Acoustic Absorption Performance Research Articles

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.

Prediction of acoustic absorption performance of a perforated plate with air jets

The present study focuses on the prediction of acoustic absorption performance of a perforated plate with air jets by theoretical calculations. In addition, we experimentally measured the flow rate, internal pressure, acoustic pressure, and transfer function using an acoustic impedance tube. The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods. We investigated the influences of background air space, flow velocity, thickness, aperture rate, and aperture diameter of a perforated plate on the acoustic absorption characteristics. The frequency characteristics of the acoustic absorption coefficient showed a maximum value at a local frequency. As the background air space increased, the peak frequency of acoustic absorption characteristics decreased. As the flow velocity passing through the apertures increased, the peak level of the acoustic absorption coefficient also increased. The theoretical results agreed well with the experimental ones qualitatively.

Acoustic absorption of fibro-granular composite with cylindrical grains

This paper reports the influence of cylindrical granular materials on the acoustic absorption performance of a natural fiber composite. The acoustic absorption behavior of an innovative fibro-granular composite composed of natural fibers combined with granular materials was investigated. The fibrous part of this new composite is fabricated using coconut coir fiber and the granular part by cylindrical rice husk grain. This study was motivated by a desire to improve the acoustical performance of materials made from natural (coir) fibers. The amount of binder additive added during composite preparation was considered by reconstructing the equation using fiber diameter as a new parameter. The acoustic properties of the novel composite were investigated based on the well-known Johnson-Champoux-Allard model by varying different physical parameters. The experimental analysis was performed in impedance tube to validate the analytical outcome. The developed analytical model employing Johnson-Champoux-Allard model was found to give predictions in good agreement with absorption coefficient data for the composite material samples with four different thicknesses. The effect of varying the different factors, such as sample thickness, fiber–grain size and fiber-grain ratio, on the acoustic absorption performance and the effect of the binder additive were also investigated. Results confirmed the potential of the new material as a promising acoustic absorber in the low-frequency region (less than 1kHz).

The Development of Novel Sound-Absorbing and Anti-Corrosion Nanocomposite Coating

The effects of addition of graphene on the corrosion protection and acoustic absorption performance of PU coatings have been studied in this paper. The corrosion properties of the coatings were characterized by electrochemical impedance spectroscopy, potentiodynamic polarization curves, and salt spray testing. The acoustic absorption coefficient (α) was measured over the frequency range of 1–8 kHz by two-microphone impedance tube filled with water. The preliminary experimental results showed that PU/graphene nanocomposite coating exhibited a relatively high and stable impedance value during exposure to a 3.5 wt% NaCl for 168 hours, suggesting the presence of graphene can effectively improve corrosion resistance of the PU coating. Also, it was observed that PU/graphene nanocomposite coating had higher acoustic absorption coefficient and exhibited good absorption performance in the frequency range of 1000 Hz and 8000 Hz as the graphene content is 4 wt%.

Influence of Sugar Palm Ash Fraction and Resonator Configuration on Acoustic Absorption Performance of Expose Brick

<span>Sound absorption performance optimization of expose brick has been conducted in associated with <span>the fraction of sugar palm ash in its raw material and configuration of Helmholtz resonators inside <span>the brick structure. The testing was conducted experimentally refer to ASTM E-1050-98 standard <span>procedure. In this case there are three variations sugar palm ash fractions of 0%, 5%, and 10%, as <span>well as two array resonator configurations. The results showed that the brick with fraction of 10% <span>sugar palm ash has the best sound absorption performance. As for the configuration of array <span>identical Helmholtz resonator giving better performance improvement at low frequency span than <span>complex resonator structure with coupled cavity where the best performance occur on(376-488) <span>Hz frequency range with the absorption coefficient α of 0.54.</span></span></span></span></span></span></span></span><br /></span>

The Development of Novel Sound-Absorbing and Anti-Corrosion Nanocomposite Coating

The effects of addition of graphene on the corrosion protection and acoustic absorption performance of PU coatings have been studied in this paper. The corrosion properties of the coatings were characterized by electrochemical impedance spectroscopy, polarization measurements, and salt spray testing. The acoustic absorption coefficient (α) was measured over the frequency range of 1–10 kHz by two-microphone impedance tube filled with water. The preliminary experimental results showed that PU/graphene nanocomposite coating exhibited a relatively high and stable impedance value during exposure to a 3.5 wt% NaCl for 168 hours, suggesting the presence of graphene can effectively improve corrosion resistance of the PU coating. Also, it was observed that PU/graphene nanocomposite coating had higher acoustic absorption coefficient (α) and exhibited good absorption performance in the frequency range of 5000 Hz and 10000 Hz as the graphene content was increased up to 0.2 wt%.

