Sound Absorption Performance Research Articles

Simultaneously enhanced the sound absorption coefficient and dimensional stability of Carboxymethyl cellulose/clay aerogel by impregnating polyurethane

Carboxymethyl cellulose (CMC) aerogel could be used in the manufacture of highly efficient sound-absorbing materials because of its low density and sustainability. However, owing to its low mechanical strength and brittleness, preparing porous sound absorption materials with excellent sound absorption performance has always been a challenging problem. Herein, carboxymethyl cellulose/organic exfoliation of montmorillonite/thermoplastic polyurethane (CMC/OMMT/TPU) composite aerogels were successfully obtained via a simple impregnation and freeze-drying process. The effect of TPU and OMMT on the sound absorption properties of cellulose aerogels was detailedly discussed. The results revealed that the CMC/OMMT/TPU composite aerogel had hierarchically porous structures, and the sound absorption performance was significantly improved. The average sound absorption coefficient of CMC/OMMT/TPU composite aerogel could reach as high as 0.807 (500–6500 Hz). The main reason for this improvement is caused by the multiple scattering of sound waves on the arranged porous surface, as well as the viscous damping of the air inside the structure between the TPU, CMC and OMMT. Furthermore, the dimensional stability of the prepared aerogel is also greatly enhanced after using TPU. This work provides a new approach for the development of aerogel with stable morphology and sound absorption performance, which would be widely used in construction and military fields.

Random incidence sound absorption of micro-perforated panel absorbers backed with parallel-arranged cavities of different depths

This study investigates sound absorption performance of a kind of wideband micro-perforated panel (MPP) absorbers with parallel-arranged backing cavities at different depths in a diffuse field. An analytical prediction model is presented for evaluating the random incidence absorption coefficient of this type of absorbers, and it exhibits excellent agreement with finite element model and experimental measurements. Then, numerical cases were established using this model to investigate the absorption characteristics of this type of absorbers under random incidence, considering the influence of cavity depths and MPP parameters. Results show that the cavity depth and MPP perforation diameter in this absorber are primary influencing parameters controlling the overall sound absorption performance. Cavities at different depths introduce multiple resonant absorption peaks, while the perforation diameter determines matching conditions between the MPP and air impedance, which simultaneously broaden the absorption bandwidth of this MPP absorber. Although individually adjusting the panel thickness and perforation rate has a smaller impact compared to the perforation diameter, the interaction between these two parameters has significant influences across the entire absorption frequency band.

Spectrum-driven acoustic metasurface for broadband noise control

To address the issue of broadband noise with tonal characteristics in indoor environments, a spectrum-driven acoustic metasurface (SAM) is proposed in this study. By combining the concept of coiled-up space with the synergetic effect between cascaded Helmholtz resonators, SAM with compact size can achieve targeted absorption of broadband noise with arbitrary tonal characteristics. Furthermore, an inverse design method based on genetic algorithms is proposed to regulate the sound absorption performance of SAM and its effectiveness is demonstrated through a case study on controlling transformer noise. Experimental results show that with a subwavelength thickness, SAM can efficiently absorb both the low-frequency noise of the transformer and the broadband noise of the cooling fans. The average sound absorption coefficient within the frequency range of 500–1000 Hz is 0.8, and reaches up to 0.85 at 100 Hz. This study provides theoretical guidance for targeted regulation of broadband noise with multiple low-frequency tonal components.

Experimental assessment and numerical simulations of marine fouling effect on underwater sound absorption coatings

