Sound Absorption Mechanism Research Articles

Mechanism of airborne sound absorption through triboelectric effect for noise mitigation

Mitigating broadband noise with passive airborne sound absorbers has been a long-lasting challenge, particularly for low-frequency anthropogenic sounds below kilohertz with long wavelengths, which require bulky materials for effective absorption. Here, we propose a strategy that utilizes local triboelectric effect and in-situ electrical energy dissipation mechanism for airborne sound absorption. This approach involves a fundamentally different mechanism that converts airborne sound into electricity for energy dissipation, in contrast to conventional mechano-thermal energy conversion mechanisms. We establish an equivalent acoustic impedance model to provide theoretical analysis of the underlying sound absorption mechanisms, with a theoretical maximum mechano-electro-thermal coupling efficiency approaching 100% under optimal conditions. We design fibrous triboelectric composite foam materials accordingly and show their substantially boosted acoustic absorption performance experimentally, where the adoption of diverse triboelectric material pairs validates that a larger difference in material charge affinities intensifies the local triboelectric effect and results in higher acoustic absorbing performance.

Inverse-designed acoustic metasurfaces for broadband sound absorption

Acoustic metasurfaces are widely used for noise attenuation due to their outstanding acoustic performance and subwavelength characteristics. The paper introduces a topology-optimized inverse design approach for broadband sound-absorbing metasurfaces, aiming to achieve efficient sound absorption performance across a wide frequency spectrum. By integrating genetic algorithms with the finite element method and driven by objectives such as the absorption frequency range and absorption coefficient, we can transcend the limitations of manual design and fully exploit the design potential of structures. Furthermore, the study investigates the sound absorption mechanism and thermal-viscous dissipation through finite element simulations and experimental validations. The research findings reveal that the proposed broadband sound-absorbing metasurfaces demonstrate excellent sound absorption capabilities across the designated frequency range, boasting an average sound absorption coefficient exceeding 85%. These findings offer fresh perspectives and methodologies for advancing the research and practical application of broadband sound-absorbing metasurfaces.

Efficient and broadband sound absorption properties of slotted aluminum foam

To enhance the sound absorption performance of aluminum foam, a slotted structure was developed. Firstly, the theoretical model of sound absorption for the slotted aluminum foam was established by the transfer matrix method. Secondly, the finite element model was established using COMSOL software to predict the sound absorption coefficient. The reliability of the theoretical and finite element models was validated through impedance tube experiments. The sound absorption mechanism is investigated by analyzing the internal sound field. Finally, the sound absorption properties of aluminum foam with other slot patterns are investigated. Additionally, the factors that influence sound absorption properties are investigated. The results indicate that the slots alter the sound pressure distribution within the material, inducing a pressure diffusion effect. When sound waves enter the interior of the material through the narrow slots, they are absorbed and dissipated by the matrix material on the sides of the slots. The sound absorption coefficient can be improved by increasing the thickness, slot scale, and slot depth of the slotted aluminum foam. Specifically, when the slot depth is 15 mm, and the slot width is 5 mm, the average sound absorption coefficient of incompletely slotted aluminum foam in the frequency range of 1000 ∼ 6300 Hz is 0.86, which can realize broadband sound absorption. With the increase of slot depth, the sound absorption peak becomes more pronounced.

A fundamental investigation on the sound absorption characteristics of acoustic meta-surface type baseboards

The sound of footsteps generated in corridors propagates into surrounding spaces, sometimes becoming a problem of noise pollution. Therefore, the aim of this study is to reduce footstep noise by incorporating sound absorption mechanisms into the baseboard of corridors. We focus on the acoustic metasurface that has gained significant attention in recent years in order to absorb a relatively wide range of frequencies. In this study, we proposed acoustic metasurface type baseboards by utilizing multiple resonators with different resonance frequencies. The proposed models feature parallel arrangement of multiple resonators with straight or inclined slits. The absorption performance of these models is evaluated through theoretical analysis, numerical simulations, and experiments. Results suggest that acoustic metasurface type baseboards is found to be able to absorb the dominant frequencies in the sound of footsteps. In addition, increasing the number of resonators and incorporating slanted perforations in the neck contribute to improved absorption performance. Furthermore, the possibility of thinning the models through slanted perforations is also suggested.

