Excellent Sound Absorption Research Articles

Sound absorption and thermal insulation performance of sustainable fruit stone panels

The sound absorption and thermal insulation behavior of panels made of different fruit stones, including peach, apricot, plum, date, and black cherry, were investigated. To this end, samples in the crushed and uncrushed forms were fabricated with thicknesses of 30 and 50 mm. The FE-SEM (Field Emission Scanning Electron Microscopy) and Atomic Force Microscopy (AFM) images showed that the studied stones have different morphological and topological surfaces, which in turn lead to different sound absorption coefficients (SACs) and effective thermal conductivities (Keff). It was found that smaller fruit stones with higher surface roughness generally have higher noise reduction coefficients, and this was more pronounced for samples of 50 mm thickness. In addition, samples in the crushed form enjoyed superior sound absorption performance compared with their uncrushed counterparts. The SAC peak in the crushed form appeared at lower frequencies and its value was higher than that of the uncrushed stones. Moreover, when the air gap was introduced, all samples showed excellent sound absorption at frequencies of 400–600 Hz. It was found that, while an increase in sample thickness led to an enhancement in SAC at low and middle frequencies, the Keff values did not significantly change. Uncrushed samples demonstrated enhanced thermal insulation properties compared to their crushed counterparts. The Keff values of the specimens were found to be in the range of 0.087–0.204 W.m−1 K−1, indicating the good thermal insulation performance of the panels. The frequency-dependent SACs of fruit stone panels were predicted using the Johnson-Champox-Allard and Attenborough models, and acceptable consistency was observed.

CNTs/PVA Composite Aerogel for Efficient Microwave and Acoustic Absorption

The lightweight three-dimensional (3D) carbon nanotubes (CNTs) aerogel has garnered significant interest due to their exceptional characteristics, including high porosity, large specific surface area, and a 3D conductive network. These characteristics make it as a promising candidate for various applications in microwave absorption. However, to construct a multifunctional framework, that can swiftly adapt to complex real-world environments, remains a large challenge. In this study, we fabricated a multifunctional CNTs/polyvinyl alcohol composite aerogel (CPA). Integrating polyvinyl alcohol (PVA) into CNTs aerogel could effectively prevent CNTs aggregation, thus obtaining the remarkable electromagnetic absorption, acoustic, mechanical, and thermal properties. The minimum reflection loss (RL) of CPA achieved an outstanding value of -39.77 dB, measured with a thickness of 2 mm. In addition, CPA showed excellent sound absorption performance, with the highest sound absorption coefficient (SAC) of 0.981. Sound transmission loss (STL) could be improved by adjusting the ratio of CPA, the improvement of STL was 5-8 dB at the mid-high frequencies. Finally, CPA also exhibited excellent thermal insulation performance with the lowest thermal conductivity of 0.0297 W/m·k. The multifunctional capabilities of CPA position it as a highly promising material for various applications, such as microwave absorption, noise reduction, and heat preservation.

A multi-layered corrugated resonator acoustic metamaterial with excellent low-frequency broadband sound absorption performance

How to design acoustic metamaterials with excellent low frequency broadband sound absorption and mechanical properties is a concern and bottleneck in the field of structural vibration and noise control. Based on the principle of Helmholtz resonator and lightweight multi-functional sandwich structure, we propose a multi-layered corrugated resonator acoustic metamaterial (MLCRAM) and fabricate a sample using 3D printing technology. Through theoretical and simulated studies of the MLCRAM model, it is presumed that the MLCRAM has excellent sound absorption performance in the frequency range of 500 to 1000 Hz, which is mainly attributed to the parallel combination of resonant cavities. Then the experimental test of the sample is also carried out to verify the reliability of both theoretical and simulated methods. By analyzing the complex frequency plane, the influence of coupling effects between resonant cavities on the sound absorption properties of the MLCRAM. Subsequently, the overall sound absorption mechanism of the MLCRAM is further analyzed in terms of sound velocity, sound pressure amplitude, and power dissipation density. It has been demonstrated that MLCRAM exhibits excellent low-frequency broadband sound absorption performance, providing a reference for the design of novel acoustic metamaterials.

