Acoustic Absorption Performance Research Articles

Analysis on the influence factors of the acoustic absorption performance of porous fiber materials

Porous fiber materials are the most widely used acoustic absorption materials at present, and they have excellent acoustic absorption performance. This paper uses the finite element method to explore the factors affecting the acoustic absorption performance of porous fiber materials, including flow resistance, thickness of the porous fiber material, incidence angle, and back cavity thickness. Due to the complex acoustic absorption mechanism of porous fiber materials, an equivalent fluid model is used to simulate the acoustic absorption properties of the porous fiber materials. The correlation of acoustic absorption performance and the model of the back cavity was analyzed. An impedance tube test was implemented to verify the simulation results.

Relation between Flow Field and Acoustic Absorption Performance of Perforated Plate

Relation between Flow Field and Acoustic Absorption Performance of Perforated Plate

Three-dimensional acoustic energy flow from rotating sound sources

A detailed study of the three-dimensional sound fields around a monopole point source in subsonic and supersonic rotation is investigated. We calculate the sound pressure, the acoustic velocity, as well as the instantaneous and time-averaged acoustic intensity fields with the advanced time approach. The advanced time approach is applied for sound sources at subsonic and supersonic rotation and yield comparable results as those obtained from the spherical harmonic series expansion method or the solution of the retarded time equation. Further, the direction of the time-averaged acoustic energy flow is derived from the acoustic intensity vectors. It is shown, that the direction of the energy flow path differs from the radial direction and depends on the rotational direction and rotational velocity. Those findings are useful, for example, to improve the acoustic absorption performance of sound absorbers and acoustic liners around turbomachines.

Effect of Flow and Hole Shape on Acoustic Absorption Performance of Perforated Plate

Effect of Flow and Hole Shape on Acoustic Absorption Performance of Perforated Plate

Effect of Thickness and Perforation Size on the Acoustic Absorption Performance of a Micro-Perforated Panel

In current times, noise pollution is especially apparent in urban areas due to rapid development in transportation, industrialization, and urbanization. The worsening noise pollution is detrimental to human health and behaviour as it can contribute to disorders and psychological disturbance. Thus, noise regulation is crucial and must be addressed with immediate effect. Micro-perforated panels (MPP) can be a potential solution to mitigate noise on a commercial scale. Researchers have addressed the mechanics behind the enhancement of acoustic absorption through micro-perforation and some suggestions have been made, such as the effect of structural variation on sound absorption performance. Hence, this research aims at optimizing the sound absorption performance of an MPP by determining the connection between thickness and perforation size with sound absorption coefficient. Three cases were considered: (i) varying perforation size, (ii) varying thickness, and (iii) varying perforation size and thickness simultaneously. Based on the Maa prediction model, the sound absorption performance for all three cases have been simulated through the MATLAB software. Results show that the increase in both thickness and perforation size together increases the peak value of sound absorption coefficient (SAC). It also shifts the peak towards the higher frequency region and narrows the bandwidth. The findings of this study indicate the potential of thick MPPs as commercial sound absorbers by adjusting the size of perforations. Thicker and sturdier MPPs with optimal acoustic resistance and reactance can act as reliable sound absorbers for sound insulation purposes.

Bio-based ultra-lightweight concrete applying miscanthus fibers: Acoustic absorption and thermal insulation

Acoustic and thermal comfort play an important role in the building environment. This study investigates ultra-lightweight concrete incorporating Miscanthus fibers as lightweight aggregates to improve sound absorption and thermal insulation properties. Miscanthus fibers (MF) is a kind of sound absorption biomass that can dissipate sound noise thanks to its porous and flexible inner structures and fibrous shape. However, its acoustic absorption performance in cement-based materials is rarely investigated. Therefore, the acoustic absorption and thermal insulation of ultra-lightweight Miscanthus concrete (ULMC) is investigated using two different kinds of Miscanthus fibers. Meanwhile other mechanical properties were characterized, including bulk density and flexural strength. Results showed ULMC with 30% 2–4 mm MF obtained an ultra-low density (554 kg/m3), thermal conductivity (0.09 W/(m·K)) and high acoustic absorption coefficient (0.9) at low frequencies. It is found that the acoustic performance of ULMC can be improved by optimizing the dosage and shape of Miscanthus fibers. The developed green and sustainable bio-based ULMC possesses an excellent acoustic absorption and thermal insulation and is very suitable to use as indoor ceiling boards and in non-structural walls to make indoor living environment comfortable and energy-saving.