Centrifugal pump impeller wheel inspired acoustic metamaterial for low frequency sound absorption

Addressing low-frequency noise is a significant concern within the realm of acoustics and noise management. Labyrinthine channel based acoustic metamaterials have been proved to control low frequency noise using local resonance effect and thermoviscous dissipations. Drawing inspiration from centrifugal pump impeller wheel, an acoustic metamaterial absorber has been devised. The design incorporates impeller vanes to create a channel with variable widths and a micro-perforate panel through which sound wave propagates to the channels. Numerical simulations using COMSOL Multiphysics and experimental analysis are conducted employing Two microphone impedance tube method. Acoustic pressure and acoustic particle velocity distribution plots from numerical simulation study are used to comprehend the sound absorption mechanism. Sound absorption coefficient results reveal that this design offers a tunable sound absorption peak in low frequency regime. Furthermore, this paper discusses the influence of various geometric parameters such as, number of vanes, panel thickness and micro-hole diameter. The subwavelength dimensions of the design contribute to noise control in machineries with space constraints.

Revisiting the sound absorption mechanisms of a finite flexible perforated panel absorber using a numerical approach.

This study investigates the sound absorption mechanisms of a finite flexible perforated panel absorber. Different from existing work where the mechanisms were often investigated by comparing the sound absorption coefficient curves of different absorber configurations, a numerical approach, called virtual impedance tube (VIT) technique, is developed and used for the analysis. One advantage of this technique is the vast dataset generated can be used to investigate the sound absorption mechanisms from an energy standpoint. The developed VIT technique is first validated using the impedance tube test, where a proportion-integration-differentiation control algorithm is developed to maintain the incident sound at a desired sound pressure level. Then, the sound absorption mechanisms at three absorption peaks, i.e., hole-cavity controlled, panel-cavity controlled, and panel controlled, are investigated and the dominant energy dissipation mechanism at different sound pressure levels (SPLs) is revealed. Finally, an impedance model that takes account of the panel vibration and is applicable to various SPLs is proposed and validated.

Sound absorption properties and mechanism of multi‐layer micro‐perforated nanofiber membrane

AbstractAiming at achieving low‐frequency and broadband sound absorption under the premise of light and thin layers, in this paper, polyvinyl butyral (PVB) nanofiber membranes were micro‐perforated and then combined sequentially to prepare multi‐layer micro‐perforated nanofiber membrane (MPNM) for acoustic noise reduction. It was demonstrated that the multi‐layer MPNM exhibited a high absorption (constantly over 50%) in the frequency of 480–2500 Hz. In addition, the established theoretical model of the sound absorbing coefficient can accurately predict the sound absorption performance of the structure with different layers, which can provide a theoretical foundation for the design of the structure of the nanofibrous membrane acoustic absorber. Based on the proposed acoustic model, the relationships between the absorption properties and the parameters were investigated, and it was found that the effective acoustic absorption frequency range and acoustic absorption coefficient curve of the multi‐layer MPNM were closely related to the size and arrangement of hole diameter, perforation rate, fiber membrane thickness, and cavity depth. Optimization of the structural parameters utilizing algorithms can achieve superior sound absorption performance, with an average absorption coefficient of 0.81 in the frequency of 100–2500 Hz. This study provides a theoretical and experimental basis for the development of low‐frequency sound‐absorbing materials and is of great significance for optimizing the acoustic performance of nanofiber membranes and expanding their applications in various acoustic engineering applications.

