Stable Absorption Performance Research Articles

Ultra-broadband absorber based on algorithmic optimization of MgF2–Fe stacked structure

Broadband absorbers possess a wide array of potential applications, including electromagnetic cloaking, solar energy harvesting, and solar power generation. However, achieving excellent ultra-broadband absorption with plasma-metal materials remains challenging due to their inherently narrow bandwidth. To tackle this issue, we propose an ultra-broadband absorber, free from lithography, composed of a multilayer stack of magnesium-iron fluoride (MgF2–Fe). In this study, we optimized the structural parameters of the absorber using a particle swarm optimization algorithm to achieve theoretically optimal absorptivity. Numerical simulations revealed that the absorber achieved an impressive theoretical average absorption of 98.4% across a broad wavelength range from ultraviolet to near-infrared (321–1800 nm). Importantly, it exhibited stable absorption performance at large incidence angles (0–70°), while maintaining high absorption efficiency. Furthermore, it demonstrated polarization independence at perpendicular incidence angles. Subsequently, experimental preparations and tests were conducted on absorber samples to evaluate their solar energy absorption capacity. Both experimental and theoretical comparisons underscored the promising potential of this structure for applications in solar energy collection, conversion, and solar power generation.

Polarization independent highly insensitive ultra-wideband absorber for infrared, visible light and ultraviolet region

This work proposes a nickel-dielectric-nickel-based superwideband absorber for the infrared, visible, and ultraviolet spectrums. A square ring is loaded with a corner-truncated square patch to form the resonating structure. The absorber measures 25 × 25 × 10.6 nm3 in total. Absorption (A) is above 90 % throughout a frequency spectrum of 136.3564–5407.291 THz (55.48–2200.12 nm), with an average absorption of 96.49 %. Absorption is ≥95 % within the frequency range of 713.12–4684.15 THz (64.04–420.68 nm). The absorber has A ≥ 80 % for incident angle (θ) ≤ 50°. In the operational band, absorption averages 92.39 % at θ = 50° and 86.65 % at θ = 60°. This absorber has volume reduction upto 99.99 % (in terms of λL3, λL is wavelength at cutoff frequency for A ≥ 90 %), A ≥ 90 % ultrawide bandwidth of ∼190 % (for A ≥ 90 %), average A = 96.49 %, polarization insensitiveness, stable A ≥ 80 % for θ ≤ 50°, almost stable absorption performance for ±0.2 nm dimensions variations due to fabrication tolerances.

Five-Band Tunable Terahertz Metamaterial Absorber Using Two Sets of Different-Sized Graphene-Based Copper-Coin-like Resonators

In this paper, a five-band metamaterial absorber with a tunable function in a terahertz band is proposed, which consists of a gold grounding layer, a polyimide dielectric layer, and a periodic patterned graphene layer. The patterned graphene layer is constructed from two sets of copper-coin-shaped structures of different sizes. The designed absorber achieves absorptions of 96.4%, 99.4%, 99.8%, 98.4%, and 99.9% at 4.62 THz, 7.29 THz, 7.70 THz, 8.19 THz, and 8.93 THz, respectively, with an average absorption intensity of 98.78%. The physical mechanism of this five-band absorber was explained by the impedance matching principle and electric field distribution. The absorption performance of the five-band absorber can be effectively tuned by changing the geometry of the patterned graphene array and the thickness of the dielectric layer. Given that the resonant frequency of the absorber varies in proportion to the Fermi level, by varying the Fermi level of the graphene hypersurface, we can achieve the continuous tuning of the absorption performance over a wide frequency range. The five-band absorber has a stable absorption performance over a wide incidence angle of 0–65°, and by combining the merits of high absorption, dynamic adjustability, and a large number of absorption peaks, the given absorber could have great potential for applications in nondestructive testing, imaging, communication, sensing, and detectors.