Underwater sound absorption coatings capable of absorbing sound energy is essential to conceal underwater vehicles. While the accumulation of marine fouling on surfaces of ship hulls, platforms, and submarines can significantly alter their acoustic properties. Currently, the precise impact that different stages of marine fouling have on underwater sound absorption coatings remains unclear. In this study, a novel lab assessment method was developed to investigate the acoustic effect of marine fouling on the underwater sound absorption coatings. Four distinct stages of marine fouling were artificial fabricated and characterized, including conditioning film, microfouling, medium macrofouling, and heavy macrofouling. These effects are quantified through comprehensive tests conducted in a water-filled impedance tube. It is found that the first two stages of marine fouling have a negligible impact on the underwater sound absorption performance within the low frequency range of 500 Hz and 2000 Hz. While a limited impact is observed in the frequency range of 2000 Hz–5000 Hz, where the sound absorption coefficient remains approximately 0.6. Conversely, in the third and fourth stages of fouling, the average sound absorption coefficient drops from 0.8 to 0.2. Further, a new acoustic finite element method (FEM) model of hard fouling was developed to predict the acoustic effect, and the numerical results show the same trend with the experimental results. These findings emphasize the importance of considering antifouling strategies during the design of underwater sound absorption coatings, with a particular focus on targeting hard fouling organisms as the primary objective.

Enhancement of acoustic properties of carbon fibrous membrane (CFM) by in-situ crystallization of PZT nanogenerators (PENGs) inside the fibers for a low-frequency acoustic energy harvesting

Acoustic energy harvesting (AEH) by a nanostructured membrane has recently gained increasing attention. This study focused on a novel approach for in-situ crystallization of Pb(Zr0.58Ti0.42)O3 (PZT) as a piezoelectric nanogenerator (PENG) inside the carbon fibrous membranes (CFM). The electrospinning process and post-heat treatment were applied to synthesize the CFM-embedded PENG, which benefits from both the flexibility of carbon fibers and the piezoelectric properties of the crystallized PZT. The results indicated that the carbon fibers kept their microstructure over the heat treatment at 250 and 350 °C while the crystallization fraction of PZT increased. The XPS analysis revealed that the CFM embedded by in-situ crystallized PENG had a higher diversity of tetragonal and rhombohedral in comparison with the CFM embedded by the pre-crystallized PENGs. Furthermore, the electrical conductivity, dielectric constant, and ferromagnetic properties of CFM were improved with the incorporation of the in-situ crystallized PENGs. The acoustic studies in the range of 250–2000 Hz under sound pressure of 90 dB revealed that sound absorption performance of CFM was increased by about +35 %. Also, the ability of CFM in the AEH process was enhanced drastically by embedding the PENGs inside the carbon fibers. The maximum harvested electricity at 500 Hz was 5.9 and 13.9 W m−2 by CFM embedded by in-situ crystallized and pre-crystallized PENGs, respectively. The above results exhibit the great potential for the CFM-embedded PENGs to be used in low-frequency AEH applications.

Multifunctional hybrid plate lattice structure with high energy absorption and excellent sound absorption

Lattice structures are featured by their extraordinary mechanical performances in specific stiffness, specific strength, energy absorption, and sound absorption, etc. The recent trend of multifunctionality in engineering applications has raised new requirements for the integration of their mechanical and acoustic properties. In this paper, a multifunctional hybrid plate lattice structure denoted as SBHP is proposed by hybridizing the traditional body-centered cubic plate (BCCP) and simple cubic plate (SCP) lattice structures, and its acoustic and energy absorption properties are investigated by theoretical modeling, simulation analysis and experimental verification. The effects of hole diameters and plate thicknesses on the sound absorption performance are investigated by impedance matching and system damping state analysis. The results show that the average sound absorption coefficient of SBHP-1 is increased by 24% and 62%, and the normalized half-absorption bandwidth is enlarged by 45% and 89% than those of BCCP and SCP, respectively. Heterogeneous lattice structures constructed by using the synergistic mechanism of strong and weak coupling have a more outstanding broadband sound absorption effect. This work provides an effective approach for the design of multifunctional lightweight structures with excellent broadband sound absorption and high energy absorption.