Acoustic Absorption of Natural Fiber Composites

The current study is a bibliographic observation on prevailing tendencies in the development of acoustic absorption by natural fiber composites. Despite having less detrimental environmental effects and thorough availability, natural fibers are still unsuitable for wide implementation in industrial purposes. Some shortcomings such as the presence of moisture contents, thicker diameter, and lower antifungus quality hold up the progress of natural fiber composites in staying competitive with synthetic composites. The review indicates the importance of the pretreatment of fresh natural fiber to overcome these shortcomings. However, the pretreatment of natural fiber causes the removal of moisture contents which results in the decrease of its acoustic absorption performance. Incorporation of granular materials in treated fiber composite is expected to play a significant role as a replacement for moisture contents. This review aims to investigate the acoustic absorption behavior of natural fiber composites due to the incorporation of granular materials. It is intended that this review will provide an overview of the analytical approaches for the modeling of acoustic wave propagation through the natural fiber composites. The possible influential factors of fibers and grains were described in this study for the enhancement of low frequency acoustic absorption of the composites.

Improvement in underwater acoustic absorption performance of open-celled SiC foam

Abstract Open-celled silicon carbide (SiC) foam has been proven of a promising underwater acoustic absorption material. However, further improvement of its sound absorption capacity especially at low frequency is restricted by the acoustic impedance mismatch between the foam material and the water surrounding it. How to tailor the existing SiC foam in order to achieve an optimized impedance match is a key issue. In this work, the underwater acoustic absorption performance of open-celled SiC foam is studied by both analytical and experimental methods. First, based on Zwikker–Kosten’s theory, the modified Johnson–Allard (J–A) model is proposed to analytically predict the absorption performance of liquid-saturated SiC foam. Then three approaches including (i) backing the test samples by a 30-mm-thick air cavity, (ii) enclosing a certain amount of water and (iii) filling the samples with silicon oil are proposed to improve the underwater sound absorption performance of SiC foam. The underwater acoustic absorbency of the silicon oil filled SiC foam is significantly improved, especially in the low frequency band. A sound absorption coefficient near unity is achieved by this manner over a significant portion of the investigated frequency range, eg. 750–4000 Hz. The foam partially filled with water also shows enhanced sound absorbency at low frequency, but the foams backed by air gap and saturated fully by water display degraded sound absorption capacity.

Study on reducing railway noise by porous concrete sound-absorbing panel

This paper investigates the effects of using porous concrete sound-absorbing panels to reduce railway noise. In our experiment, the noise reduction coefficients of porous concrete materials with various aggregate types, gradings, fibre contents and compaction indexes of structure are first measured in the laboratory. The laboratory results show that the porous concrete can effectively absorb acoustics and meet the mechanical standards for wind resistance. Moreover, the grading of the combined aggregate has a significant effect on acoustic absorption performance. The results also indicate that the fibre affects the strength of the porous concrete and the acoustic absorption. The findings from the laboratory study are then used to make porous concrete sound-absorbing panels for a field test. The results indicate that the porous concrete sound-absorbing panel can significantly reduce the railway noise as trains travel at different speeds.

Sound and vibration analysis of a nonlinear panel absorber mounted on an enclosure panel using the multi-level residue harmonic balance method

A thin metal panel absorber is usually mounted on an enclosure panel to enhance its acoustic absorption performance because of its light weight and good durability. Few studies have investigated the sound radiation from an enclosure panel mounted with a nonlinear panel absorber, although there have been many on nonlinear plates, linear structural–acoustic coupling problems, the sound absorption of various panel absorbers, and sound radiation from vibrating structures. In this paper, a multi-structural acoustic modal formulation is derived from two coupled partial differential equations representing the sound radiation from an enclosure panel subject to the acoustic pressure induced by a nonlinearly vibrating panel absorber. The results obtained from the multi-level residue harmonic balance method are in reasonable agreement with those obtained from a numerical integration method. In a parametric study, the panel displacement amplitude converged with an increasing number of modes. The effects of excitation level, damping, aspect ratio, cavity depth, and resonant frequency ratio are examined here. It can be concluded from some of the numerical results that the nonlinear resonances of a panel absorber can increase sound radiation if they are strongly coupled with the linear resonance of the enclosure panel. In other words, the panel absorber deteriorates the enclosure panel’s sound insulation performance.

Modeling and Simulation of Underwater Acoustic Absorption Properties of Novel Macroporous Resins - Elastomer Thin Coatings

In order to improve acoustic stealth performances at high-frequency of underwater objects, macroporous resin beads–elastomer coatings with 2 mm of thickness were introduced for high-frequency acoustic-absorption. Meanwhile, an acoustic model was theoretically built on the transfer matrix method to calculate and analyze the influences of the coating loss factor, density, Young's modulus and the frequency on underwater acoustic absorption properties. Simulation results showed that the acoustic absorption coefficient curves had a periodic change own to the steel plate resonance effect, meanwhile, the greater coating loss factor, the better acoustic absortpion properties; the greater coating density, the better effect of acoustic absorption at low frequencies, but at middle and high frequency. the larger Young's modulus of coating, the smaller the acoustic reflection coefficient and then the better the acoustic absorption performance.