Ultra-wideband perfect absorption of MIMI structure based on InSb-Ti

• An MIMI (metal-insulator-metal-insulator) similar multilayer absorber based on the concatenation of Indium Antimonide (InSb) and titanium (Ti) is proposed. • Finite-difference time-domain (FDTD) method is adopted to the MIMI absorption structure. • The structure has stable absorption performance near ultraviolet region (300nm) to part of near infrared region (1200nm). In this paper, a MIMI (metal-insulator-metal-insulator) similar multilayer absorber based on the Indium Antimonide (InSb) and titanium (Ti) is proposed. Finite-difference time-domain (FDTD) method is adopted to give the simulation result. The advised new planar structure (GaF 2 -TiO 2 -InSb-Ti-GaF 2 -Al) achieves ultra-wideband absorption from part near ultraviolet region (300nm) to the part near infrared region (1200nm). As comparing to the MIMI structure based on single transition metal, we have made a progress in expanding the absorption in UV region. The structure also has stable performance, besides insensitive to the changes in the dielectric coefficient of some similar materials, it retains the advantages of MIMI structure's large angle and polarization insensitivity, which further enhances its application potential in solar energy storage and controlled thermal emission.

UWB Frequency-Selective Surface Absorber Based on Graphene Featuring Wide-Angle Stability

In this paper, an ultra-wideband and polarization-insensitive frequency-selective surface absorber is presented with oblique incident stable behavior. Different from conventional absorbers, the absorption behavior is much less deteriorated with the increase in the incidence angle. Two hybrid resonators, which are realized by symmetrical graphene patterns, are employed to obtain the desired broadband and polarization-insensitive absorption performance. The optimal impedance-matching behavior is designed at the oblique incidence of electromagnetic waves, and an equivalent circuit model is used to analyze and facilitate the mechanism of the proposed absorber. The results indicate that the absorber can maintain a stable absorption performance with a fractional bandwidth (FWB) of 136.4% up to 40°. With these performances, the proposed UWB absorber could be more competitive in aerospace applications.

Design and Preparation of Flexible Graphene/Nonwoven Composites with Simultaneous Broadband Absorption and Stable Properties

As the world moves into the 21st century, the complex electromagnetic wave environment is receiving widespread attention due to its impact on human health, suggesting the critical importance of wearable absorbing materials. In this paper, graphene nonwoven (RGO/NW) composites were prepared by diffusely distributing graphene sheets in a polypropylene three-dimensional framework through Hummers' method. Moreover, based on the Jaumann structural material design concept, the RGO/NW composite was designed as a multilayer microwave absorber, with self-recovery capability. It achieves effective absorption (reflection loss of -10 dB) in the 2~18 GHz electromagnetic wave frequency domain, exhibiting a larger bandwidth than that reported in the literature for absorbers of equivalent thickness. In addition, the rationally designed three-layer sample has an electromagnetic wave absorption of over 97% (reflection loss of -15 dB) of the bandwidth over 14 GHz. In addition, due to the physical and chemical stability of graphene and the deformation recovery ability of nonwoven fabric, the absorber also shows good deformation recovery ability and stable absorption performance. This broadband absorption and extreme environmental adaptability make this flexible absorber promising for various applications, especially for personnel wearable devices.

The superhydrophobic sponge decorated with Ni-Co double layered oxides with thiol modification for continuous oil/water separation

In this paper, the superhydrophobic polyurethane sponge (SS-PU) was facilely fabricated by etching with Jones reagent to bind the nanoparticles of Ni-Co double layered oxides (LDOs) on the surface, and following modification with n -dodecyl mercaptan (DDT). This method provides a new strategy to fabricate superhydrophobic PU sponge with a water contact angle of 157° for absorbing oil with low cost and in large scale. It exhibits the strong absorption capacity and highly selective characteristic for various kinds of oils which can be recycled by simple squeezing. Besides, the as-prepared sponge can deal with the floating and underwater oils, indicating its application value in handling oil spills and domestic oily wastewater. The good self-cleaning ability shows the potential to clear the pollutants due to the ultra-low adhesion to water. Especially, the most important point is that the superhydrophobic sponge can continuously and effectively separate the oil/water mixture against the condition of turbulent disturbance by using our designed device system, which exhibit its good superhydrophobicity, strong stability. Furthermore, the SS-PU still maintained stable absorption performance after 150 cycle tests without losing capacity obviously, showing excellent durability in long-term operation and significant potential as an efficient absorbent in large-scale dispose of oily water.