Ultralight and strain-sensitive bacterial cellulose derived carbon fiber-reinforced graphene aerogel for broadband sound absorption

The growing severity of urban noise pollution poses a threat to the physical and mental health of residents, prompting the need for the development of effective sound-absorbing materials. Herein, we present a versatile method to fabricate ultralight and flexible graphene-based aerogels by introducing one-dimensional carbon fibers as reinforcements. These carbon nanofiber-reinforced graphene aerogels (CNF/GAs) were obtained by the carbonization of freeze-casted bacterial cellulose/graphene oxide (BC/GO). Our CNF/GAs possess a low apparent density (∼3.05 mg cm−3) and exhibit broad-band sound absorption performance with a superior noise reduction coefficient (NRC) as high as 0.65 at a thickness of 30 mm. Meanwhile, their excellent elasticity endows the CNF/GAs with strain-sensing capability, enhancing their capacity for detecting deformations when utilized as sound absorbers in engineering applications. Additionally, the highly porous structure makes the CNF/GAs excellent thermal insulators, with a thermal conductivity as low as 0.011 W m−1 K−1, further expanding their environmental reliability. Therefore, our approach develops CNF/GAs with excellent broad-band sound absorption performance and mechanical-environmental reliability, showing significant practical potential.

The Effectiveness of Styrofoam Mixtures in Lightweight Concrete Walls

This research explores the potential use of styrofoam concrete as a sustainable construction material with excellent acoustic properties. Considering variations in the thickness of styrofoam concrete, the study employs the NoiSee application on smartphones as an affordable and flexible noise measurement tool. The results investigate the potential of using styrofoam to reduce noise. The findings indicate that styrofoam, especially at a thickness of 4 cm, exhibits high effectiveness with a noise reduction of up to 60%. Additionally, the addition of styrofoam waste to brick mixtures can enhance the sound absorption coefficient at 800 Hz frequency. Styrofoam is effective in sound absorption below 1000 Hz, with thickness ranging from 1 cm to 3.5 cm improving sound absorption performance at various frequencies, while a thickness of 4 cm proves effective at 1000 Hz frequency. Overall, the combined results affirm the potential of styrofoam as a customizable soundproofing material for various acoustic applications.

Study on Sound Absorption Properties of Polyvinyl Chloride (PVC) Film Multicavity Structure Materials

Since the development of industry, sound absorption and noise reduction have gradually become an urgent problem to be solved. Lightweight polymer film materials are very effective in response to sound waves, and sound waves can easily cause vibration of the film, which can convert sound energy into vibration and film friction to achieve sound absorption. The application conditions of the film material are very harsh, that is, a support body is required to fix the film and the film needs to be tensioned. The film is very thin and easy to damage. The idea of this research is to transform the film into a bubble structure and use a large number of film bubbles to form a cavity structure material. As a unit of the sound absorption structure, bubbles can avoid damage to the film. In this paper, commercial polyvinyl chloride film bubble materials are used to prepare two kinds of film multicavity structure materials, and the sound absorption performance of this film multicavity structure material is studied. The research results show that this film multicavity structure material has very excellent broadband sound absorption performance, which changes the narrow band sound absorption properties of the usual film single cavity. The average sound absorption coefficient can reach 0.84 in frequency range from 500 Hz to 6400 Hz. This structural material has a single peak sound absorption curve at the middle and low frequency bands, which is the characteristic of resonance sound absorption. And at the middle and high frequency bands, it exhibits the characteristics of broadband sound absorption. The film multicavity structure material has both cavity sound absorption and broadband sound absorption characteristics.

Preparation and Modification of Flexible Polyurethane Foam for Effective Flame Resistance and Sound Absorption

Polyurethane foam as an important sound absorption material is limited by the poor flame resistances in building field, but the modifications of flame resistances tend to have adverse effects on the sound absorption performance. Herein, dibutyltin dilaurate and triethylenediamine are used simultaneously as catalysts, and four new types of flame retardant polyether polyols (FPMPO) are synthesized and combined with modified expanded graphite (PEG) to prepare the flame resistance flexible polyurethane foam (FFPUF) by one-step method. The results show that the combination of the two catalysts can control the cell structure of FFPUF availably for sound absorption. The FPMPO have little negative influence on the cell morphology and the sound absorption performance of FFPUF, but the increase of flame resistances is finite due to the limited amount of FPMPO. In order to improve the flame retardant properties further, the FPMPO and the PEG are combined in the modification. Benefitting by the effective control structure and the modification with composite flame retardant, the FFPUF shows excellent sound absorption and flame retardant properties. The LOI value of FFPUF is 33.4 and the vertical burning level reaches V-0, and the average sound absorption coefficient maintains 0.68 in the 800-6300 Hz range.