An underwater metamaterial for broadband acoustic absorption at low frequency

In order to study and further develop underwater acoustic absorption structures, we present an underwater metamaterial for broadband acoustic absorption in this study, which is composedof viscoelastic rubber, conical cavity, cylindrical oscillator and backing steel. Basis for design is the contribution of local resonance resonators to low frequency absorption of airborne sound. The accuracy of finite element calculation (FEA) is verified by the theoretical model established by transfer matrix (TM) method at radial coordinates. Relative to pure viscoelastic rubber and traditional cavity acoustic absorption structure, the proposed structure could show excellent broadband acoustic absorption performance below 10 kHz. The geometrical size, shape, and position of filler also affect the direction of shear wave propagation after the transformation, which is critical reason behind the broadband underwater acoustic absorption. Different geometries and material parameters also could adjust the acoustic absorption to a great extent. Underwater impedance tube experiment proves the correctness of the FEA and TM calculation results. These conclusions could potentially be used to the underwater acoustic absorption structure.

Estimation and uncertainty analysis of fluid-acoustic parameters of porous materials using microstructural properties.

This study quantified the microstructure of polyurethane foams and elucidated its relationship to fluid-acoustic parameters. The complex morphology derived from the three-dimensional images obtained by micro-computed tomography was analyzed using digital image processing and represented by a pore network model (PNM) and a distance map model. The PNM describes the fluid phase of a porous medium with equivalent spherical pores and circular throats, whereas the distance map model describes the solid phase with the average frame thickness. The porous materials were then modeled by six representative microstructural parameters that describe the geometry and topology of the fluid and solid phases. These parameters were pore radius, throat radius, distance between adjacent pores, coordination number, pore inclination angle, and frame thickness. Semi-phenomenological and empirical approaches were proposed to relate the microstructural properties to the fluid-acoustic parameters. These models effectively described the acoustic parameters and sound absorption performance of six different polyurethane foams. Since the representative microstructural parameters were obtained from small sample volumes of a heterogeneous material, notable variations were observed across different regions of the sample. Hence, this study quantified the effect of the uncertainty in each microstructural parameter on the resulting acoustic parameters using global sensitivity analysis.

Recycling of magnesium waste into magnesium hydroxide aerogels

Abstract The development of magnesium (Mg) production has led to an ever-increasing volume of magnesium waste, with detrimental effects on the environment. Recycling magnesium waste into magnesium hydroxide (MH) aerogels has been successfully developed to partially solve the problem of magnesium waste. The effects of the Mg concentration on the properties of the MH aerogel have been investigated. The MH aerogel exhibits a porous structure with a low density of 0.081–0.150 g cm−3 and a high porosity of 91.5–94.4 %. Its thermal conductivity and stability are evaluated, showing that the MH aerogel has a good thermal insulation capability with a low thermal conductivity of 30–42 mW m-1 K-1, and it is stable up to 800 °C for about 50 % weight loss. In addition, its acoustic absorption performance is also investigated. The MH aerogel performs a good acoustic absorption capability at low frequency, and its noise reduction coefficient indicates that the MH aerogel is a potential competitor to other acoustic insulators. The results demonstrate that magnesium waste can be recycled into a high-value material for thermal and acoustic insulation applications, enhancing the use of environmental wastes.

Study on acoustic properties of multilayer impedance materials

Composite materials are produced using advanced material preparation techniques to optimize a combination of materials with different properties to form new materials. Such materials have the composite properties of their constituent materials. Composite materials have been widely explored for their use in the field of acoustic noise reduction as well as in automobile, aviation, and other fields. To further enhance the acoustic characteristics of composite materials, this letter proposes a multilayer composite structure comprising a resistive screen structure material (perforated screen material), foam, and fiber. The impedance tube method is used to investigate the rigid wall absorption performance and flow field transmission loss in seven types of resistive screen composite materials of various flow resistivities and porosities. The results show that the acoustic absorption and acoustic insulation performance of the resistive screen composite material are better than the foam–fiber multilayer material. The maximum acoustic absorption coefficient reached 0.95 at 3000 Hz and the maximum difference in sound reduction was 6.5dB. This resistive screen material provides a new dimension to the design of new materials.

