Sound Absorption Characteristics Research Articles

Eco-conscious upcycling of sugarcane bagasse into flexible polyurethane foam for mechanical & acoustic relevance.

This study explores the use of sugarcane bagasse (SCB), a byproduct of sugarcane processing, as a bio-filler in the production of flexible polyurethane foam (FPU), focusing on its benefits for both the environment and the economy. By varying the inclusion of SCB waste from 1 to 6 wt%, the research aims to enhance the FPU's mechanical and acoustic characteristics. Techniques such as Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM) were utilized to analyze the chemical structure and surface characteristics of both SCB and the FPU/SCB composites. Additionally, tests on gel fraction, density, and mechanical properties were conducted. The results indicate that adding 4 wt% SCB to FPU considerably improved the foam's properties. This modification resulted in a 148.63% increase in apparent density, a 228.47% rise in compressive strength, and a 116.24% boost in tensile strength. Furthermore, sound absorption across various frequency ranges was enhanced compared to the control foam. Additionally, the findings show that SCB effectively shifts sound absorption characteristics to lower frequencies. Specifically, at a low frequency of 500 Hz, the sound absorption coefficient increased to 0.4 with a foam thickness of 20 mm. This demonstrates that SCB can significantly improve FPU's performance, making it an attractive option for applications requiring noise mitigation, such as in the automotive and construction industries, thereby offering a sustainable solution to waste management and materials innovation.

Enhancing the absorption performance of minimal surface-based bulk absorbers via symmetry-breaking

The examination of Triply Periodic Minimal Surfaces (TPMSs) in the context of their acoustic dampening qualities has established them as viable alternatives to conventional porous absorbers. By adjusting the structure's porosity, one can significantly alter the TPMSs' acoustic absorption characteristics. Traditionally, enhancing sound absorption has involved decreasing porosity, which unfortunately increases the material's weight. In this study, we introduce a different approach to alter their absorption performance without altering their overall relative density. Our approach relies on leveraging the mathematical formulation of such structures to break their underlying geometrical symmetry. This symmetry-breaking results in altering their sound absorption characteristics while introducing an anisotropic acoustic response. In this paper, we present the mathematical design and fabricate the samples using the Fused Filament Fabrication (FFF) additive manufacturing method. The sound absorption characteristics of the printed samples are tested using a two-microphone normal incidence impedance tube setup. The presented results demonstrate that symmetry-breaking provides a viable route towards improving the low-frequency response of TPMS sound absorbers.

The two-cavity method for characterizing acoustical materials-an interlaboratory study

The study focuses on understanding the sound absorption and transmission characteristics of porous acoustical materials, which are determined by two key parameters independent of material thickness: characteristic impedance and propagation constant. These parameters can be characterized by testing a porous sample concept in a normal incidence impedance tube using either the two-thickness or the two-cavity method. In the two-thickness method, two samples of varying thicknesses are required. In contrast, the two-cavity method requires testing one sample at two air cavity depths. This method is particularly advantageous for materials that are costly or challenging to fabricate. This interlaboratory study evaluates the variability of characteristic properties determined using the two-cavity method. Porous acoustical materials were additively manufactured and tested in the Liner Technology Facility at NASA Langley Research Center and the Mechanics, Acoustics and Dynamics Lab (MADLab) at Michigan Technological University. The characteristic properties, derived from various cavity depth combinations, were used to predict the sound absorption curves of the sample with a rigid backing. These predictions were then compared with actual experimental absorption curves. The findings indicate that both the combinations of cavity depths and the sample's static airflow resistivity significantly influence the accuracy of the deduced properties.

Sound transmission loss and energy absorbing performance of stiffened doubly-curved shells with corrugated-honeycomb hybrid cores

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier's techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06 dB within the broad low-frequency range of 380–2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m3, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Sound Absorption Performance of Ultralight Honeycomb Sandwich Panels Filled with "Network" Fibers-Juncus effusus.