Development of a low-frequency broadband sound absorber based on a micro-perforated panel coupled with the Helmholtz resonator system

In the field of vibration and noise reduction, micro-perforated panel (MPP) structures and Helmholtz resonators (HR) play crucial roles as common sound-absorbing elements. However, independently applied MPP and HR structures cannot provide sufficiently wide absorption bandwidths at low frequencies. To achieve low-frequency broadband sound absorption, this study proposes a novel low-frequency broadband sound absorption structure (EMH) based on MPP and HR with a thickness of 40 mm to achieve a subwavelength, efficient, and compact design. We establish theoretical models of MPP and HR coupled systems, systematically analyze the sound absorption performance of same-element and different-element coupled structures, and employ the particle swarm optimization (PSO) algorithm to obtain structural parameters for efficient coupled sound absorption. Furthermore, we compare the sound absorption performance of three optimized coupled structures (MPP-coupled (SM), HR-coupled (SH), and MPP and HR-coupled) from the perspective of the theoretical calculation of the sound absorption coefficient and finite element analysis of the sound absorption mechanism. Finally, samples fabricated using 3D printing technology are tested in an impedance tube. The results demonstrate that efficient coupled sound absorption of MPP and HR can be achieved through parameter optimization. SH and SM exhibit nearly perfect sound absorption in the frequency ranges of 323–495 Hz and 615–1600 Hz, respectively, whereas the effective absorption bandwidth of EMH can reach 1225 Hz in the range of 200–1600 Hz. EMH shows superior low-frequency broadband sound absorption performance with a lightweight and simple structure, which holds the potential for application in low-frequency noise control.

Experimental and numerical evaluation of the influence of voids on sound absorption behaviors of 3D printed continuous flax fiber reinforced PLA composites

This study aims to quantitatively analyze the effects of voids on sound absorption properties of 3D printed continuous flax fiber reinforced PLA composites (CFFRCs). Three kinds of flax yarns with different linear density were employed to prepare CFFRCs via 3D printing technology. The sound absorption performances of these composites were measured using the impedance tube based on the two-microphone transfer function method. The microstructure morphologies including cross-sections of flax yarns, voids shape and distributions of the composites were observed via ultra-depth microscope and micro-computed tomography to reconstruct the exact structures in simulation. Mercury intrusion porosimetry was applied to measure the voids dimensions of CFFRCs. The influence of voids on sound absorption mechanisms of CFFRCs were revealed based on thermoviscous acoustics theory by conducting the simulation in COMSOL software. The experimental results demonstrated that CFFRCs exhibited excellent sound absorption coefficients (close to 1) within the frequency range of 150–350 Hz and 350–550 Hz, resulting from the voids inside and between the flax yarns respectively. With the increase of linear density (diameter of the yarn), the contents of voids inside and between the flax yarns both increased. The dimensions of voids inside the flax yarns improved while those between flax yarns remained unchanged. The existence of the voids between the flax yarns resulted in a decrease in the sound absorption coefficient of CFFRCs, while more voids inside flax yarns led to the increase of the sound absorption frequency. Numerical results indicated that voids between the flax yarns contributed to a more uniform change in sound speed, reducing sound absorption performance. Whereas, voids inside the flax yarns could improve viscous friction of soundwaves due to narrow structures, enhancing sound absorption capabilities. This study is anticipated to provide a guidance for the design of integration of structure and function of 3D printed CFFRCs.

Advancing Sustainable Acoustic Solution: Exploring the Sound Absorption Characteristics of Biodegradable Agricultural Wastes, Coconut Fiber, Groundnut Shell, and Sugarcane Fiber

Among the world's greatest threats is noise pollution particularly in megacities that affect the quality of life. This problem can cause negative effects on human health, disturbing emotion as well as human behavior. Natural fiber sound insulation materials have been demonstrated to be a potential substitute for the synthetic products currently employed in the sound insulation industry. Coconut fiber and sugarcane fiber happen to be biodegradable, earth-friendly, and present lower risks to the environment and human health. The research examines the sound absorption characteristics of natural biodegradable waste fibers (coconut fiber & sugarcane fiber) to evaluate their suitability as sound absorbers. The paper seeks to discover the internal workings of the sound absorption mechanisms of these materials and also to help design environmentally friendly acoustic solutions.