Theoretical and Experimental Study to Investigate the Acoustic Absorption Performance of Natural Luffa Fibers

Theoretical and Experimental Study to Investigate the Acoustic Absorption Performance of Natural Luffa Fibers

Investigation of effective factors of woven structure fabrics for acoustic absorption

Textiles have been used as noise reduction materials in construction, automotive and other industries for its performance of porous, light and easy processing, but few studies have been done on the sound absorption properties of woven fabrics. In this study, effect of structural factors of woven fabrics on acoustic absorption was investigated. Fabrics with plain, twill and honeycomb weave were weaved with identical warp density and employed as the samples for acoustical measurement, which were measured with acoustical detecting platform based on impedance tube. A novel date processing method was constructed to evaluate the acoustic absorption performance of the woven fabrics. The results show that there is no significant correlation of fabric sound absorption performance with fabric thickness, surface density and porosity. This indicated that the mechanism of acoustic absorption of woven fabrics may dissimilar with the one in other kind of fiber aggregates, such as felts and nonwovens. Although pore characteristics are important factors affecting the acoustic properties of woven fabrics, the effect of pore characteristics on acoustic absorption of textiles cannot be simple attributed to porosity. The size and shape of the pores may also play an important part on sound absorption performance of woven fabrics.

Sound Absorption Property of Polyurethane Foam with Polyethylene Fiber

Flexible polyurethane (PU) foams with varying polyethylene fiber contents were synthesized to improve their acoustic performances. The purpose of this study was to investigate the effects of different polyethylene fiber contents of the PU foams on the resultant sound absorption, which was characterized by the impedance tube technique to obtain the incident sound absorption coefficient. Other parameters related to acoustic absorption performance of polyurethane foams were also measured such as microstructure, porosity and airflow resistivity. In this paper, these parameters were analyzed and compared with those of pure polyurethane foam. The results showed that the acoustic absorption properties of the PU foams were improved especially in the low frequency region by adding polyethylene fiber. When 0.2 g polyethylene fiber was added into the PU foam composite, the sound absorption coefficient is best especially around 125 – 315 Hz. The maximum enhancement in the acoustic properties of the PU foams was obtained by adding 0.1 g polyethylene fiber.

Mechanical, acoustic, and thermal performances of shear thickening fluid–filled rigid polyurethane foam composites: Effects of content of shear thickening fluid and particle size of silica

ABSTRACTShear thickening fluid (STF) features a rheological property, and rigid polyurethane (PU) foams feature low thermal conductivity and excellent acoustic insulation. In this study, an STF/PU rigid foam composite sandwich structure was designed using different contents (0, 0.5, 1, or 1.5 wt %) of STF that contained 14 nm, 40 nm, or 75 nm silicon dioxide (SiO2). The effects of STF content and silica size on the cell structure, mechanical performance, acoustic absorption, and thermal performance of the STF/PU foam were explored. The test results show that STF/PU foam exhibited three characteristic acoustic absorption peaks, and the maximum acoustic absorption coefficient reached 0.841. STF addition increased compression, bending strength, and maximum acoustic coefficient, as well as initial mass loss temperature. STF‐filled PU foam composites containing 14 nm and 40 nm SiO2 had a mild rise in thermal insulation. The rigid STF/PU foam composites with a cell structure had the maximum thermal conductivity of 0.22 W m−1 K−1 and sound absorption coefficient of 0.841, which confirm that they are a good candidate for sound‐absorbing energy conservation materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47359.

Novel implementation of natural fibro-granular materials as acoustic absorbers

In this study, a new innovative fibro-granular composite was prepared as a natural acoustic material by combining fibrous and granular materials. Delany–Bazley model and Biot–Allard techniques were utilized to estimate the absorption coefficient of the developed composite material. The predicted values were validated through an analytical outcome employing Johnson–Champoux–Allard technique and an experimentally measured value which were conducted in an impedance tube. The outcomes showed the reflection of the good agreement between the analytical and experimental methods. The current research concluded that the introduction of granular materials provides significant contribution in enhancing the surface area within the composite, thereby achieving a promising acoustic absorption in the low-frequency region which is below 1 kHz. In addition, the current research also reports that, like Johnson–Champoux–Allard model, Delany–Bazley and Biot–Allard models are also two efficient analytical tools for predicting the significant low-frequency acoustic absorption performance of a fibro-granular composite.