Study on acoustic properties of ultra-low-density polyurethane with Nano-Cellulose

Recently, polyurethane materials are commonly used as engine room sound-absorbing materials to reduce the weight of automobiles. Polyurethane materials have excellent sound absorption performance in the 800~2,000 Hz frequency range due to the structural characteristics of the material, but the sound absorption performance of more than 2,000 Hz is insufficient. In the case of electric vehicles, it is important to improve the high frequency noise generated by the motor, and the need for modification of polyurethane materials has increased. High frequency performance can be improved by improving the air permeability of polyurethane cells through the bonding structure of polyurethane materials, optimization of blowing and gelling reactivity, and the amount of foaming gas. Increased air permeability of polyurethane materials reduces density and strength. In this study, Nano-cellulose is a highly functional new material with light and high mechanical properties through a chain bundle structure. The dispersibility is improved by optimizing the content and particle size of nano-cellulose. The goal is to develop ultra-low-density polyurethane with excellent sound absorption performance in high frequency areas over 2,000 Hz and improved strength. The strength of hood insulation and dash outer products can be improved by applying the developed polyurethane material. In addition, the quality of lightweight engine room sound absorbing materials for electric vehicles can be improved.

Sound Absorption Properties of An Open-Cell Ceramic with A High Occupancy Ratio for Recycling of Sediment from Taihu Lake

This paper proposes an open-cell ceramic acoustic material to combat noise pollution, which utilizes sediment from Taihu Lake as its main ingredient. The open-cell ceramic is manufactured using the gel injection molding method to achieve a high occupancy ratio. Simulation and experimental research demonstrate that the open-cell ceramics possess excellent sound absorption properties, particularly in the middle and high frequencies, with high sound absorption characteristics. The unique pore structure of the open-cell ceramics provides multifunctional and excellent mechanical properties, resulting in a lightweight, pore-designable, and broad-frequency sound absorption material that is environmentally friendly, energy-efficient, and renewable.

Polyacrylonitrile nanofiber reinforced polyimide composite aerogels with fiber-pore interpenetrating structures for sound absorption, air filtration and thermal insulation

Prolonged noise pollution and its induced vibration would not only lead to the failure of instruments and equipment, but also endanger human health. In this work, with water-soluble polyamide acid (PAA) as the matrix and polyacrylonitrile nanofiber (PANNF) as the reinforcement, PANNF reinforced polyimide (PANNF/PI) composite aerogels with fiber-pore interpenetrating structures are fabricated by the method of “homogeneous mixing, freeze-drying and heat treatment”. PANNF that intersperses among pores can effectively inhibit the shrinkage of PI aerogels and enhance sound absorption and mechanical properties. With PANNF dosage of 10 wt%, the composite aerogels own the excellent sound absorption performance, with noise reduction coefficient (NRC) of 0.398, and average sound absorption coefficient (SAC) of 0.913 in the frequency range of 2000∼6300 Hz. The composite aerogels also have excellent mechanical properties, with Young's modulus of 12.42 kPa, stress loss of 3.64% and energy loss coefficient of 0.203. 10 wt% PANNF/PI composite aerogels also possess satisfying air filtration performance (97.2% filtration efficiency for PM2.5, quality factor (QF) value of 0.0396 Pa-1; and 99.4% filtration efficiency for PM10, QF value of 0.0567 Pa-1) and thermal insulation performance (thermal conductivity coefficient as low as 0.036 W/(m·K)).

Optimal design of fibrous materials for sound absorption

Fibrous materials, which are typical porous materials, play a crucial role in noise control and improving sound quality in the building and automotive industries. Researchers have extensively investigated the acoustic properties of fibrous materials, including both natural and synthetic fibers. Additionally, various numerical and semi-phenomenological models have been employed to accurately predict their acoustic properties. Despite the existence of accurate models, most research on the acoustic properties of fibrous materials has been experiment-oriented. Furthermore, very few studies have focused on reliable and straightforward approaches to optimize these properties and guide the preparation process of fibrous materials. This work aims to develop a robust optimization approach for single-layer and multi-layer fibrous materials by combining numerical optimization methods with numerical and semi-phenomenological acoustic models. The ultimate goal of this optimization approach is to provide designed parameters for fabricating fibrous materials with excellent sound absorption properties. To validate and refine the optimization approach, the fabricated fibrous materials will be thoroughly measured.