Tunable shell thickness of Fe-N@SiO2 nanoparticles for strong and stable microwave absorption properties with enhanced oxidation resistance

Core-shell composites Fe-N @ SiO 2 with 500 nm average sizes of cores have been successfully prepared by a combination of hydrothermal, gaseous nitriding and Stöber methods. The Fe-N cores are composed of Fe 4 N as major phase and FeN as minority. The thickness of SiO 2 shell increases continuously with increase of the tetraethyl orthosilicate weight. Relative to the natures of Fe-N, Fe-N @ SiO 2 composites show slightly weaker ferromagnetic capacity, but much higher oxidation resistance. The Fe-N sample exhibits extremely high relative permittivity. With filling loading of 50 wt%, it has a moderate microwave absorption performance with a maximum reflection loss about −10 dB. Owing to low conductivity, non-magnetic property and superior anti-oxidation ability of the SiO 2 shell, the core-shell structures have considerably degraded permittivity, and nearly unchanged permeability. These changes bring a much better impedance matching between the permittivity and permeability, and further bring a greatly enhanced microwave absorption performance. All of the Fe-N @ SiO 2 composites have strong absorption abilities. They are quite stable with variation of shell thickness. The composite of 52 nm shell thickness has maximum reflection loss of −23.1 dB at 17.2 GHz, and effective absorption bandwidth (<−10 dB) of 2.4 GHz with absorber thickness 5.5 mm. The present study gives an insight on the roles of silica material influencing the iron-based absorber’s absorption ability. • Fe-N @ SiO 2 nanoparticles with tunable shell thickness were synthesized. • Ferromagnetic Fe-N @ SiO 2 composites have good oxidation resistance. • Core-shell absorbers exhibit strong and stable absorption performance. • Mechanism for SiO 2 modification of absorption performance was revealed.

The tunable single-/narrow-band terahertz metamaterial absorber through photoconductivity

In this work, a photo-excited terahertz metamaterial absorber (PETMA) switched between single-band and narrow-band absorption is reported. Such an absorber includes three layers, which are a metal plate on the bottom, a dielectric layer, and a top unit attached to the dielectric substrate. The upper unit of the proposed PETMA is composed of an innermost ring-shaped and a middle truncated ring-shaped high-impedance surfaces (HISs), a nested split ring-shaped resonator connected with an outer square ring-shaped metal resonator. It is noted that four corners of the square ring-shaped metallic resonator are embedded in photoconducting semiconductors (silicon), respectively. Furthermore, the quadrate air columns (ACs) are inserted in the dielectric substrate to promote the absorption effect of this absorber. The single-band (at 1.16 THz) and the narrow-band absorption (at 1.458–1.538 THz) conversion can be realized through the variation of the conductivity of silicon tuned by an optical pump beam. Besides, the absorption principle of the devised PETMA is analyzed by describing the surface currents, the electric field diagrams, the magnetic field distributions, and the power flow distributions. In addition, the simulations show that the proposed PETMA exhibits stable absorption performance at a wider incident angle.

Enhanced adsorption performance of UiO-66 via modification with functional groups and integration into hydrogels

University of Oslo-66 (UiO-66) was a potential adsorbent for removing various pollutants from wastewater. Modifying the UiO-66 surface with different functional groups could enhance the adsorption performance. In this study, the UiO-66 modified with a functional group of –NH2 or –NO2 was prepared and tested to adsorb different pollutants. The results showed that –NO2 modified UiO-66 increased the adsorption capacity of tetracycline by 17 times to 94.08 mg g−1 compared with unmodified UiO-66. The adsorption process of UiO-66-NO2 followed the pseudo-second-order adsorption kinetic model and Langmuir isotherm model with a maximum isotherm adsorption capacity of 127.32 mg g−1. The adsorption interaction was hydrogen bonding and electrostatic attraction. The UiO-66-NO2 also showed good adsorption performance to Co2+, Methylene blue, Congo red. Fixing UiO-66-NO2 into hydrogel performed a stable absorption performance with a high absorption capacity (71.56 mg g−1) to TC and a good regeneration rate (85%) after five cycles, providing a novel applicable way to remove pollutants from wastewater.