Comparison Sound Absorption Methods of Multilayer Micro-perforated Panels

Micro-perforated panel (MPP) absorbers as the next-generation sound absorbers are getting more widely use in aviation, automobiles, construction and other fields. It’s a complex problem to predict the acoustic performance using surface impedance methods. The acoustic absorption performance of micro-perforated panels were compared in terms of Transfer matrix method and Equivalent electric circuit approach (EECA). The calculated results show that transfer matrix method is more convenient and effective than the equivalent circuit approach especially to multiply layer micro-perforated absorbers.

Open-cell poly(vinylidene fluoride) foams with polar phase for enhanced airborne sound absorption

Open-cell foams of polyvinylidene fluoride (PVDF) homopolymer were fabricated with the content of polar phase being changed by thermal treatment, and their airborne acoustic absorption performance properties were measured comparably in an acoustic tube. The experimental results showed that the sample with the more polar phase and hence a stronger local piezoelectric effect exhibited a significantly larger acoustic absorption coefficient. In addition to the conventional visco-inertial, thermal and materials damping effects, our analysis indicated that the thin and polar struts of PVDF foams with the polar phase and the local piezoelectric effect may further enhance the mechanical damping by converting the excited mechanical vibration to electricity through the local piezoelectric effect and increasing the friction and viscous loss at the fluid-solid interface in the presence of electrical charges. The open-cell polymer foams with high content of the polar phase and the local piezoelectric effect have great potential for passive airborne noise mitigation applications.

Acoustic performance and microstructural analysis of bio-based lightweight concrete containing miscanthus

Miscanthus Giganteus (i.e. Elephant Grass) is a cost-effective and extensively available ecological resource in many agricultural regions. This article aims at a fundamental research on a bio-based lightweight concrete using miscanthus as aggregate, i.e. miscanthus lightweight concrete (MLC), with the special focus on the acoustic absorption property and interaction between miscanthus and Portland cement hydration. The effects of the content, particle size and treatment of fibers on the performance of MLC, including the flowability, strength and acoustical properties, are investigated. Furthermore, the effect of miscanthus on cement hydration is analysed by isothermal calorimetry, X-ray Diffraction, thermogravimetry, and scanning electron microscopy. It is demonstrated that the sound absorption of MLC is dramatically improved with the increasing content of miscanthus. The results show that there is a certain amount of closed internal pores in the composites, which contribute to this enhanced acoustic absorption performance.

Microstructure-based experimental and numerical investigations on the sound absorption property of open-cell metallic foams manufactured by a template replication technique

The current study investigates the acoustic absorption property of nickel-based superalloy open-cell foams manufactured by a newly developed template replication process. Inconel 625 open cell foams with controllable porosities (92%–98%) and cell sizes (300μm–900μm) have been successfully produced and tested for their sound absorption performance. It is evident that foam samples with the smallest cell size among them exhibit the best acoustic absorption performance, with sound absorption coefficient>0.9 at frequencies >1500Hz for 50mm thick sample. In the numerical simulation, the classical Delany­Bazley model is employed to predict the acoustic absorption property across a broad frequency range, and it requires knowledge of foam's static air flow resistivity, which, as proposed in this work, can be analytically expressed as a function of foam's microstructure parameters. A good agreement between such microstructure-based numerical model and experimental results was obtained. The proposed model can be utilized as a material design tool to guide the production of foam with optimal microstructure for sound absorption through the controllable template replication process.

High-temperature acoustic properties of porous titanium fiber metal materials

The high-temperature acoustic absorption performance of porous titanium fiber material was investigated in terms of sample thickness, porosity, temperature, air-cavity thickness and double-layer structure arrangement. The effects on absorption coefficient were systematically assessed. The results show that the sound absorption performance is improved by increasing the sample porosity and/or thickness, and/or increasing the air-cavity thickness. Meanwhile, increasing the temperature gives better acoustic absorption performance in the low frequency range but also lowers the performance in the high frequency range, while double-layer structure enables better acoustic absorption performance.