Composition Absorption Research Articles

The development of sound absorber material from green composites

One of the most critical parts of ship structure is the sound absorber on the ship structure, particularly in the ship’s engine room, which is a dominant contributor to ship noise. The development of sound absorber materials from natural fibre composite is becoming more varied as material technology develops. This study investigated the sound absorber and thermal conductivity performances of developed sound absorber material. This study used the two-microphone impedance tube method to compare the effectiveness of composite sound absorbers made from three different compositions of water hyacinth fibre, coconut fibre, and sengon wood powder. The coefficient of sound absorption (α), transmission loss, noise reduction, and thermal conductivity (λ) values of three different material compositions become parameters to measure the efficiency of the developed material. The results show that Specimen A (20% hyacinth fibre, 15% coconut fibre, 15% sengon wood) has the highest sound absorption coefficient of 0.57, with stable transmission loss and noise reduction values. The optimum thermal conductivity is found in Specimen C, with the lowest thermal conductivity value.

Design and preparation of double-layer iron ore tailings cement-based electromagnetic wave absorbing materials containing carbon black and steel fiber

Double-layer iron ore tailings (IOTs) cement-based electromagnetic wave (EMW) absorbing materials with carbon black (CB) and steel fiber (SF) were designed, fabricated, and used as composite absorbers, including matching and absorbing layers. The effects of IOTs, CB, and SF on the mechanical properties and electrical conductivity of cement mortar are studied. The EMW absorbing properties and mechanism allowing IOTs cement mortar to cooperate with CB and SF are also examined in terms of loss attenuation and impedance-matching characteristics. Based on the design of a single-layer structure, the optimal mix proportion and layer thickness for the double-layer structure are determined by following the principle of gradual impedance design. The results showed that the EMW absorbing properties were significantly influenced by loss attenuation and impedance matching. When the thickness of the single-layer structure was 10 mm, the minimum reflection loss (RL) reached −25.73 dB with an effective bandwidth of 0.39 GHz. In contrast, the double-layer structure exhibited excellent broadband. When the thickness of the matching layer was 5 mm and those of the absorption layer was 5 mm and 10 mm, the minimum RL of the double-layer structure reached −38.38 dB and −26.51 dB, with ultra-high effective bandwidths of 2.15 GHz and 2.29 GHz, respectively. Thus, double-layer EMW absorbing materials have excellent absorbing properties and exhibit considerable design flexibility and diversity, and may be considered suitable candidates for preparing promising EMW cement-based materials.

Fabrication of CuS/Fe3O4@polypyrrole flower-like composites for excellent electromagnetic wave absorption

Recently, electromagnetic radiation is a serious threat to equipment accuracy, military safety and human health. The combination with different materials to fabricate absorber composites with well-designed morphology is expected to ameliorate this issue. In here, CuS/Fe3O4@polypyrrole (CuS/Fe3O4@PPy) flower-like composites are constructed by the combination of hydrothermal method, solvothermal method and in-situ polymerization. CuS with flower-like structure consisting of nanosheets can provide a conductive backbone and large specific surface area. Hollow Fe3O4 microspheres play a key role in deciding magnetic loss, and electromagnetic waves can penetrate their hollow structure, result in multiple reflection and refraction. PPy coating can enhance the combined strength of composite, and effectively consume microwaves by scattering and multiple refraction in the intercalated structure. As expected, the minimum reflection loss (RLmin) of CuS/Fe3O4@PPy composites is −74.12 dB at 8.16 GHz with a thickness of 2.96 mm, and the effective absorption bandwidth (EAB) is 4.6 GHz (13.4–18.0 GHz) at 1.68 mm. The excellent electromagnetic wave absorption performances are attributed to the synergy effect of different components. This work provides a unique strategy for the structural design of flower-like microspheres in the field of electromagnetic wave absorption.

