energy capture. In summary, these results provide great application prospects in the fields of photothermal and photovoltaic conversion.

High-Q all-dielectric metasurface perfect absorber powered by quasi-bound states in the continuum

All-dielectric perfect absorbers powered by quasi-bound states in the continuum (-BIC) are of great importance for developing high-performance optoelectronic devices because they provide high Q-factor absorption. However, these structures usually require the addition of metal back reflectors or degenerate critical coupling to achieve high absorption, which often introduces problems such as Joule heat output and sensitivity to geometrical parameters. In this work, we present an all-dielectric high Q-factor metasurface perfect absorber (MPA) with a cell structure consisting of split Si elliptical disks. By adjusting the tilt angle of the gap, the metasurface can excite a single quasi-BIC resonance in a highly reflective background, corresponding to the electric quadrupole (EQ) mode. Due to the asymmetric coupling of the EQ mode, the proposed metasurface easily breaks the 50% absorption limit. At the wavelength of 894.645 nm, the metasurface achieves a perfect absorption of more than 99% and has a Q-factor of up to 1955. In addition, the structure shows excellent tolerance to geometrical parameters while ensuring high absorption performance. By adjusting the polarization angle, we have also achieved an arbitrary tuning of the absorption efficiency without frequency shift. This work provides a viable scheme for the design of tunable, large-tolerance, and high-Q all-dielectric MPAs, which have a broad potential application in the fields of optical filtering, optical switching, and polarization detection.

High electromagnetic wave absorption performance from all-scale hierarchically defective Ni-Mn-Co-Cu-Al high entropy alloys@carbon

All-scale hierarchical defects induced by structural designing from unit cell to mesoscale play a significant role in oscillating and dissipating electromagnetic wave energy under external microwave radiation. To construct such all-scale hierarchical defects, hereby, high-entropy alloy nanoparticles coated by microscale carbon (HEA@C) with a core–shell structure were obtained by carbonizing Ni-Mn-Co-Cu-Al metal–organic. Thus, all-scale hierarchical defects were gained, including lattice distortion and nanotwins caused by the high entropy effect, vacancy and topological defects within carbon, and the heterojunction between high entropy nanoparticles and carbon. These all-scale hierarchical defects combined with the magnetic and conductive nature of HEA@C enable us to achieve a high electromagnetic wave absorption performance, with a reflection loss (RLmin) value of −52.36 dB and an effective absorption bandwidth (EAB) of 5.01 GHz. It implies that HEA@C should be an effective electromagnetic wave (EMW) absorber.

In Situ Growth of Nitrogen-Doped Fluorescent Carbon Dots on Sisal Fibers: Investigating Their Selective and Enhanced Adsorption Capabilities for Methyl Blue Dye.

Preparing a biomass adsorbent material with high-absorption performance but low cost plays a vital role in wastewater treatment. In this study, a novel nitrogen-doped sisal fiber-based carbon dots (SF-N-CDs) composite was prepared by directly growing carbon dots (CDs) on sisal fiber (SF) using a microwave method with polyethyleneimine (PEI) as a raw material. The prepared SF-N-CDs were characterized using FTIR, XRD, Contact angle(CA), TGA, XPS, and SEM. The results revealed that the CDs were successfully grown on SF. The adsorption properties of SF-N-CDs were significantly enhanced when they adsorbed methyl blue (MeB) dye. Specifically, the adsorption of MeB by SF-N-CDs was up to 619.7mg/g, which was about 2.6 times higher than that of raw SF. This implied that the introduction of CDs increases the adsorption site, thus enhancing the adsorption capacity. Analysis on kinetics and thermodynamics of MeB adsorption by SF-N-CDs revealed that the adsorption process followed the Langmuir isotherm model and were consistent with both kinetic models. It signifies that the adsorption involves both physical and chemical adsorption processes. Further, the SF-N-CDs maintained a removal rate of 70.9% after six adsorption-regeneration cycles, demonstrating good regeneration performance. Moreover, the SF-N-CDs could selectively separate MeB from a mixture of rhodamine B and saffron T. Consequently, the findings of this study suggest that SF-N-CDs are promising adsorbents for anionic dyes.