Retraction Note: Sound absorption performance of EPDM-based textile composites investigated through the transfer matrix model

Retraction Note: Sound absorption performance of EPDM-based textile composites investigated through the transfer matrix model

Exploring the acoustic potential of 3D printed micro-perforated panels: A comparative analysis

In the present study, the sound absorption performance of inhomogeneous Micro-Perforated Panels (MPPs) with multiple cavities is investigated. Two models, a three-cavity system and a four-cavity system, are proposed and a numerical study is performed using MATLAB. The models are validated through experimental analysis in an impedance tube. The study meticulously varies the geometrical parameters, including pore diameter, thickness of the MPP, perforation ratio, and back-cavity length. It is found that MPPs with a greater number of sub-cavities have a better sound absorption coefficient than two-cavity systems. The results suggest that the back air cavity is predominantly responsible for multiple peaks, ensuring wideband sound absorption. It is also found that smaller perforation ratios for sub-cavities with larger pore diameters improve sound absorption performance in the lower frequency region. The study indicates that a pore diameter of less than 0.5 mm should be used for better sound absorption above the range of 800–850 Hz, and back cavity length has greater control than pore diameter between 850 Hz and 2000 Hz to make the curve smooth with less fluctuation. The findings have significant implications for the design of MPPs for real-world applications.

Recent advances on the fabrication and application of sound absorption coating-based textile composites

Noise pollution has been considered as a serious threat to the health of humans. The application of sound absorption materials is an effective noise reduction approach. Fibrous materials exhibit the unique micro-structures including small diameter, large specific surface area, and high porosity, which has been widely developed for sound absorption. Recently, rapid growth has been observed in the coating treatment of fibrous based materials and composites for acoustic applications, which can be attributed to the advantages of a facile production process, cost-effectiveness, and good sound absorption capability. This review aims to provide a brief overview on different coating layers of fibrous materials for improved sound absorption properties. The details of various factors affecting the acoustic behavior of coating materials are described. Among them, polymer coating is a widely used acoustic treatment method, adding particles and nanofiber materials to the polymer matrix, and carrying out structural design, which can further improve the sound absorption performance of textile materials. According to the different needs of the application field, different coating treatment methods have their own advantages. In summary, coating materials are promising to be used in buildings and interiors for efficient noise reduction and control.

Research on lignin-modified flexible polyurethane foam and its application in sound absorption

Lignin is a sustainable biomass resource with abundant hydroxyl groups that holds great promise for use as a feedstock for polyurethane foam production. Therefore, the flexible polyurethane foams (FPUFs) were prepared using the oxidized alkali lignin (OAL) as the matrix to enhance its compatibility. The OAL was obtained under the following conditions of 60 °C, 80 min treatment, a ratio of hydrogen peroxide to lignin of 1.2:1, and a ratio of iron hydroxide to lignin of 0.01. It was demonstrated that incorporating OAL enhanced the density, compressive strength, sound-absorbing performance and degradability of foam composites. The compressive strength was also improved by more than five times than that of blank foam under the optimal conditions, reaching 0.11 MPa. The thermogravimetric analysis (TGA) revealed that the foam composite containing 30 % modified lignin content exhibited the highest thermal stability. The results of solvent resistance testing demonstrated the durability of the foam composites in both water and solvents. Lignin-modified polyurethane foam exhibited an acoustic absorption coefficient above 0.2 across a wide frequency range, with the highest value reaching 0.84, meeting the conventional requirements for sound absorption materials (α > 0.2). The results suggested that this environmentally friendly preparation method was feasible for producing high-performance polyurethane foams, which was appropriate for the production of sound absorption boards for industry, transportation by train and automobile.