MOFs derived Fe/Co/C heterogeneous composite absorbers for efficient microwave absorption

Microwave absorbing materials (MAMs) can effectively attenuate microwave energy and avoid the secondary pollution of microwaves, showing great research significance. However, most of the reported MAMs are short of efficient electromagnetic wave absorption ability in low-frequency microbands (such as S-band in 2–4 GHz). Herein, we proposed a "MOF on MOF" design to obtain a Fe/Co/C multicomponent composite through the synthesis of ion-ligand of two MOFs and subsequent high-temperature pyrolysis, realizing the broadband microwave absorption(MA) and superb electromagnetic wave absorption in S band. ZIF-67 was grown in situ on micron-scale spindle NH2-MIL-88B (Fe) as the bearing matrix to obtain the precursor composed of Fe-MOF and Co-MOF. After pyrolysis at high temperature in an inert atmosphere, the organic components are carbonized to form a carbon layer coated with magnetic nanoparticles composed of Fe and Co. The characteristics of a rich heterogeneous interface and large specific surface area enhance the polarization ability of composite absorbent and the conduction dissipation path of electromagnetic wave. Besides, the composite absorbent can cover the absorption demand of 2–18 GHz with an adjustable thickness. We believe that this composite design of multiple MOFs can provide a new reference for the realization of efficient microwave absorption.

Optimization of magnetite with modified graphene for microwave absorption properties

Nowadays, the demand for microwave absorption materials (MAMs) is intensifying in response to the rising sensitivity of electromagnetic pollution and the need for contemporary military security. Therefore it is crucial to develop outstanding performance MAMs. In this study, magnetite-modified graphene (MMG) was synthesized using the solvothermal method by varying the amount of magnetite with graphene nanoplatelets. Later, to optimize the best-suited proportion at which maximum microwave absorption properties were achieved. The structural morphology, phase crystallinity, and chemical composition of the MMG composites were investigated. The morphology reveals that magnetite particles are firmly attached to the edges of the graphene nanoplatelets (GNP). For the microwave absorption investigation, the permittivity, permeability, and reflection loss values of the composite absorbers were measured with a vector network analyzer. The reflection loss of the MMG with a low filler proportion reaches -56.64 dB at a frequency 11.7 GHz and bandwidth 2.16 GHz at a thickness of 3 mm. The sample (3–7) was most suitable for good microwave absorption properties.

Implied Open‐circuit Voltage Imaging via a Single Bandpass Filter Method—Its First Application in Perovskite Solar Cells

AbstractA novel, camera‐based method for direct implied open‐circuit voltage (iVOC) imaging via the use of a single bandpass filter (s‐BPF) is developed for large‐area photovoltaic solar cells and precursors. The photoluminescence (PL) emission is imaged using a narrow BPF with centre energy inside the high‐energy tail of the PL emission, utilising the close‐to‐unity and nearly constant absorptivity of typical photovoltaic devices in this energy range. As a result, the exact value of the sample's absorptivity within the BPF transmission band is not required. The use of an s‐BPF enables a fully contactless approach to calibrate the absolute PL photon flux for spectrally integrated detectors, including cameras. The method eliminates the need for knowledge of the imaging system spectral response. Through an appropriate choice of the BPF centre energy, a range of absorber compositions or a single absorber with different surface morphologies, such as planar and textured, can be imaged, all without the need for additional detection optics. The feasibility of this s‐BPF method is first validated. The relative error in iVOC is determined to be ≤1.5%. The method is then demonstrated on device stacks with two different perovskite compositions commonly used in single‐junction and monolithic tandem solar cells.

Composite structure design of a broadband metamaterial absorber based on magnetic composites

The requirements for electromagnetic wave absorbing materials are increasing as modern technology advances. However, traditional absorbing materials have limitations due to their thickness and incompatibility with high and low frequencies, and metamaterial absorbers have limitations due to their narrow effective absorption bandwidth. This paper overcomes these problems and designs and prepares a broadband, thin and light metamaterial absorber. The effective absorption bandwidth of the composite structure metamaterial absorber (CSMMA) with a thickness d1 of 3 mm reaches 11.55 GHz with the addition of FeSiBPCuY5p/paraffin magnetic composite into the metamaterial absorber and the optimization of the structural parameters. The composite structure design greatly improves the absorption performance of the metamaterial absorber. The advantages of the tunable frequency absorption characteristics of the metamaterial absorber and the high-frequency broadband absorption performance of the magnetic wave absorbing materials are fully exploited in the design of the absorber. Which is of great significance for the development of broadband and thin-absorbing materials. This absorber can be adapted to meet the needs of practical applications by adjusting its structural design, expanding its range of applications and having a substantial influence on the use of wave absorbing materials.

