Determination of the Sound Absorption Capacity of Hydraulic Concrete Mixtures Added with Waste Tire Rubber

There are different types of pollutants that are harmful to the environment, including smog, chemicals that are dumped into rivers, scrap tires, etc. The latter have the particularity that it is not possible to recycle them to manufacture new tires. In the present work, hydraulic concrete plates added with waste tire rubber were manufactured to modify their sound absorption capacity. It was found that the rubber additions produce changes in the density of the material and in the sound absorption capacity. When the material is exposed to high-frequency sounds that correspond to high-pitched sounds, its absorption capacity increases. On the contrary, when the test frequency is low, that is, bass sounds, the sound absorption capacity decreases. The results obtained in this work suggest that the proposed mixtures are suitable for the possible manufacture of acoustic insulating shields.

Development of a High Sound Absorption Material CEMCOM

Based on sound absorption mechanism of material,the special sound absorption material CEMCOM for road sound insulation is introduced.This high sound absorption material is mainly composed of expanded perlite.Using multiple sound absorption structure can improve sound absorption property of material.According to the preparation principle and durability design of material,a new kind of material with low cost and high durability is developed.

Optimization of Sound Absorption and Insulation Performances of a Dual-Cavity Resonant Micro-Perforated Plate

This study investigates a dual-cavity resonant composite sound-absorbing structure based on a micro-perforated plate.Using the COMSOL impedance tube model,the effects of various structural parameters on sound absorption and sound insulation performances are analyzed.Results show that the aperture of the micro-perforated plate has the greatest influence on the sound absorption coefficient;the smaller the aperture,the greater is this coefficient.The thickness of the resonance plate has the most significant influence on the sound insulation and resonance frequency;the greater the thickness,the wider the frequency domain in which sound insulation is obtained.In addition,the effect of filling the structural cavity with porous foam ceramics has been studied,and it has been found that the porosity and thickness of the porous material have a significant effect on the sound absorption coefficient and sound insulation,while the pore size exhibits a limited influence.

Improving the Sound Absorption Properties of Flexible Polyurethane (PU) Foam using Nanofibers and Nanoparticles

Polyurethane foam as the most well-known absorbent materials has a suitable absorption coefficient only within a limited frequency range.The aim of this study was to improve the sound absorption coefficient of flexible polyurethane(PU)foam within the range of various frequencies using clay nanoparticles,polyacrylonitrile nanofibers,and polyvinylidene fluoride nanofibers.The response surface method was used to determine the effect of addition of nanofibers of PAN and PVDF,addition of clay nanoparticles,absorbent thickness,and air gap on the sound absorption coefficient of flexible polyurethane foam(PU)across different frequency ranges.The absorption coefficient of the samples was measured using Impedance Tubes device.Nano clay at low thicknesses as well as polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers at higher thicknesses had a greater positive effect on absorption coefficient.The mean sound absorption coefficient in the composite with the highest absorption coefficient at middle and high frequencies was 0.798 and 0.75,respectively.In comparison with pure polyurethane foam with the same thickness and air gap,these values were 2.22 times at the middle frequencies and 1.47 times at high frequencies,respectively.Surface porosity rose with increasing nano clay,but decreased with increasing polyacrylonitrile nanofibers and polyvinyl fluoride nanofibers.The results indicated that the absorption coefficient was elevated with increasing the thickness and air gap.This study suggests that the use of a combination of nanoparticles and nanofibers can enhance the acoustic properties of flexible polyurethane foam.

Sound absorption characteristic of micro-helix metamaterial by 3D printing

We present the design of micro-helix metamaterial supporting high sound absorption characteristic by 3D printing. The sample structure which is fabricated out of polylactide （PLA） material, many micro-helix are arranged by periodic arrays on XY plane. Experiment measurement results show that different geometrical dimensions of helix vestibule and cavity depth have a great effect on sound absorption coefficient. Physical mechanism depends on the friction and viscosity between the air and the helix vestibule. This work shows great potential of micro-structure metamaterial in noise control applications require light weight and large rigid of sound absorption.