Self-cleaning, energy-saving aerogel composites possessed sandwich structure: Improving indoor comfort with excellent thermal insulation and acoustic performance

In the context of “carbon neutrality and emission peak”, aerogel that can meet national energy saving and emission reduction requirements while achieving efficient noise reduction has become a hot research topic. However, the development of multifunctional applications is greatly limited by the fact that pure aerogel usually exhibits relatively homogeneous properties. In this paper, SA@UGFW sandwich aerogel composites with functional silanes for structural strengthening were developed. SA@UGFW not only demonstrates ultra-lightweight (58 kg/m3) and high-strength properties (0.1 MPa) but also highly efficient self-cleaning capability (water contact angle ≈ 152.4°). The sandwich aerogel created super-efficient thermal insulation (0.015–0.017 W/(m·K)) and sound absorption performances (αmax = 0.93, NRC = 0.51, 9.77 mm). SA@UGFW exhibited a cold surface temperature of 54.2 ℃ and a ΔT of 145.8 ℃ when the heat source temperature was 200 ℃, despite the sample thickness of only 9.77 mm. At this point, ΔT was higher than 70 % of the heat source temperature. The thermal conductivity of SA@UGFW was as low as 0.00975 W/(m·K), even in −40 ℃ environment. In addition, the sandwich aerogel also showed 0.0204 W/(m·K) of low thermal conductivity following ultra-low temperature (-196 ℃) treatment for 168 h. Simulation results show that aerogel building insulation reduces heating energy savings by 31.00 % and cooling energy savings by 27.34 % compared to traditional insulation. Therefore, the sandwich aerogel with multiple functions reported in this paper achieved the enhancement of indoor comfort and was expected to be widely applied in the construction field.

A controllable foaming approach for the fabrication of “rattan-like” graphene-based composite aerogel with desirable microwave absorption capacity

As a common environmental pollutant, microwave can cause great harms to human health. The development of high-performance microwave absorber with lightweight is indeed necessary. Herein, “rattan-like” graphene-based composite aerogels, having macroscopic pores surrounded by plenty of small pores, were designed and fabricated via an in-situ foaming then carbonized approach. Firstly, graphene oxide (GO), nanocellulose and ferrous ions were integrated into an aerogel with uniform large pores via a freeze-casting method. Then, the aerogel was immersed into a H2O2 solution, during which bubble clusters generated in situ. These bubbles were driven into the stacked GO sheets and formed small pores. With the increase of the H2O2 concentration from 0.5 to 10 wt%, the count percentage of the small pores in the aerogel increased from 81.5 to 95.2%. After the final carbonization, the graphene sheets were dually interconnected with magnetic nanoparticles and carbonized nanocellulose. The unique porous structure and dual-connected networks endowed the aerogel with enhanced conductive loss and optimized impedance matching capacity, and thus an excellent microwave absorption performance, whose maximum reflection loss achieves −68.5 dB. Further, the aerogel also exhibited superior sound absorption performance (noise reduction coefficient up to 0.91 in 1000–6300 Hz), and good mechanical stability.

3D Printed Nature Pattern Metastructure for The Sound Absorption Coefficient

This research investigates the influence of the shape of 3D printed metastructures on sound absorption performance, focusing on three distinct configurations inspired by nature: honeycomb, spiderweb, and gyroid. The objectives involve designing and producing sound-absorbing structures using the 3D printing Fused Deposition Modelling (FDM) method. Simultaneously, the study analyzes and compares their sound absorption performance by considering the sound absorption coefficient and the noise reduction coefficient (NRC) for each pore shape. Using computer-aided software, the three different pore shapes were designed and produced using Polylactic Acid (PLA) material through FDM 3D printing. Each design was replicated at three different thicknesses: 10mm, 20mm, and 30mm, all with a diameter of 94mm. The sound absorption coefficient of the samples was evaluated through impedance tube experiments, collecting data for alpha (α) from 250 Hz to 2000 Hz. Subsequently, NRC values were calculated for four different frequencies: 250Hz, 500Hz, 1000Hz, and 2000Hz, ensuring a comprehensive analysis. Results indicate that the gyroid structure exhibited the highest overall sound absorption coefficient across the tested frequency range, followed by the spider-web and honeycomb structures. Additionally, the 30mm thickness demonstrated greater sound-absorbing performance than the 20mm and 10mm thicknesses. These outcomes provide valuable insights into the sound absorption capabilities of 3D printed metastructures, highlighting the superior performance of the gyroid structure. Understanding the impact of pore shape and thickness on sound absorption performance contributes to the development of acoustically optimized materials for various applications