Preparation of Ni/C composite microwave absorbers with high performance by controlling nickel source

Three Ni/C composites with different morphologies were prepared by changing nickel salt using a hydrothermal method and high-temperature pyrolysis. Results show that material defects, nitrogen doping, heterointerface, conductive network, and magnetic effect optimize impedance matching, resulting in the synergistic effect of conductivity loss, polarization loss, multiple scattering, and magnetic loss. The reflection loss of the sample prepared using nickel nitrate is − 44.2 dB at 11.84 GHz and 2.4 mm thickness, and the effective absorption bandwidth is 5.2 GHz. In addition, radar cross section simulation demonstrates the excellent performance of the material in practical applications. Thus, the sample prepared using nickel nitrate is a candidate material for radar stealth and electromagnetic wave absorption.

Tunable high-performance microwave absorption of cobalt nanoparticles wrapped in N-self-doped carbon nanofibers at ultralow filler loadings

Manufacturing lightweight, ultralow filler loading, broad bandwidth and highly efficient microwave absorbers is still a challenge. Herein, we have synthesized Co nanoparticles decorated N-self-doped carbon nanofibers (Co@NCNFs) composite by electrospinning followed by a two-step heat treatment and investigated its electromagnetic (EM) and microwave absorption performances under different filler contents (from 2.5 to 7.5 wt%) in paraffin wax matrix. It is found that the Co@NCNFs composite has strong ferromagnetism and moderate graphitization degree as well as abundant polar groups and defects, and Co nanoparticles encapsulated by graphitic carbon layers with sizes around 45–115 nm are uniformly dispersed in the NCNFs. With increasing the filler loading, the EM attenuation ability is gradually strengthened while the impedance matching level is just the opposite. The EM absorbing properties of the composites are more superior within 5.0 wt% Co@NCNFs loading owing to the synergy of improved impedance matching and satisfactory EM dissipation ability. Under an ultralow filler loading of 2.5 wt%, the optimal reflection loss (RL) can reach as strong as −49.3 dB at 17.83 GHz with a thin thickness of 1.61 mm and the maximum effective absorption bandwidth (EAB, RL<−10.0 dB) is as wide as 5.44 GHz (12.56–16.99 GHz) at 1.92 mm. When the filler loading is only 5.0 wt%, a minimum RL value of −52.3 dB is achieved at 6.36 GHz with the thickness of 3.03 mm and the maximum EAB is 4.64 GHz (13.36–18.00 GHz) at 1.42 mm. Compared to other Co/C composite absorbers, the as-prepared Co@NCNFs composite with well-designed constitute and structure demonstrates the better comprehensive absorption performance at a much lower filler loading. Therefore, the present Co@NCNFs may be more promising for practical applications as lightweight and high-performance EM wave absorbers especially in the medium and high frequency range.

In situ-derived carbon nanotubes decorated the surface of CoxNiy@C composites from MOFs for efficient electromagnetic wave absorption

The in situ formation of interconnected carbon nanotubes (CNTs) networks on the surfaces of metal-organic framework (MOF) derivatives is an efficient method for rationally constructing heterogeneous interfaces and developing high-performance electromagnetic wave absorption materials. A series of CoxNiy @C composite absorbers with abundant CNTs on their surfaces prepared by pyrolyzing MOF precursors in an Ar atmosphere is reported in this study. The S-3 composite absorber had a distinct structural morphology, and optimal wave absorption performance was obtained when the final pyrolysis temperature was 800 °C. At matched thicknesses of 2.0 mm and 3.5 mm, an effective absorption bandwidth (EAB) of 4.5 GHz and a minimum reflection loss (RLmin) of −43.5 dB were achieved when the absorber filling ratio was 15 wt%. This strategy and the results reported in this study are anticipated to encourage future studies into the controlled growth of metal-catalyzed CNTs and inspire new ideas for designing and preparing enhanced microwave absorber materials at the micro-nano scale.