This study investigates lightweight and efficient candidates for sound absorption to address the growing demand for sustainable and eco-friendly materials in noise attenuation. Juncus effusus (JE) is a natural fiber known for its unique three-dimensional network, providing a viable and sustainable filler for enhanced sound absorption in honeycomb panels. Microperforated-panel (MPP) honeycomb absorbers incorporating JE fillers were fabricated and designed, focusing on optimizing the absorber designs by varying JE filler densities, geometrical arrangements, and MPP parameters. At optimal filling densities, the MPP-type honeycomb structures filled with JE fibers achieved high noise reduction coefficients (NRC) of 0.5 and 0.7 at 20 mm and 50 mm thicknesses, respectively. Using an analytical model and an artificial neural network (ANN) model, the sound absorption characteristics of these absorbers were successfully predicted. This study demonstrates the potential of JE fibers in improving noise mitigation strategies across different industries, offering more sustainable and efficient solutions for construction and transportation.

Sound transmission loss and energy absorbing performance of stiffened doubly-curved shells with corrugated-honeycomb hybrid cores

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier’s techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06dB within the broad low-frequency range of 380-2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m3, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Underwater sound absorption characteristics of water-saturated porous materials

In this research, the underwater sound absorption performance of porous media saturated with water is investigated through long straight tubes (LSTs) with circular cross-section and sintered fibrous metals (SFMs) containing complex pores, and effective underwater sound absorption capability is demonstrated theoretically, numerically and experimentally. Specifically, the theoretical model for LSTs, verified by direct numerical simulations (DNSs), reveals that much smaller pore diameter and much larger layer thickness of porous material is needed to gain high waterborne sound absorption coefficient than to obtain large airborne sound absorption coefficient. Besides, to examine the sound absorption capacity of realistic porous materials, SFMs backed with a finite cavity are experimentally measured under 7 different hydrostatic pressures in a water-filled tube, and numerically characterized via multi-physics couplings. Insensitivity of effective sound absorption capability to high pressure is established, which stems from the different underwater wave energy consumption mechanism (i.e. viscous-thermal effect) of porous materials from conventional rubber kind of underwater sound absorption materials. Physically, porous materials possess great potential in developing the next generation of high-performance underwater sound absorption materials.

Underwater sound absorption characteristics of water-saturated porous materials

In this research, the underwater sound absorption performance of porous media saturated with water is investigated through long straight tubes (LSTs) with circular cross-section and sintered fibrous metals (SFMs) containing complex pores, and effective underwater sound absorption capability is demonstrated theoretically, numerically and experimentally. Specifically, the theoretical model for LSTs, verified by direct numerical simulations (DNSs), reveals that much smaller pore diameter and much larger layer thickness of porous material is needed to gain high waterborne sound absorption coefficient than to obtain large airborne sound absorption coefficient. Besides, to examine the sound absorption capacity of realistic porous materials, SFMs backed with a finite cavity are experimentally measured under 7 different hydrostatic pressures in a water-filled tube, and numerically characterized via multi-physics couplings. Insensitivity of effective sound absorption capability to high pressure is established, which stems from the different underwater wave energy consumption mechanism (i.e. viscous-thermal effect) of porous materials from conventional rubber kind of underwater sound absorption materials. Physically, porous materials possess great potential in developing the next generation of high-performance underwater sound absorption materials.

Технология изготовления образцов из композитных материалов для проведения лабораторных испытаний

Based on the accumulated experience of the staff of the Institute of Marine Technologies, Energy and Transport of the Astrakhan State Technical University, the development of the production of various parts of ship hulls, elements of main and auxiliary power plants, including various fasteners and stanchions, using additive technology and other methods of forming composite materials has begun. During the implementation of the developed direction, issues arise of reducing the cost, weight of manufactured parts and improving the characteristics of sound absorption, sound insulation, vibration isolation, etc. Despite the fact that adhesives based on epoxy or polyester resin, according to technical documentation, are fast-curing adhesives, they are not applicable for the production of products using three-dimensional printing technologies. for several reasons. The factors preventing the use of materials for the production of such parts are listed: the minimum curing time of one layer of glue under optimal conditions is from one and a half hours or more, which significantly increases the interlayer time interval; the glue layer is not a self-supporting structure due to the fact that it is in a liquid state during the induction period; products made of this adhesive without reinforcement cannot withstand the required dynamic loads. In the process of experimental studies, a number of formulations based on polyester resin with different fillers were obtained, which have the necessary consistency to apply layers on top of the previous one without waiting for curing, and also contain the necessary amount of reinforcing material and other fillers required to solve problems related to vibration isolation and sound insulation.