Dual-broadband terahertz absorber based on phase transition characteristics of VO2

A dual-broadband absorption metamaterial based on a composite structure consisting of metal and vanadium dioxide is designed and analyzed. By controlling the temperature of vanadium dioxide, the absorption band of the device can be manipulated. At T = 300 K, before the VO2 phase transition, the designed structure can achieve broadband absorption. Results indicate that the absorption rate can exceed 90% in the broad spectral range of 1.375–2.087THz. In the case of T = 350 K, VO2 transforms into a metallic state, and the absorption band is transferred to 2.6–7.03 THz. Especially, the structure is insensitive to the polarization angle of the incident wave, which is beneficial for maintaining stable absorption performance when the incident angle is less than 45°. The proposed absorber can be applied to many other fields such as modulation devices, terahertz switching, and power harvesting fields.

Dual-band metamaterial absorber with stable absorption performance based on fractal structure

In this paper, two kinds of dual-band metamaterial absorbers (MMAs) with stable absorption performance based on fractal structures are proposed. As the key feature, with the increase in fractal order, the fractal MMAs can reduce the weight while keeping the absorption performance. The multi-band absorption property is analyzed by multiple L-C resonances generated by the fractal structure. By virtue of good impedance matching characteristics and the synergy of the circuit and electromagnetic resonance, effective and stable microwave absorption is readily achieved. Finally, two prototypes are fabricated for demonstration, and the measurement result is consistent well with the simulation one. As expected, the proposed fractal MMAs have the advantage of low-cost, light-weight, and dual-effective absorption bands, and have great potential in the application of multi-band radar stealth.

Lightweight, amphipathic and fire-resistant prGO/MXene spherical beads for rapid elimination of hazardous chemicals

Frequent leaks of hazardous chemicals have a huge impact on human lives, property and the ecological environment. Therefore, the three-dimensional functional porous materials with high absorption efficiency and special wettability for the disposal of hazardous chemical spills is an urgent demand. In this work, a series of spherical beads consisting of partially reduced graphene oxide (prGO) and MXene (Ti3C2Tx) nanosheets were constructed by hydrogen bond induced self-assembly along with freeze-drying and thermal treatment. The lightweight and amphipathic prGO/MXene spherical beads (prGMSBDs) had millimeter-level size, spherical morphology and highly porous internal structure, which were especially suitable for eliminating hazardous chemicals. Because of their excellent thermal stability and fire retardance, the prGMSBDs could be used to absorb flammable organic liquids, reducing the fire risk of the flammable hazardous chemical spills. Indeed, the prGMSBDs exhibited outstanding absorption performances for various hazardous chemicals, including organic solvents and water-based concentrated acid and alkali. Moreover, the prGMSBDs showed relatively stable absorption performance after five absorption-drying cycles. Due to meeting the requirements of both amphipathic characteristic and flame retardancy, the prGMSBDs reported in this work may offer a promising strategy for rapidly cleaning up various hazardous chemicals and open a feasible route to protecting the combustible hazardous chemical spills from fire.

A Green Approach to Modify Surface Properties of Polyurethane Foam for Enhanced Oil Absorption.

The non-selective property of conventional polyurethane (PU) foam tends to lower its oil absorption efficiency. To address this issue, we modified the surface properties of PU foam using a rapid solvent-free surface functionalization approach based on the chemical vapor deposition (CVD) method to establish an extremely thin yet uniform coating layer to improve foam performance. The PU foam was respectively functionalized using different monomers, i.e., perfluorodecyl acrylate (PFDA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), and hexamethyldisiloxane (HMDSO), and the effect of deposition times (1, 5 and 10 min) on the properties of foam was investigated. The results showed that all the modified foams demonstrated a much higher water contact angle (i.e., greater hydrophobicity) and greater absorption capacities compared to the control PU foam. This is due to the presence of specific functional groups, e.g., fluorine (F) and silane (Si) in the modified PU foams. Of all, the PU/PHFBAi foam exhibited the highest absorption capacities, recording 66.68, 58.15, 53.70, and 58.38 g/g for chloroform, acetone, cyclohexane, and edible oil, respectively. These values were 39.19–119.31% higher than that of control foam. The promising performance of the PU/PHFBAi foam is due to the improved surface hydrophobicity attributed to the original perfluoroalkyl moieties of the HFBA monomer. The PU/PHFBAi foam also demonstrated a much more stable absorption performance compared to the control foam when both samples were reused for up to 10 cycles. This clearly indicates the positive impact of the proposed functionalization method in improving PU properties for oil absorption processes.