Synergistic polarization loss of binary metal selenides for enhancing electromagnetic wave absorption

The development of multi-component dielectric composites has become the major method to obtain excellent electromagnetic wave (EMW) absorbing materials. However, traditional ways of component introduction are often complicated and uncontrollable, and lack the regulation of components, interfaces and defects. In this paper, the Mo-based binary metal selenides (Mo-M selenides) with flower-like hollow structure was prepared controllably by introducing competing ions during the preparation of MoSe2. By changing the concentration and species of competing ions to regulate the composition, defects and interface, the electromagnetic wave absorption performance of Mo-M selenide can be adjusted. Multiple components, rich heterointerfaces and defects achieved perfect impedance matching and multiple polarization loss, improving the EMW absorption performance. The minimum reflection loss (RLmin) of Mo-Fe(0.08) selenides reached − 60.4 GHz, and the effective absorption bandwidth (EAB) covered the entire X-band at 2.9 mm. Moreover, the EAB of Mo-Fe(0.12) selenides at 1.9 mm was 5.9 GHz, covering almost the entire Ku-band. Other Mo-M selenides also exhibited excellent EMW absorption properties. This work not only proposed a new idea to study the comprehensive effects of interfaces, components, and defects on electromagnetic wave absorption, but also provided a simple and controllable method for constructing efficient composite absorbers.

Preparation of a Flexible X-Band Radar-Wave-Absorbing Composite Material by Using Beta-Silicon Carbide and Polyurethane as Substrates and Multiwalled Carbon Nanotubes as Additives

Silicon carbide (SiC) has good chemical resistance, excellent mechanical properties, thermal conductivity, especially in extreme conditions of application, and has proved to be a very promising electromagnetic absorption material. However, single silicon carbide cannot meet the increasing demand for high performance of absorbing materials. It has become an important research direction to combine it with other absorbing materials to improve its absorbing performance. In this study, a composite absorber material was prepared by 50 wt.% micron-sized beta-silicon carbide (β-sic) powder, mixed with a 0.2 wt.% multiwalled carbon nanotubes (MWCNTs) and 50 wt.% polyurethane (PU) substrate. The mixture was stirred and deaerated to form a slurry, and sprayed onto synthetic fabric. The results showed that the composite material was flexible, with a thickness of less than 2 mm and favorable adhesion. The results obtained by reflection graph of the radar waves, indicated that the return loss within the X-band range (8–12 GHz) was less than −40 dB, indicating favorable radar wave absorption. Therefore, composite materials could thus be used successfully as radar wave absorbers, and was suitable for stealth materials in “asymmetric warfare”.

Design of Melamine Foam/perforated Plates Composite Absorber for Effective Sound Absorption Performance

To give full play to the advantages of perforated plate backed by porous materials in low and medium frequency noise absorption, this study uses Johnson-Champoux-Allard method with the finite element model to describe the acoustic characteristics of this composite structure. The effects of structural parameters of perforated plate and characteristic parameters of melamine foam on sound absorption coefficient were systematically investigated by numerical simulation. Practical composite were prepared to verify the reliability of the numerical simulation method. The simulation and experimental data in this study are helpful to promote the design of porous material-perforated plate structure for noise control in life.

Microwave absorbing properties of polyaniline coated Buckypaper reinforced epoxy resin composites

AbstractWith the development of science and technology and electronic industry, electromagnetic wave pollution has become the fifth largest pollution in the world today, so it is very important to develop a material with good wave absorbing properties. In this study, polyaniline was loaded onto the surface of carbon nanotubes (CNTs) bundles in Buckypaper by electropolymerization, and epoxy resin was used as the matrix to prepare a polyaniline (PANI)/Buckypaper/EP composite absorber with integrated structure and function. The research shows that the CNTs are prepared into Buckypaper with a three‐dimensional porous structure by vacuum filtration. This three‐dimensional porous structure ensures that CNTs can be added at a high content and uniformly dispersed in epoxy resin. PANI adjusts the impedance matching of Buckypaper and adds more loss mechanisms. Under the optimal matching thickness of 1.5 mm, the optimal reflection loss reaches −29.31 dB, and the absorption bandwidth is 3.12 GHz. At the same time, the interaction between the π–π noncovalent bond of PANI and the delocalized π electrons on the surface of CNTs improves the mechanical strength of Buckypaper. The tensile strength reached 42.17 MPa, an increase of 92.82% compared with pure BP/EP. The research in this article is expected to provide a feasible idea for the preparation of structure–function integrated materials.