Topology optimization of porous structures by considering acoustic and mechanical characteristics

Porous structures are widely found in nature and have been extensively studied due to their high stiffness-to-weight ratio, excellent sound absorption, and robustness regarding loading variation. This paper proposes a new topology optimization approach for the design of porous acoustic-mechanical structures based on the three-field floating projection topology optimization (FPTO) method. In order to capture the change of ambiguous structural boundary during topology optimization, the mixed displacement/pressure (u/p) finite element formulation with the linear material interpolation scheme is adopted. The artificial porous features of the structures are generated by imposing the local volume constraint defined by a constant or adaptive filter radius. The 0/1 constraints of the design variables are simulated by the floating projection constraint so that the final design has a clear topology. To verify the effectiveness of the proposed method, some interesting 2D and 3D numerical examples considering their mechanical and acoustic characteristics simultaneously are presented to achieve porous structures by minimizing dynamic compliance, possibly with an additional acoustic constraint. The results also show that the resulting porous features are useful in improving the acoustic performance of the optimized designs.

Sound absorption of space-coiled metamaterials with soft walls

Integrating soft components into acoustic metamaterials is an extremely promising way to enhance their adjustability and reconfigurability. Herein, we report a type of space-coiled metamaterials using soft walls to construct internal channels, denoted as soft-wall space-coiled metamaterials (SSM), exhibiting superior sound absorption performance at low frequencies. The physical mechanism of the SSM is revealed through finite element simulations and sound impedance tube-based experiments. It is demonstrated that the exceptional sound absorption of the SSM originates from the strong coupling effect between the friction-like dissipation along the internal channel and the deformation-like dissipation in the soft wall. The experimental results show that the fabricated SSM sample with a subwavelength thickness (<1/25 wavelength) features near-perfect sound absorption (reaching 0.97 at 615 Hz) and a broad half-power bandwidth (1.6 times that of the rigid-wall space-coiled metamaterials sample with the same geometric dimensions). Moreover, the SSM has excellent sound absorption performance under oblique incidence even when the incident elevation angle reaches 75°. This work may bring inspiration for developing soft-components-integrated acoustic metamaterials with compact, adjustable, and reconfigurable characteristics.

Sound absorption performance of folded structures prepared from woven prepreg and porous material composites

In this study, a composite material composed of a woven prepreg and ventilated felt is designed and prepared in the form of a folded structure to obtain excellent sound absorption performance. Absorption experiments of the woven prepreg, composite material, and folded structure are carried out respectively. The test results show that the composite material has a higher minimum value of the sound absorption curve compared with woven prepreg, which is further improved by the folded structure. The sound absorption coefficient of the structure can be greater than 0.4 in the 400–6300 Hz range. Meanwhile, a theoretical model is established according to the characteristics of the folded structure, which shows good agreement with the experimental results. Finally, the theoretical model is used to analyze the three key factors (thickness of the composite, height of the whole structure, and folding angle) in the design of the folded structure. The results show that increasing the first two factors can significantly change the sound absorption performance of the structure, while the folding angle will not significantly change the sound absorption characteristics of the structure.

A composite acoustic black hole for ultra-low-frequency and ultra-broad-band sound wave control

Achieving ultra-low and ultra-broad-band sound absorption and full-band sound insulation is a major challenge. Here, we propose a composite structure of a multilayer micro-perforated plate and acoustic black holes to achieve this purpose. Combining the stable sound absorption effect of the multilayer micro-perforated plate in the full frequency band and the sound insulation effect of the acoustic black hole in the low frequency and the excellent sound absorption effect in the high frequency, the excellent sound control effect of 600–3150 Hz absorption coefficient greater than 0.8 and 100–3150 Hz sound transmission loss greater than 50 dB is achieved. The acoustic properties of different components and different acoustic black hole outlet were evaluated by finite element method, and the principles of sound absorption and insulation of the composite structure were elaborated. Finally, the results of finite element method are verified by impedance tube experiments. This work can make further progress in elucidating the acoustic properties of the ABH and open up new avenues in the control of ultra-low and ultra-wide frequency acoustic waves.

Porous ceramics based on high-thermal-stability Al2O3–ZrO2 nanofibers for thermal insulation and sound absorption applications

Al2O3 fibers are promising candidates for porous ceramics, but the sudden growth of grains in the fibers above 1200 °C will limit their applications for high temperature. Herein, we reported the successful fabrication of the Al2O3–ZrO2 nanofibers by electrospinning and the nanofiber-based porous ceramics by a combination of gel-casting, freeze-drying and high-temperature sintering. Results show that the addition of Zr could greatly improve the thermal stability (up to 1400 °C) of the Al2O3-based nanofibers, owing to the inhibition of the sudden growth of the grains in the fibers at high temperature. The Al2O3–ZrO2 nanofiber-based porous ceramics after sintering at 1100–1400 °C possessed a multi-level pore structure and exhibited high thermal stability, ultra-high porosity (97.79–98.04%), ultra-low density (0.075–0.091 g/cm3) and thermal conductivity (0.0474–0.0554 W/mK), and excellent sound absorption performance with the average sound absorption coefficient of 0.598–0.770. These porous ceramics are expected to be employed in the fields of high-temperature thermal insulation and sound absorption.