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.

Sound absorption design and characteristics of variable-section perforated double-porosity multiscale aerogel

A constant-section perforated double-porosity multiscale porous material (CDMPM) introduces periodically distributed straight mesoperforations in an appropriately selected traditional single-porosity substrate. In this work, the effects of mesopore radius ([Formula: see text]) and mesopore height ([Formula: see text]) on the sound absorption performance are numerically investigated using graphene-polyvinyl alcohol aerogel (GPA-1) as a microporous substrate. The findings indicate that adjusting mesopore parameters enables to tune the frequency band and thereby enhancing sound absorption performance. However, CDMPM exhibits insufficient performance in broadband and low-frequency application scenarios. To address this issue, a variable-section perforated double-porosity multiscale porous material (VDMPM) with stepped mesopore profile is proposed via the combination of CDMPMs with different perforation parameters. The influence of multiscale design parameters on the sound absorption characteristics of VDMPM is studied, and the key parameters are adjusted based on CDMPM. The optimized design demonstrates global acoustic characteristics, with absorption peaks at low frequencies and efficient broadband absorption in the mid-to-high frequency range. The stepped mesopore profile of VDMPM induces a sophisticated pressure diffusion effect and expands the energy dissipation region. Finally, the applicability of the proposed perforation strategy is examined using rockwool and melamine foam as alternative microporous substrates. The findings of this research provide practical principles to guide the multiscale structural design of double-porosity materials and to ensure effective enhancement of sound absorption performance of traditional porous materials.

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.

Acoustic characterisation of chair absorption and simple methods for predicting occupied states

The current knowledge of the sound absorption characteristics of chairs is insufficient for a comprehensive understanding, as the sound absorption ranges of chairs and auditors are limited and obtained using several different measurement techniques. In this study, the absorption characteristics of chairs occupied by realistic scale-model auditors are systematically investigated based on the ISO 354 standard method, considering the available maximum variations in the amount of sound absorption, structure of chairs, and clothing worn by auditors. A series of 1/15-scale reverberation room measurements are performed to investigate the effects of the seat position, underpass and backrest heights, and amount of clothing on the sound absorption coefficients for both unoccupied and occupied chairs. In addition, using a wide range of measured data, simple and practical prediction models are proposed to determine the sound absorption coefficients of occupied chairs based on the unoccupied state for both known and unknown auditor characteristics. The validity of the prediction models is evaluated through comparison with the measured results in full- and reduced-scale reverberation rooms, and the comparison results confirm that the predicted absorption coefficients of occupied chairs are in good agreement with the measured values. The application range for the proposed models should be limited to P/A = 1.34 m-1, which is approximately 20 chairs in a general reverberation room.

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 Characteristics of Unsaturated Porous Material Calculated by Modified Transfer Matrix Method

Porous materials have emerged as one of the most widely employed sound-absorbing materials in practical applications, owing to their excellent sound absorption properties and lightweight nature. Unsaturated porous materials have the potential to achieve superior sound absorption effects and significantly reduce mass. However, current research on the sound absorption performance of unsaturated porous materials is limited. This paper used a modified transfer matrix method (MTMM), which relies on matrix dimensionality reduction, to analyze the sound absorption characteristics of unsaturated porous materials under various boundary conditions. The study also examines the impact of different parameters, such as material thickness and saturation, on sound absorption performance and compares the results. The findings indicate that when a solid elastic plate is attached to an unsaturated porous elastic plate, the absorption coefficient decreases while the transmission loss increases. Additionally, reducing the thickness of the plate and increasing its porosity and saturation levels lead to an increase in the absorption coefficient and a decrease in the transmission loss.