Tunable and ultraefficient microwave absorptivity in SnO2/Sn/rGO composites via enhanced polarization effect

Absorbing materials featuring effective frequency modulation are expected to meet the requirements for practical application, but remain a significant challenge. To this end, a high efficiency and absorption-range electromagnetic wave absorber was hereby proposed, and a series of rGO-based composites and the realization of effective frequency modulation in 8–14 GHz (<−10 dB) were successfully obtained by controlling the interface components (SnO2/Sn). This ascribes to the adjustable relaxation polarization, which plays a decisive role in microwave loss and the frequency modulation mechanisms. Besides the ideal regulation range of relaxation polarization for dielectric loss materials was confirmed (0.09–3.1) by conforming to the optimal impedance matching principle. In addition, the Sn/rGO and paraffin composite absorbers with reflection loss values of − 39.5 dB at 3 mm were obtained in X-band (5 wt%). The enhanced polarization loss and microwave absorptivity can be explained in terms of the intrinsic carrier concentration and the carrier migration. Overall, the hereby proposed strategy and theoretical analysis do provide a new perspective for designing absorbing devices in practical application.

Experimental study of the core role of GFRP and LDPE on the collapse behavior of absorbers printed with PLA and ABS

Since the advent of polymeric materials, many structures have always been built for engineering purposes. On the one hand, the emergence of composites containing glass fibers has had a significant impact on reducing the weight of structures in various industries. On the other hand, with the advent of 3D printers, many limitations for the geometry of engineering structures were removed. In this research, due to the wide application of these two sciences, a new type of composite absorbers has been introduced. The presented absorbers have glass fiber-reinforced polymer cores (GFRP) or low-density polyethylene cores (LDPE), the shells of each sample are made of PLA or ABS. In this study, 24 different samples were tested under quasi-static loading. The samples were examined in three different groups. In the first group, no cores were used, but in the second group, GFRP cores were used, and in the third group, LDPE cores were used. Triangular, trapezoidal, semielliptical, and square sections were studied, and the results showed that the lowest maximum force was related to samples with semielliptical cross section, then the maximum force increased by changing the cross section from triangular to trapezoidal and then to a square. In addition, the maximum force was higher in the GFRP core than in the LPDE core.

Heterogeneous N-doped carbon composite NiSe2–FeSe double-shell hollow nanorods for tunable and high-efficient microwave attenuation

To develop high-performance microwave absorbing materials, a heterogeneous NiSe2–FeSe@NC double-shelled hollow nanorods (NiSe2–FeSe@NC DSHNs) is constructed based on the strategies of morphology structure optimization and multicomponent recombination. First, NiSe2–FeSe DSHNs are prepared through the cation exchange of Fe-based MOFs and subsequent selenization process. After that, the surface is coated with polydopamine (PDA) and annealed at high temperature to obtain NiSe2–FeSe@NC DSHNs composite absorber. By changing the addition amount of DA, the microstructure, magnetic content and N doped carbon content of the material are effectively optimized. The minimum reflection loss (RLmin) of designed optimal NiSe2–FeSe@NC DSHNs reaches −52.84 dB, and the overall effective absorption bandwidth (EAB, RL < −10 dB) covers 14.1 GHz (3.9–18 GHz). The maximum EAB at 1.7 mm is 4.5 GHz (13.1–17.6 GHz). The excellent microwave absorption (MA) performance is mainly attributed to the enhanced dielectric loss capability and optimized impedance matching, which are supported by the unique double-shell hollow structure, abundant channels and heterointerfaces, complementary magnetic/dielectric compositions, and suitable N heteroatom doping. The investigation of this work provides a convenient and environmentally friendly way for the construction of double-shell hollow structures, and provides a new idea for the design and preparation of lightweight and efficient absorbing materials.