Review of Underwater Anechoic Coating Technology Under Hydrostatic Pressure

AbstractThe underwater anechoic coating technology, which considers pressure resistance and low-frequency broadband sound absorption, has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence. One the one hand, controlling low-frequency sound waves in water is more challenging than in air. On the other hand, in addition to initiating structural deformation, hydrostatic pressure also changes material parameters, both of which have a major effect on the sound absorption performance of the anechoic coating. Therefore, resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult. Particularly, a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure. Based on the influence of hydrostatic pressure on underwater anechoic coatings, the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms, analysis methods, and structural designs is reviewed in this paper. Finally, the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized, providing a reference for the design and research of low-frequency broadband anechoic coating.

Sound absorber based on a sonic black hole and multi-layer micro-perforated panels

In order to achieve low-frequency and broadband sound absorption simultaneously, we propose a structure that combines a sonic black hole with multilayer micro-perforated panels. Firstly, we present finite element models for composite structures based on sonic black holes and micro-perforated panels and describe the sound absorption mechanism of the composite structure by comparing the sound absorption phenomena of micro-perforated panels with sonic black holes and micro-perforated panels with ordinary circular tubes. Secondly, the effects of the end coordinates of the sonic black hole, the number of panels and the parameters of the micro-perforated panels are discussed. Thirdly, the theoretical model of the proposed structure is developed using the transfer matrix method. Finally, the sound absorption test of the proposed structure is carried out using impedance tubes. The test results show that the sound absorption coefficient of the sample with a geometric length of 203 mm reaches 0.8 at 223 Hz and stabilizes above 0.9 at 398–1600 Hz. The sound absorber based on a sonic black hole and multi-layer micro-perforated panels has excellent sound absorption performance and has great research potential and application value.

Sound absorption performance and mechanism of aluminum foam with double-layer structures of conventional and porous cell walls

Open-cell aluminum foam exhibits sound absorption valleys in the 2500-4000 Hz range, reducing its sound absorption performance in the 800–6300 Hz range. This paper prepared a novel aluminum foam with a double-layer structure using the infiltration casting method, and its pore structure, sound absorption performance, acoustic model, and sound absorption mechanism are investigated. The double-layer structure consists of a conventional pore (CP) layer with a single pore size of 250 μm or 600 μm and a porous cell wall (PCW) layer with double pore diameters of 250 μm and 600 μm. As the thickness ratio between the CP and PCW layers decreases, the acoustic absorption valley value of the double-layer structure increases when combined with a small-pore CP layer. In contrast, it decreases slightly when combined with a large-pores CP layer. The double-layer structure reaches a sound absorption valley value and average sound absorption coefficient of 0.912 and 0.902, respectively. The double-layer structure's sound absorption valley value is better than that of a homogeneous structure, improving sound absorption performance. A Lu modified model is established to characterize the sound absorption of the double-layer structure, which closely matches the experimental results. The modified model further analyzed the vital geometrical parameters affecting the absorption valleys. Acoustic impedance analysis shows the enhanced sound absorption valleys are due to: 1) Gradient acoustic impedance reduces sound reflections at the air-structure interfaces and increases secondary reflection at the interfaces in the structure; 2) The series–parallel configuration increased the resonance peak bandwidth, while the dual-sized resonance cavities regulated the resonance peak frequency.

Recent Advances in Preparation and Structure of Polyurethane Porous Materials for Sound Absorbing Application.

Various acoustic materials are developed to resolve noise pollution problem in many industries. Especially, materials with porous structure are broadly used to absorb sound energy in civil construction and transportation area. Polyurethane (PU) porous materials possess excellent damping properties, good toughness, and well-developed pore structures, which have a broad application prospect in sound absorption field. This work aims to summarize the recent progress of fabrication and structure for PU porous materials in sound absorption application. The sound absorption mechanisms of porous materials are introduced. Different kinds of structure for typical PU porous materials in sound absorption application are covered and highlighted, which include PU foam, modified PU porous materials, aerogel, templated PU, and special PU porous materials. Finally, the development direction and existing problems of PU material in sound absorption application are briefly prospected. It can be expected that porous PU with high sound absorption coefficient can be obtained by using some facile methods. The design and accurate regulation of porous structures or construction of multilayer sound absorption structure is favorably recommended to fulfill the high demand of industrial and commercial applications in the future work.

