A novel multiscale porous composite structure for sound absorption enhancement

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

Gyroid minimal surface-based composite porous structure with superior mechanical property via triangular grid design and stress distribution optimization

The aramid nanofibrous aerogels (ANFs) have various application prospects due to their ultra-light, high porosity and excellent properties of aramid fibers. However, the preparation of ANFs requires long preparation time and their ultra-dense pore structure leads to poor sound penetration and high sound energy reflectivity, which ultimately makes the overall sound absorption performance of ANFs poor. Therefore, a strategy for synthesis of ANFs is designed to achieve light weight, excellent thermal insulation performance and significantly improve sound absorption properties. This strategy combines cell pulverizing, pump-filtration molding, and directional freezing to ensure structural strength of the aerogel without the addition of cross-linking agents, and this process enables the ANFs to introduce in macro-pores while keeping nano-pores. The structure of multi-layered pores effectively reduces the reflectivity of incident acoustic energy and improves the sound absorption coefficient. The interconnected macro-pores and interlaced small pores of ANFs provide good sound absorption performance (sound absorption average (SAA) = 0.338), excellent flame retardant and thermal insulation properties (thermal conductivity = 0.0635 W (m*K)−1) with ultralight (density = 40.5 mg cm−3) in a thinner thickness (15 mm), which extend the potential of ANFs in areas of noise control and thermal insulation. In addition, the structure of multi-scaled pores can also be formed inside other aerogels by using the method of cell pulverization and filtration preparation, which can be helpful for improving their properties of thermal insulation and sound absorption.

BOOK REVIEW: Electronic Commerce

This paper presents an experimental investigation on the sound absorption behavior and thermal properties of Struto nonwovens by establishing relationship between these properties. Seven Struto nonwoven fabrics were selected to examine the noise reduction coefficient (NRC) and average values of sound absorption coefficients ([Formula: see text]) as well as thermal properties, including thermal conductivity and thermal resistance. The Brüel and Kjær impedance tube instrument and Alambeta were used for the evaluation of acoustic and thermal properties, respectively. The influence of structural parameters on acoustic and thermal properties of Struto nonwovens were investigated and analyzed. The results showed that Struto nonwovens with higher thickness, finer fibers and higher fabric grams per square meter can provide better sound absorption performance. The effect of specific airflow resistance on sound absorption performance was also investigated. It is observed that sound absorption performance has a strong correlation with specific airflow resistance. The effect of porosity on specific airflow resistance and thermal properties was studied in detail. The result indicated that porosity has a strong correlation with specific airflow resistance and thermal properties. It was also observed that sound absorption, the NRC and [Formula: see text] have an insignificant correlation with thermal conductivity, while they are strongly correlated with thermal resistance. The correlation coefficient of the NRC with thermal resistance is 0.9835, indicating that the NRC is directly proportional to the thermal resistance of Struto nonwovens.

Noise pollution is often overlooked and invisible, but it significantly impacts the quality of human life. One of the most straightforward solutions to mitigate noise pollution is by using sound-absorbing materials. Recently, research trends to develop sound absorbing green materials, typically derived from agricultural by-products, have witnessed an uptick. This paper summarizes the sound-absorbing properties of various green materials found in the literature, including coconut fiber, kenaf fiber, rice bran, rice husk, rice straw, Hanji (a traditional Korean paper), tea-leaf fiber, mandarin peel, pineapple-leaf fiber, corn husk, peanut shell, sugar palm trunk, yucca gloriosa fiber, fruit stones, wood barks, flax fiber, and nettle fiber. Natural fibers can be made by compressing the raw material or manufacturing them into fibrous materials or composites. The key variables that determine sound absorption performance are the thickness and density of the green material, as well as the presence of an air back cavity. Generally, thicker materials exhibit better sound absorption performance in the low- and mid-frequency range. Moreover, higher density is associated with better sound absorption performance at the same thickness. Additionally, increasing the distance between the sound-absorbing material and the air back cavity enhances sound absorption performance at low frequencies. Thus, these physical variables, rather than the specific materials used, primarily influence sound absorption capabilities. Therefore, various green materials, such as fibers, granules, and porous materials, can be effective sound absorbers if their thickness, density, and air back cavity are properly controlled.

Noise reduction with materials of finite thickness has been a hot research topic. In this study, multi‐layer gradient fiber‐based composites integrating porous, resonant and damping structures were prepared for efficient sound absorption. Here, the effects of composite structure, fiber‐based thickness and micro‐perforated membrane fabric (MPMF) structure on the sound absorption of the composites were investigated. From the results, the sound absorption band of the composite can be effectively tuned by adjusting the structure of the MPMF or the thickness of the fiber‐based. In addition, the established acoustic model can accurately predict the sound absorption performance of the structure. It is worth mentioning that the gradient structure optimized by the algorithm exhibits broadband sound absorption (noise reduction coefficient of 0.42) and thin feature (thickness of 0.9 cm). Moreover, the medium and low frequency sound waves can be propagated and absorbed more easily by optimizing the structure of the composite. This work provides a reference for the preparation of multi‐layer gradient sound‐absorbing structures and the design of acoustic products in a specific frequency range.