Bioinspired moth-eye multi-mechanism composite ultra-wideband microwave absorber based on the graphite powder

Broadband electromagnetic wave absorbers are of great significance in military and civil fields. Absorbent coatings, although highly conformal, suffer from a narrow absorption band and a single absorption mechanism. In this work, inspired by the idea of bionics, we extracted the structural model of the moth-eye and designed the structure size by using electromagnetic simulation. Conductive graphite powder was selected as the wave absorbing agent due to its good dielectric and conductivity losses, and the final products were prepared according to the structural parameters obtained from the simulation. The result shows that the frequency bandwidth with absorption rate above 90% (reflection loss < −10 dB) of the products could reach 13 GHz, including C, X and Ku bands. The equivalent electromagnetic parameters of the bionic structure absorber were extracted by the inversion method, and its impedance gradient absorption mechanism was revealed by combining with the transmission line theory. In order to optimize low frequency (S-band) absorption, the introduction of Salisbury screen and bionic structure absorber combinations to form a composite absorber, the low-frequency absorption performance is effectively improved. The work shows that the combination of two absorption mechanisms, impedance gradient and interference, could effectively improve the absorption bandwidth of electromagnetic waves, providing a good idea for the design of the carbon-based broadband absorber.

Enhancing sound absorption for an acoustic metastructure with extended tubes at ultra-low frequency

A micro-perforated plate (MPP) as a typical acoustic absorber has ideal sound absorption performance at mid-frequency. A novel metastructure with a MPP and multiple sub-cavities (MPP-MSC) is proposed to broaden the sound absorption frequency range based on Helmholtz resonance, and its sound absorption performance is studied theoretically, numerically, and experimentally. Then, the genetic algorithm is adopted to extend the effective sound absorption band by 120 Hz and reduce the structure thickness to less than 61 mm, which is about 40% thinner than the existing structures. Additionally, a perforated plate with extended tubes (PPET) and porous sound absorptive material (PSAM) are introduced into the metastructure to enhance sound absorption performance in the ultra-low and mid-frequency range. Therefore, the composite sound absorber (PP-MPP-MSC) composed of PPET, PSAM, and MPP with superior sound absorption performance is proposed. Specifically, the effective acoustic absorption frequency of the structure can be broadened to 200–1800 Hz with a maximum thickness of 61 mm. It is worth noting that the design and fabrication of PP-MPP-MSC are relatively accessible, and effective sound absorption performance can be achieved in a certain frequency range, which presents the guiding role for current noise reduction applications.

Mosquito's eyes inspired, hydrophobic and multifunctional coating on flexible polyurethane (PU) foam: highly efficient oil spills remediation and exceptional flame-retardant performance

Inspired by the structure of mosquito's compound eyes, a hydrophobic flexible polyurethane (PU) foam composite (named as PU@SiO2/ADP) with good flame-retardant property was fabricated by coating aluminum diethylhypophosphite (ADP) and in situ-formed SiO2 nanoparticles. Owning to considerable surface roughness of stacked SiO2 nanoparticles and intrinsic hydrophobicity of ADP, the water contact angle (WCA) of modified PU foam increased from 113° to 133°. The absorption capacity of modified foam to oils and organic solvents was also evaluated. The results showed that the absorption ratios of the modified PU to dichloromethane reached 69 g/g. The oil-water separation results proved that PU@SiO2/ADP foam could rapidly and selectively absorb oils or organic solvents from the water surface even under turbulent flow conditions. Fabricated hydrophobic PU maintained excellent oil absorption properties after 10 absorption-squeezing cycles, demonstrating good recyclability. The modified PU foam also showed high flame retardancy. The surface treatment method applied in this research not only provides an effective strategy for fabricating a promising absorbent PU foam for oil spill treatment, but also brings a promising prospect for enhancing the flame-retardant performance of these absorbent polymer composites. This work provides support and reference for the improvement of similar materials in future works.