Study on Sound Absorption Performance of Aluminum Foam Combination

Aluminum foam is a kind of new material with a large number of holes distributed in aluminum alloy. It has the characteristics of lightweight, sound absorption, energy absorption and vibration reduction, and other porous materials. Aluminum foam has good acoustic performance. However, its excellent sound absorption ability is only reflected in the middle and high-frequency bands. Besides, the low-frequency sound absorption ability is very poor and the frequency band is narrow. Therefore, in this paper, different types of perforated aluminum foams with different parameters are combined to explore the influence on acoustic performance and find that the combination of large porosity perforated sample and aluminum foam has a better sound absorption effect. The unperforated sample is placed in front of the perforated sample to improve the sound absorption coefficient of the low and medium frequencies. Finally, different types of perforated aluminum foam samples were properly combined, and it was found through the test that almost all sound waves in the band of 1200 HZ~2000 Hz could be absorbed by the combined structure.

Multifunctional flexible SiO2/BNNBs nanofibrous aerogel for thermal insulation, infrared stealth and sound-absorption

Ceramic nanofibrous aerogels have attracted great interest because of their extraordinary multifunctional properties. Herein, a facile strategy was proposed to create SiO2 nanofibers-BN nanoribbons assembled binary aerogel with excellent temperature-invariant super-flexibility, as well as low thermal conductivity, low infrared radiation and excellent sound absorption properties. In addition, the unique structure of the nanofibers-nanoribbon aerogel acts as the thermal insulation layer, combined with Al foil acting as an infrared reflection layer, forming a component that can effectively hide high infrared targets. The nanofibrous-nanoribbons binary aerogel possess low thermal conductivity (0.0288 W/(m⋅K)) and outstanding sound-absorption ability (NRC value of 0.43), as well as excellent infrared stealth ability, which makes it an ideal candidate for thermal insulation and sound absorption in multi fields.

Study of Physicochemical, Flammability and Acoustic Properties of Hookeri raphia Natural from Cameroon

Introduction: The development of new materials is ultimately associated with requirements such as strength, lightness, low production cost, and raw materials from renewable sources, seeking to meet the needs, research, and development of new technologies, which value the qualification of materials from vegetable sources as natural fibers. Method: In this context, this study aimed to characterize the main physicochemical properties of the natural raffia fiber and its flammability and thermo-acoustic characteristics. These characterizations were performed using several techniques, such as chemical composition analysis, density, moisture adsorption, SEM-EDS, FTIR, and TGA/DTG. Result: The results showed that the morphology of the raffia fiber presents a similar shape to the beehive. The Elemental analysis of the natural fiber of raffia shows that carbon and oxygen contents are predominant, representing a proportion of more than 90%. Furthermore, the results suggest that the fiber is composed of lignin, hemicellulose, cellulose, tannin, and extractives, with cellulose in a proportion of 80%. Conclusion: TGA presents a profile similar to large parts of untreated vegetable fibers. The acoustic test showed excellent sound absorption coefficient (α) values at high frequencies, while the flammability test showed that natural raffia fiber is a good flame retardant.

Conductive Three-Dimensional Lamella Network for Improved Sound Absorption and Heat Transfer

Recently, the quality of life of human has been increasingly threatened by noise caused by various surroundings. To prevent damage from noise, research is being conducted on materials that are capable of both blocking noise in a wide frequency range and transferring frictional heat generated from the noise blocking. In this study, using porous melamine foam (MF) as the basic material, a three-dimensional (3D) lamellar structure with excellent sound absorption and thermal conductivity was manufactured using the dipping process and vapor deposition polymerization, respectively. The 3D lamella structure shows excellent sound absorption performance in a wide frequency range of 250–6300 Hz, and in particular, has a sound absorption coefficient value of 0.96 at 4000 Hz. Due to the coating of the structure using polypyrrole as a conductive polymer, it has a higher thermal conductivity value (0.286 W m–1 K–1) than MF (0.033 W m–1 K–1). This structure also has high structural stability and elastic recovery performance, so it has the same mechanical performance, even after 500 repeated deformations.