Meta-structure based on coupled resonators for low-frequency broadband sound absorption

This work investigates and explains the behavior of an acoustic meta-structure based on different coupled Helmholtz resonators (HR). The analytical formulation of the Maa model is used to represent both the acoustic impedance and the sound absorption mechanism of the absorber. The structures are numerically modeled using finite element method and validated experimentally in an impedance tube considering sound waves of normal incidence. The absorber samples were manufactured in ABS (acrylonitrile butadiene styrene) polymer material with the additive manufacturing technique by extrusion of material. The results of the impedance tube, numerical and theoretical tests showed agreement and the sound absorber showed a sub-wavelength scale with perfect sound absorption ( 0.97) and broadband of 292 Hz in the low frequency region (200 - 600 Hz). We deduced that the excellent experimental result obtained is due to the high resolution used in the sample manufacturing (± 0.1 mm) which minimized manufacture errors. Finally, the influences of the main parameters of the HR panel (width and depth of the micro-slit) on the sound absorption coefficient of the absorber were also analyzed.

Research on noise reduction methods for indoor substations based on resonant sound absorption

Aiming to reduce the impact of substation noise on the lives of surrounding residents, improving the low and middle frequencies acoustic performance of traditional resistive mufflers in indoor substations is significant. The paper is based on the resonance sound absorption mechanism, and for the first time applies multi-frequency resonance noise reduction technology to the research field of indoor substation noise control, proposing a multi-frequency resonant muffling structure. The acoustic performance of the proposed muffler unit is investigated through theoretical and numerical analysis. The measured noise data of the indoor substation is used as sound excitation in the numerical analysis. The results show that at frequencies of 100 Hz, 200 Hz, 300 Hz, 400 Hz, and 500 Hz, the noise in indoor substations is significantly reduced by the multi-frequency resonant muffling structure. The paper provides references for the application of multi-frequency resonant mufflers in the field of noise control of indoor substations.

Acoustic metasurface embedded with thin-walled plate based on phase modulation for multi-angle broadband sound absorption

The design of low-frequency broadband acoustic absorbers with thin thicknesses is a longstanding and challenging problem. This work proposes an acoustic metasurface consisting of macro-perforated porous, thin-walled perforated plate, and meta-porous layers embedded by thin-walled plate (MPM) to combine the advantages of porous material and resonator. MPM is formed by four subunits with a phase gradient. The acoustic properties of an MPM unit cell are investigated by a theoretical model based on homogenization theory and transfer matrix methods, and the theoretical model is verified by a numerical model. Then, the sound absorption mechanism of MPM unit cell is explored, and it is revealed that the mid-frequency and low-frequency sound waves are mainly dissipated by thin-walled perforated plate and meta-porous layers, and the macro-perforated porous structure target high-frequency absorption. In addition, the dependence of geometric parameters of MPM unit cell on acoustic performance and reflected phase is investigated. Furthermore, the geometric parameters of each subunit in acoustic metasurface are carefully designed, and excellent absorption in target frequency is obtained by the hybrid resonance of a single unit cell and the surface wave conversion of MPM with reflected phase gradient. Also, the appearance of perfect sound absorption comes from the far-field interference between reflected waves and the wave-trapping phenomenon near the periodic structure. A thin (λ/20) absorption panel MPMs is designed to achieve multi-angle low-frequency broadband absorption and an effective normal sound absorption (>50 %) band over 344–3000 Hz. This work proposes a novel design idea and opens possibilities for acoustic metasurface practical applications in noise mitigation of various scenarios.