An investigation of sound absorption characteristics of Cocos nucifera fiber composite using Taguchi design

An investigation of sound absorption characteristics of Cocos nucifera fiber composite using Taguchi design

Sound Absorption Characteristics of Integrated Membrane-Fabric Materials

Noise pollution has emerged as one of the most important environmental issues, particularly in developing countries. The use of sound absorption material has proven to be a successful approach for minimizing and controlling noise levels. Combining a membrane or panel with two or more porous materials is a practical approach for sound absorption. However, it often makes the absorber thicker, taking up more space and increasing production costs. This research proposes a new integrated sound absorber that combines a rubber membrane with a fabric to absorb sound at different frequencies. The new material eliminates bulky porous materials, saving space and production costs. By varying perforation sizes, percentages, and backed air gap distances, the study investigates the sound absorption characteristics of the integrated membrane-fabric material. The research has determined that the integrated membrane-fabric material exhibits exceptional sound absorption performance across a wide frequency range, which is influenced by several factors, including the diameter and ratio of perforations, and the depth of the air cavity. Furthermore, the investigation revealed that the positioning of the fabric also plays a crucial role in determining the material's absorption performance.

Sound absorption properties of the metamaterial curved microperforated panel

This paper proposes a metamaterial that utilizes resonators to enhance the sound absorption capacity of the curved microperforated panel (CMPP), and reliable theoretical analyses and experimental verification are comprehensively given. A metamaterial curved microperforated panel (MCMPP) absorber is formed by attaching local resonators on the CMPP. The displacements of the midplane of the curved panel are expanded into the improved Fourier series based on Spectral-Geometry Method (SGM), and the vibration equations of the MCMPP are derived by the Rayleigh-Ritz method. The sound absorption characteristics of the MCMPP are solved by the effective medium method and the acoustic-electric analogy method. Both a structure-acoustic coupling simulation model and an impedance tube test system are established to validate the accuracy of the present theoretical model. The essential parametric analyses are carried out in conjunction with mode splitting and acoustic-vibrational coupling, and the results show that the local resonance absorption peak within 1000 Hz increases from 1 to 5 with the absorption coefficients greater than 0.8 at these peaks under the installation options of the periodic gradient array and multiple resonances, realizing the effective absorption in multiple frequency bands. This paper provides theoretical support and experimental protocols for the design and application of the metamaterial curved microperforated panel.

Theoretical estimation of sound absorption characteristics in a collection of rectangular holes: Comparison with experimental results

This study quantifies the sound absorption properties of small rectangular or square pores that are less than a few millimeters per side, based solely on their geometric dimensions. Analytical solutions for the sound absorption coefficient of narrow tubes with rectangular holes have not been obtained. Therefore, alternative methods of predicting the sound absorption coefficient, such as using the circular tube approximation or the two-plane approximation, are possible. In this study, the sound absorption coefficient was estimated by several theoretical models that are considered useful for estimating the sound absorption coefficient in rectangular tubes. The results were then compared with experimental values. For square holes, the accuracy of the sound absorption coefficient increased in the order of the model considering two-sided circumference only, the circular tube model, and Allard's method based on Stinson's. In rectangular holes, Allard's method based on Stinson's showed good agreement with the experimental data across a wide range of aspect ratios. For rectangular holes, the accuracy of Stinson's two-plane approximation was superior to that of the circular tube approximation when the aspect ratio was 4. Furthermore, when the aspect ratio was 8, the accuracy of Stinson's two-plane approximation became comparable to that of Allard's method based on Stinson's.

Tunable underwater sound absorption characteristics of 0-3 piezoelectric anechoic coating.

Piezoelectric composite materials (PCMs) with shunt damping circuits are used widely in hydroacoustics because of the flexible adjustability of their parameters. PCMs offer good underwater sound absorption, but shortcomings remain, such as poor low-frequency sound absorption, narrow bandwidth, and a single dissipation mechanism. In this paper, the tunable underwater sound absorption of a 0-3 PCM combined with a cavity structure and shunt circuit (PCMC) is studied systematically. First, the equivalent material parameters of 0-3 PCM are derived based on the Yamada model, and then a theoretical electroacoustic model is established for solving the absorption coefficient and is mutually verified with the numerical simulation method. On this basis, the tunable absorption characteristics of the structure are analyzed. The results show that coupling the energy dissipation mechanism of 0-3 PCM with the acoustic mechanism of the cavity structure not only achieves strong absorption at lower frequencies but also enriches the absorption mode in the mid-high frequencies by connecting the shunt circuits. Moreover, the influence of piezoelectric control variables and acoustic cavity morphology characteristics on structural sound absorption performance is further explored. Finally, the acoustic performance of PCMC is improved further via shape optimization and parameter optimization.