Reducing Railway Noise with Porous Sound-Absorbing Concrete Slabs

The effect of porous sound-absorbing concrete slabs on railway noise reduction is examined in this paper. First, the acoustical absorption coefficients of porous concrete materials with various aggregate types, gradations, fibre contents, and compaction indexes are measured in the laboratory. The laboratory results show that porous concrete that uses a composite of expanded perlite and slag as aggregate can not only obtain good acoustical absorption properties but also satisfy mechanical requirements. Also, the gradation of the combined aggregate has a significant effect on the acoustic absorption performance of the porous concrete, with an optimal aggregate gradation of 1~3 mm. Furthermore, the fibre content and compaction index affect both the strength and the acoustic absorption property of the porous concrete, with the optimum value of 0.3% and 1.6, respectively. Then, the findings from the laboratory studies are used to make porous sound-absorbing concrete slabs, which are applied in a test section. The measurements indicate that porous sound-absorbing concrete slabs can significantly reduce railway noise at different train speeds and that the amount of the noise reduction changes roughly linearly with speed when the train is traveling at less than 200 km/h. The maximum noise reduction is 4.05 dB at a speed of 200 km/h.

Noise Reduction Potential of Cellular Metals

Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined.

Mechanical and acoustic performance of compression‐molded open‐cell polypropylene foams

AbstractOpen‐cell materials are lightweight and multifunctional capable of absorbing acoustic energy and supporting mechanical load. The acoustic and mechanical performance of open‐cell materials can be optimized through processing. In this article, the relationships between processing parameters and acoustic and mechanical performance are shown for polypropylene (PP) foams. PP foam samples are fabricated using a combined compression molding and particulate leaching process. The results from a parametric study showed that both salt size and salt to polymer ratio affect the acoustic and mechanical performance of open‐cell PP foams. As salt size increases, cell size increased and cell density decreased. The salt to polymer ratio had opposite affect on cell density, and increasing the salt to polymer mass ratio increased the open‐cell content. The airflow resistivity decreased significantly by increasing the cell size, which means that foam samples with smaller cell size have better sound absorption. When foam samples were thin, smaller cell sizes produced better sound absorption; however, as thickness of the sample increases, medium cell size offered the best acoustic performance. The compressive strength of the foams was increased by increasing the relative density. Acoustic performance results from the parametric study were compared to the Johnson‐Allard model with good agreement. Finally, optimal cellular morphologies for acoustic absorption and mechanical performance were identified. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

ACOUSTIC ABSORPTION OF MACRO-PERFORATED POROUS MATERIALS

The paper discusses the absorption of non-homogeneous thin macro-porous materials. In particular, the acoustic absorption performance of three-dimensional (3-D) porous media made up from thin porous patches, with different acoustic properties, is investigated using a numerical model. The presented model considers the configuration wherein the material is bonded onto the hard-walled termination of a semi-infinite rectangular waveguide. It couples a finite element description for the porous material to a modal description in the waveguide and uses a power balance approach to accurately quantify the absorption performance of the material. Experimental results are presented to validate the model in the special case of a macro-perforated porous material. Using this model a parameter study is presented. It is shown that absorption may be increased at low frequency by using non-homogeneous patch-works.

Transmission loss of heterogeneous porous materials

Recently, the authors have investigated the acoustic absorption performance of heterogeneous materials made up from a combination of thin porous patches, with different acoustic properties. It has been shown that absorption could be significantly increased in the case of properly designed macroperforated wools in a large frequency band. This paper investigates the transmission loss of similar macroheterogeneous materials. The studied materials are made up of porous elastic materials containing solid inclusions. They are placed into an infinite rectangular waveguide. The numerical model used combines a finite-element formulation for the heterogeneous porous material and a modal description of the acoustic field in the waveguide. The coupling between the solid and the porous patches is accounted for naturally through the use of a modified Biot’s formulation. Numerical results are presented to show the effect of several geometric and physical parameters on the transmission loss performance of heterogeneous porous materials.

Acoustic absorption performance of polyacrylic composite latex

AbstractIn this work, copolymers and a multilayer core/shell P(BA/BA‐MMA/MMA) composite latex of methyl methacrylate (MMA), butyl acrylate (BA), and ethyl acrylate (EA) were prepared by emulsion polymerization. The thermal and the mechanical properties of their films were characterized by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA), while the acoustic absorption performance of dried films were estimated using the standing wave pipe method. The results show that a multilayer core/shell polymer of P(BA/BA‐MMA/MMA) has many glass transitions in a broad temperature region, and in the frequency range of sound, this core/shell polymer has better acoustic absorption properties than the random copolymer of P(BA‐MMA). © 1995 John Wiley & Sons, Inc.