Tunable acoustic composite metasurface based porous material for broadband sound absorption

A multiscale theoretical approach for the sound absorption of slit-perforated double porosity materials

Design, Preparation, and Analysis of the Acoustic Performance of Waste Hemp/PLA Fiber Sound-Absorbing Composites with Different Bionic Structures

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

<sec>Low-frequency noise has always been a thorny problem in the field of noise control. In recent years, the development of sound-absorbing metastructures has provided new ideas for controlling low-frequency noise. In this work, we propose a low-frequency sound-absorbing metastructure constructed by Helmholtz resonators with embedded slit. Analytical and numerical models are established to analyze the sound absorption performance and mechanism of the proposed sound-absorbing metastructure, and optimization design is conducted to achieve low-frequency wideband absorption performance. The analytical modeling method and the performance of the proposed sound-absorbing metastructure are also experimentally verified. The main conclusions are summarized as follows.</sec><sec>1) By using transfer matrix method and finite element method, analytical and numerical models for calculating sound absorption coefficient are established. It is shown that analytical predictions are in good agreement with numerical calculations. It is demonstrated that a typical design of a 30-mm-thick single-cell metastructure can achieve a sound absorption coefficient of 0.88 at 404 Hz. Typical designs of two-cell parallel structure and the four-cell parallel structure (both with a thickness of 50 mm) can achieve two and four nearly perfect low-frequency sound absorption peaks in a frequency band of 200–400 Hz, respectively.</sec><sec>2) The low-frequency sound absorption mechanisms of the proposed metastructures are explained from four aspects: simplified equivalent model parameters, normalized acoustic impedance, complex-plane zero/pole distribution, and sound pressure cloud image and particle velocity field distribution. It is demonstrated that the main sound absorption mechanism is related to the thermal viscous loss of sound waves, caused by the inner wall of embedded slit.</sec><sec>3) The design for broadband low-frequency absorption performance is optimized by using differential evolution optimization algorithm. An optimized parallel-multi-cell coupled metastructure with multiple perfect sound absorption peaks below 500 Hz is realized. For a thickness of 90 mm, the sound absorption coefficient curve of an optimized metastructure exhibits 8 almost perfect sound absorption peaks and an average sound absorption coefficient of 0.86 in a frequency range of 170－380 Hz.</sec><sec>4) Experimental samples are fabricated to test sound absorption. Experimental results are basically consistent with the analytical predictions. The results from analytical model, numerical calculations and experimental measurements are mutually verified.</sec><sec>In summary, the sound-absorbing metastructures with a thickness of sub-wavelength, proposed in this work, exhibit outstanding sound absorption performance at low frequencies. We demonstrate that they are suitable for low frequency broadband sound absorption below 500 Hz. Owing to their thin thickness and relatively simple construction, they have broad application prospects in practical noise control engineering.</sec>

In this study we have fabricated acoustic panel made from composites of coconut husk waste powder and styrofoam resin. The objectives of this study were to prepare the acoustic panel and to study the effect of amount of styrofoam resin and thickness of the panel on the sound absorption performance of the composites sample. The acoustic panel was prepared by varying the amount of styrofoam resin (i.e. 250 g and 300 g) mixed with 150 g of coconut hust waste powder and the thickness of the panel (i.e. 1 cm and 1.5 cm). The total of four samples were characterized for their sound absorption coefficient. The samples were tested at Physics Laboratory, Faculty of Mathematics and Natural Sciences, Sebelas Maret University, Solo. The sample testing results showed that the amount of styrofoam resin used in the making of the composites panel and the thickness of the panel have played important role in improving the sound absorption coefficient of the composites panel. Based on the sample testing results, among all the four acoustic panel samples, the sample with the best preformance in the noise absorption properties was the Sample B-2 with sound or noise absorption coefficient of 0.77698. Additionally, the sample with the lowest noice reflection coefficient value was the sample with styrofoam resin of 250 g and thickness of 1.5 cm (i.e. Sample A-2), which was about 0.39401 at frequency test of 1600 H.

Experimental and numerical study on underwater noise control of multigrooved metasurface coating with antifouling and drag reduction potential

In this study, different types of polymeric layers were coated in different weights (g/m2) on nonwoven fabrics by extrusion process and then, sound absorption and transmission loss properties of each sample were examined. Nonwoven fabrics were produced from polyester (PET) fiber, formed by the carding process and bonded by the needle punching process. These samples were tested between 50-6000 Hz frequency range to reveal the effect of polymer layer type and weight coated on nonwoven fabrics on the sound absorption and transmission loss performance at the low, medium, and high-frequency values. Polymer layers were coated with the weight of 400 gsm and 800 gsm. Nonwoven fabric samples coated with polyethylene or polypropylene layers and nonwoven fabric samples without polymeric coating were tested by using an impedance tube and compared in terms of sound absorption and transmission loss performance. In the test system, two sides of the samples were tested separately. It was seen that the sound absorption performance of the samples changed in case the sound wave was first incident to the polymeric layer or nonwoven layer.