Geometric design and performance analysis of a foldcore sandwich acoustic metastructure for tunable low-frequency sound absorption

Acoustic metamaterial structures have received extensive attention for sound and vibration engineering applications from the scientific community in recent years. However, the real-life application of conventional acoustic metamaterial structures is frequently limited by fixed frequency bands and increased structural thicknesses in low-frequency noise reduction. In this study, we introduce an origami-based acoustic metamaterial structure that consists of a Miura-ori foldcore, along with a perforated and an unperforated panel. The proposed Miura-ori foldcore sandwich acoustic metastructure (MOF-SAM) exhibits adjustable low-frequency sound absorption capacities due to the foldability of the origami foldcore. Moreover, we employ numerical methods to investigate the sound absorption properties of the MOF-SAM, quantified by the sound absorption coefficient. The results indicate that the structure has a single absorption peak which is superior to that of acoustic structures composed of conventional honeycomb cores. The dissipation of acoustic energy is due to the structural vibrations of the metastructure and the losses in the folding process of the origami foldcore. The numerical results of this study show that the proposed sound absorption mechanism enables tunable low-frequency sound absorption. The geometric design and periodicity of the origami unit fragments offer multiple distinct absorption peaks and thus tunable acoustic performance. These findings of this study are expected to inspire novel designs for next-generation acoustic devices.

Tunable acoustic metamaterial for broadband low-frequency sound absorption by continuous acoustic impedance manipulation

In this paper, a continuously tunable acoustic metamaterial is proposed for broadband low-frequency sound absorption. The metamaterial can be considered as a reconfigurable Helmholtz resonator with an upper perforated panel that can be continuously rotated to adjust the neck length. A theoretical model is developed to study the tunable sound absorption performance of the metamaterial, which demonstrates that it exhibits efficient low-frequency sound absorption ([Formula: see text]) in the frequency range (from 186 Hz to 319 Hz). Furthermore, perfect sound absorption ([Formula: see text]) is achieved at 197 Hz with a deep subwavelength thickness ([Formula: see text]). To validate this model, numerical simulations and experimental measurements are performed, and the physical mechanism of tunable sound absorption is explored. Results show that the acoustic impedance manipulation is realized by rotating the perforated panel to tune the acoustic mass of the Helmholtz resonator, which is the key to the continuous tunability of the proposed metamaterial. Based on the continuous tunability of each metamaterial unit, a tunable broadband sound absorber is designed to achieve a variety of broadband sound absorption performance with a single fabricated structure. This work paves the way for the manual realization of flexible tunability of sound absorbers and helps to achieve tunable absorption of complex noise according to variable acoustic application scenarios.

Structural characteristics properties of sugarcane bagasse and its sound absorption as composites

Noise pollution is one of the serious environmental pollutions. In recent years, the preparation of sound absorption composites using natural fibers as reinforcement material has attracted much attention. Sugarcane bagasse is a by-product of sugarcane. In order to improve the utilization rate of sugarcane bagasse, enrich and expand the application field of its renewable resources, sugarcane bagasse as a reinforcement material, and polycaprolactone as a matrix material are used to prepare sugarcane bagasse/polycaprolactone sound absorption composites by hot press molding technology to analyze the sound absorption performance. The sound absorption mechanism of the sugarcane bagasse sound absorption composites is revealed. First, the structural characteristics of sugarcane bagasse were characterized, and the relationship between its structure and sound absorption performance was analyzed. Second, the effects of sugarcane bagasse length, mass fraction, hot pressing pressure, hot pressing time, and hot pressing temperature on the sound absorption performance were investigated by one-factor analysis. The results show that when the length of sugarcane bagasse was 1.0 mm, the mass fraction was 35%, the hot pressing pressure was 12 MPa, the hot pressing time was 20 min, and the hot pressing temperature was 130°C, the average sound absorption coefficient was 0.38, the noise reduction coefficient was 0.31, and the maximal sound absorption coefficient was 0.80. This study provides an experimental and theoretical basis for the research and development of sound absorption composites made of sugarcane bagasse, and provides a new solution for the recycling of sugarcane bagasse.