Ultrathin, polarization-insensitive multi-band absorbers based on graphene metasurface with THz sensing application

This article presents multi-band plasmonic absorbers based on a graphene array at terahertz frequencies. The absorbers are made of a very simple structure including a graphene disk array printed on the top surface of a dielectric spacer backed by a metallic ground plane. Multi-band performance is achieved with more than 90% absorption in the 1–8 THz frequency range by exciting surface plasmon polaritons of graphene. It is shown that the resonance frequencies of the proposed absorber can be tuned by varying the chemical potential between 0.8–1 eV for a triple-band absorber and 0.7–0.9 eV for a quad-band one, while keeping more than 80% absorption. The results obtained by means of full-wave simulation are verified with the results obtained by the analytical circuit model. The proposed absorbers are polarization-insensitive and provide stable absorption performance for both of the TE and TM polarizations. As an application, we designed a refractive index sensor based on the triple-band absorber. The results verify that the absorption bands are sensitive to the variations of the refractive index of the coating layer.

Broadband radar absorbing sandwich composite with stable absorption performance for oblique incidence and its application to an engine duct for RCS reduction

In this study, a broadband radar absorbing sandwich composite (BRASC) with stable absorption performance for oblique incidence is proposed to reduce radar cross-section (RCS) of an engine inlet. To design the BRASC, the objective function for broadband absorption performance is coupled with transmission line theory. The absorption bandwidth of the designed BRASC with a − 10 dB criterion is 8.2 GHz. The absorption performance of the oblique incidence in both transverse electric and transverse magnetic polarizations is excellent in maintaining the −10 dB up to 60°. The measurement results of the fabricated specimens confirm that the overall tendency of the measurement results matches well with the analysis results. The engine duct replaced with the BRASC is analyzed to confirm the effect of RCS reduction on the engine inlet. RCS simulation shows that the proposed BRASC effectively reduces the RCS over a wide frequency range. Because the S-shaped duct, which is used in low observable aircraft for RCS reduction, causes multiple scattering at oblique incidence, the absorbers applied to the engine duct should maintain a stable oblique incidence performance. Hence, the proposed BRASC may be a promising candidate for engine inlets with small RCS.

Efficient and stable thin-film crystalline silicon solar cell by introducing rotation factor in surface square pillar array grating

To obtain efficient and stable light trapping, angle rotation is introduced to form rotated square pillar array grating (SPAG) solar cells. Compared with the unpatterned stack slab and the optimized uniform SPAG cells, the maximum short-circuit current ( J sc) of the optimized rotated SPAG is increased by 78.54% and 3.21%, respectively. Moreover, besides the fact that the low-incidence angular sensitivity of J sc could be maintained, J sc of the optimized rotated SPAG will always be larger than that of the optimized uniform SPAG at any incident angle. Furthermore, when the structural parameters of the subsquare pillar slightly deviate from the optimum, the absorption only deceases slightly as well, which indicates both a high structural tolerance and a stable absorption performance. In addition, our results show not only that the proposed rotated SPAG is promising to make light trapping efficient and stable but also that introducing rotation disorders is promising for other high-absorption pseudounordered surface structures.