New Class of Multifunctional Bioinspired Microlattice with Excellent Sound Absorption, Damage Tolerance, and High Specific Strength.

Although mutually independent, simultaneous sound absorption and superior mechanical properties are often sought after in a material. One main challenge in achieving such a material will be on how to design it. Herein, we propose a bamboo-inspired design strategy to overcome the aforementioned challenges. Building on top of the basic octet-truss design, we introduce a hollow-tube architecture to achieve lightweight property and mechanical robustness and a septum-chamber architecture to introduce acoustic resonant cells. The concept is experimentally verified through samples fabricated using selective laser melting with the Inconel 718 alloy. High sound absorption coefficients (>0.99) with broadband spectra, damage-tolerant behavior, high specific strength (up to 81.2 MPa·cm3/g), and high specific energy absorption of 40.1 J/g have been realized in this design. The sound absorption capability is attributed to Helmholtz resonance through the pore-and-cavity morphology of the structure. Microscopically speaking, dissipation primarily occurs via the viscous frictional flow and thermal boundary layers on the air and microlattice interactions at the narrow pores. The high strength is in turn attributed to the near-membrane state of stress in the plate structures and the excellent strength of the base material. Overall, this work presents a new design concept for developing multifunctional metamaterials.

Multi-functional mullite fiber-based porous ceramics with a multilevel pore structure assembled by alumina platelets and mullite whiskers

Mullite fiber-based porous ceramics have been widely used in the field of heat insulation. To further broaden their applications in other fields, such as filtration and sound absorption, mullite whiskers and alumina platelets were introduced as the secondary structural materials in mullite fiber-based porous ceramics by a sol-gel combining heat-treating method, and new fiber-based porous ceramics with a unique multilevel pore structure were developed. By adjusting the molar ratios of aluminium tri-sec-butoxide to aluminium fluoride and calcination temperature, these fiber-based porous ceramics not only presented the characteristics of lightweight (maximum density of 0.38 g/cm3) and good heat insulation (minimum thermal conductivity of 0.11 W/mK) comparable to traditional fiber-based porous ceramics, but also showed a superior specific surface area (up to 11.5 g/m2) and excellent sound absorption performance (average sound absorption coefficient as high as 0.728). Owing to these outstanding characteristics, the corresponding porous ceramics are expected to be promising multifunctional materials in diverse fields, especially thermal insulation and sound absorption.

Reduced Space Optimization‐Based Evidence Theory Method for Response Analysis of Space‐Coiled Acoustic Metamaterials with Epistemic Uncertainty

Acoustic metamaterials have been widely concerned by researchers because of their excellent sound absorption properties. Traditional uncertainty analysis methods for response analysis of acoustic metamaterials with evidence variables have limitations. The excessive time spent on repetitive extreme analysis of focal elements severely impedes the practical application of evidence theory. To reduce the computational costs of uncertainty quantification for acoustic metamaterials under the evidence theory, a reduced space optimization‐based evidence theory method (RSO‐ETM) is proposed. In RSO‐ETM, a simplified surrogate model is first constructed by a modified adaptive arbitrary orthogonal polynomial (MAAOP) expansion method, and then, the monotonicity of the response surface is examined to reduce the space. Subsequently, the Newton iteration technique and a transformation boundary method are used to obtain the extreme points in the reduced space, through which the boundary of the response over each focal element can be readily obtained. By using RSO‐ETM, the optimization for each focal element can be avoided, and correspondingly the computational costs are reduced. Two mathematical examples and acoustic problems are employed to demonstrate the practicality of the methods.

Design and optimization of micro-perforated ultralight sandwich structure with N-type hybrid core for broadband sound absorption

We propose a novel ultralight multifunctional micro-perforated sandwich structure with N-type hybrid core, which exhibits excellent sound absorption as well as good load-bearing capacity and heat transfer performance. Sound absorption coefficient of the sandwich structure is calculated by establishing an analytical model. To validate the analytical model predictions, both experimental measurements and numerical simulations are carried out, with good agreement achieved. Physical mechanisms leading to the excellent acoustic performance of the structure are revealed, and effects of geometric parameters are quantified. For maximized sound absorption at minimal structural weight, an optimization strategy is developed with the Simulated Annealing algorithm. Compared with non-optimal sandwich structures, the optimal structure enables reduced weight and better absorption within broader frequency range. The proposed ultralight sandwich structure with integrated multifunctional attributes has significance in engineering applications demanding excellent mechanical, thermal, acoustic performances as well as low mass and volume.