The sound absorption properties of a double-leaf micro perforated panel (DL-MPP) made from a double-layered polypropylene material.

Micro-perforated panel sound absorbers are recognized as an alternative method for noise control, offering advantages over conventional porous absorbers. However, the sound absorption of a single micro-perforated panel (MPP) is limited in its ability to cover a broad range of frequencies, especially in the low-frequency region. Therefore, the primary focus of this study is to investigate the sound absorption performance of a double-leaf micro-perforated panel (DL-MPP) absorber, which aims to achieve high sound absorption across a wide frequency range. This study examines the impact of varying parameters, including perforation ratio, diameter of perforated holes, and air gap thickness, on the sound absorption characteristics of a polypropylene-based DL-MPP absorber. Polypropylene was used as the sound absorption material for this investigation. The DL-MPP absorber consists of two perforated panels installed parallel to a rigid back wall, with an air gap between them. To assess the sound absorption performance, a prototype of the DL-MPP absorber was fabricated and tested using a two-microphone impedance tube method following ASTM E1050 standard. The results demonstrate that the optimal sound absorption performance was achieved by designing the MPPs with a 1% perforation ratio, 1 mm diameter of perforated holes, and a 1 mm sample thickness.

Sound absorption performance of a micro-perforated plate sandwich structure based on selective laser melting

ABSTRACT This study proposes a sandwich structure of triply periodic minimal surface (TPMS) based on the theory of micro-perforated plates. This structure was processed using laser selective melting (SLM) with the acoustic-vibration theoretical model established through the acoustic-electrical analogy method. The theoretical model was verified by comparison with the experimental results, showing that the micro-perforated plate TPMS sandwich structure exhibited good sound absorption performance with the maximum sound absorption coefficients being higher than 0.8. The micro-perforated plate TPMS sandwich resonated when excited by sound waves. The change in the volume fraction affected the size of the cavity volume behind the micro-perforated plate, thereby affecting the resonance frequency. The increase in volume fraction decreased the volume of the cavity behind the structural plate, the sound absorption performance to increase, the resonance frequency to move towards high frequencies, and the sound absorption bandwidth to decrease. The resonance frequency was negatively correlated with the panel thickness. The increase in the panel thickness increased the maximum sound absorption coefficient and decreased the sound absorption bandwidth when the structure resonated. Also, high-order resonance frequencies appeared when the number of cell layers increased to a certain level.

Acoustic Performance of Porous Mortar and Potential Use for Traffic Noise Mitigation: A Review

Porous mortar (PM) is a porous building material used to reduce noise levels in economic emerging cities to achieve acoustic comfort. This research paper provides a comprehensive review of PM’s sound absorption performance as reported in selected published works. The selection criteria are limited to experiments conducted on specimens with a thickness ranging from 20 to 75 mm, a range suitable for application as a sound-absorbing layer on noise barriers or building walls. This paper explains the underlying principles of sound absorption in PM and outlining methods for assessing sound absorption. This review paper includes the performance of conventional or typical PM with modified PM, considering elements such as mix design and significant factors that influence sound absorption, notably material density, and pore size. Subsequently, this paper reveals on the evaluation of PM’s suitability as a sound-absorbing material, encompassing an assessment of its mechanical properties. In conclusion, the paper identifies the potential of PM as an efficient sound absorber, particularly in the context of mitigating traffic-generated noise.