Facile fabrication of superhydrophobic polyurethane sponge towards oil-water separation with exceptional flame-retardant performance

In this article, a superhydrophobic polyurethane (PU) sponge with exceptional flame-retardant property, was fabricated by coating polydopamine (PDA) through one-step polymerization and surface treatment with hexamethyl disilazane (HMDS). Specifically, dopamine was polymerized in an alkaline solution to generate PDA nano-aggregates as hierarchically rough structure on PU sponge skeleton. After the sponge was further treated with HMDS, the obtained PU-PDA-HMDS sponge surface was transformed from hydrophilic into superhydrophobic with a water contact angle about 153°. The Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurement results demonstrated that the PDA nano-aggregates layer was successfully coated onto PU skeleton, and HMDS molecules were grafted onto PDA nano-aggregates layer by forming silicyl groups on sponge. When the superhydrophobic PU-PDA-HMDS sponge was used towards oil-water separation, it exhibited high oil absorption capacity and stable absorption performance even after cyclic absorption-desorption process. Meanwhile, the sponge exhibited good elastic property and recovery ability under compression test. Furthermore, the thermal stability and flame-retardant property of the sponges were measured, and the results showed the resulting PU-PDA-HMDS sponge exhibited superior thermal stability and flame-retardant property to the pristine PU or PU coated with PDA alone. Even encountering a flame attack, the PU-PDA-HMDS sponge would be self-extinguished and remained its structure integrity due to the formation of silica-hybrid char residue layer during combustion process. The formation process of silica-hybrid char residue layer and what role it exerted on enhancing flame-retardant property were proposed and discussed. Therefore, this work not only provided a simple strategy for fabricating the superhydrophobic porous composites for oil-water separation, but also opened a door to protect the combustible porous composites from fire with exceptional flame-retardant performance.

Enhanced CO2 capture by binary systems of pyridinium-based ionic liquids and porous ZIF-8 particles

Abstract Absorption and adsorption technology as widely used methods have been reported for carbon dioxide (CO2) separation. In order to combine the advantages of absorption and adsorption methods, ionic liquids (ILs) as absorption function and zeolitic imidazolate framework-8 (ZIF-8) as adsorption function were integrated into a slurry to efficiently capture CO2 by the absorption-adsorption method. In this study, two pyridinium-based ILs, [C4Py][NTf2] and [C4Py][N(CN)2] were synthesized, and mixed with different concentration of ZIF-8 to form hybrid slurries. CO2 solubility in the different hybrid slurries at temperatures from 303.15 to 333.15 K was measured. The results indicated that CO2 solubility increases significantly with increasing pressure and decreases with increasing temperature. Moreover, CO2 solubility increases with the increase of ZIF-8 content, indicating that the addition of ZIF-8 into ILs can obviously enhance CO2 solubility. CO2 solubility in the ZIF-8/[C4Py][NTf2] slurry increases by 24% compared with the corresponding pure IL at 303.15 K and 1.80 MPa. The absorption-adsorption mechanism was studied using FT-IR and NMR spectroscopy. It was demonstrated that CO2 absorption and adsorption in the ZIF-8/ILs hybrid slurries is a physical process. Furthermore, the ZIF-8/[C4Py][NTf2] slurry can also keep the stable absorption performance after five consecutive absorption and desorption cycles. Considering the excellent capacity, thermal stability and recyclability, the porous materials/ILs slurry will provide new insight to CO2 capture compared with the conventional absorbents.

A thin hybrid circuit-analog (CA) microwave absorbing double-slab composite structure

In this study, a thin hybrid circuit-analog (CA) microwave absorbing double slab composite structure is presented. Unlike conventional CA absorbers, the composite spacer in the proposed structure is made up of a glass/epoxy and high permittivity layer of glass/epoxy-MWCNT composite, which contributes to the stable absorption performance in the curved surface while maintaining the thin thickness of the composite spacer. To design the microwave absorber, the genetic algorithm which is the most used evolutionary algorithm technique in this field was used. The total thickness of the designed double slab CA absorber was very thin thickness of 2.37mm. Although the designed absorber has very thin thickness, it could satisfy the −10dB absorption in whole X-band (8.2–12.4GHz). The absorbing performance of the designed absorber was compared with other types of absorber. Also, to check the absorbing performance of the proposed structure in the curved surface, the echo radar cross section (RCS) was simulated in the X-band with other types of absorber. The simulated results proved an excellent performance of a proposed novel double slab CA absorber.