The vibroacoustic response and sound absorption performance of multilayer, microperforated rib-stiffened plates

The vibroacoustic response and sound absorption performance of a structure composed of multilayer plates and one rigid back wall are theoretically analyzed. In this structure, all plates are two-dimensional, microperforated, and periodically rib-stiffened. To investigate such a structural system, semianalytical models of one-layer and multilayer plate structures considering the vibration effects are first developed. Then approaches of the space harmonic method and Fourier transforms are applied to a one-layer plate, and finally the cascade connection method is utilized for a multilayer plate structure. Based on fundamental acoustic formulas, the vibroacoustic responses of microperforated stiffened plates are expressed as functions of a series of harmonic amplitudes of plate displacement, which are then solved by employing the numerical truncation method. Applying the inverse Fourier transform, wave propagation, and linear addition properties, the equations of the sound pressures and absorption coefficients for the one-layer and multilayer stiffened plates in physical space are finally derived. Using numerical examples, the effects of the most important physical parameters-for example, the perforation ratio of the plate, sound incident angles, and periodical rib spacing-on sound absorption performance are examined. Numerical results indicate that the sound absorption performance of the studied structure is effectively enhanced by the flexural vibration of the plate in water. Finally, the proposed approaches are validated by comparing the results of stiffened plates of the present work with solutions from previous studies.

Experimental investigation of sound absorption in a composite absorber

A composite absorber made of a polyurethane sponge and multi-layer micro-perforated plates is pre-sented in this study.Results from an acoustic impedance tube test show that the polyurethane sponge can exhibits higher low-frequency sound absorption in front of the micro-perforated plate,while sound absorption at medium and high-frequencies remains low.The physical mechanism behind this is that the micro-perforated plate increases the denpth cavity.If the polyurethane sponge is placed behind the micro-perforated plate,the amplitude of the original absorption peak will remain constant,but the ab-sorption peaks will shift to lower frequencies.The reason for this phenomenon is that porous materials with low flow resistance can be approximately equivalent to fluid,which not only does not affect the res-onance absorption coefficient of micro-perforated plate,but also makes the peaks move to low frequency.This study has the potential applications in the sound absorption design of composite structure.

Improving the Cellular Characteristics of Aluminum Foam for Maximum Sound Absorption Coefficient Using Genetic Algorithm

Fabricating of metal foams with desired morphological parameters including pore size,porosity and pore opening is possible now using sintering technology.Thus,if it is possible to determine the morphology of metal foam to absorb sound at a given frequency,and then fabricate it through sintering,it is expected to have optimized metal foams for the best sound absorption.Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient.In this study,the Lu model was used to optimize the morphological parameters of aluminum metal foam for the best sound absorption coefficient.For this purpose,the Lu model was numerically solved using written codes in MATLAB software.After validating the proposed codes with benchmark data,the genetic algorithm(GA)was applied to optimize the affecting morphological parameters on the sound absorption coefficient.The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz.The optimized parameters ranged from 50%to 95%for porosity,0.1 mm to 4.5 mm for pore size,and 0.07 mm to 0.6 mm for pore opening size.The result of this study was applied to fabricate the desired aluminum metal foams for the best sound absorption.The novel approach applied in this study,is expected to be successfully applied in for best sound absorption in desired frequencies.

Effect of ocean environmental factors on sound absorption by boric acid relaxation in sea water

By using the expressions for the maximum absorption per wavelength (αλ),and the relaxation frequency fr of the boric acid relaxation derived previously by the author and employing the related oceanographic literatures, the effects of pressure, temperature, pH and salinity on (αλ)r and ∫r of the boric acid relaxation in sea water have been estimated. Results show that ( αλ), not only increases with pH but also increases approximately linearly with pressure and temperature, and is nearly proportional to the 1. 35 power of salinity. However, pressure, pH and salinity have negligible effect on ∫r; therefore, ∫r, can be approximately expressed as a function of temperature only. Comparisons of the predicted with the measured ( αλ)r and ∫r in different ocean areas are given.

Research Progress of Underwater Soundabsorbing Material

This article provides an overview of underwater sound-absorbing materials mainly applied with polyurethane matrix.It mainly elaborates on the underwater sound mecha-nism,commonly used underwater sound-absorbing materials and structures,as well as new underwater sound-absorbing material structures derived from local resonance pho-nonic crystals,such as phononic crystals,local resonance phonon wood piles,and meta-material sound-absorbing structures.This provides a broader development space and direction for the future development of underwater sound-absorbing materials.

INVESTIGATION ON SOUND ABSORPTION PROPERTIES OF KAPOK FIBERS

Sound absorption properties of natural kapok fibers have been investigated. Kapok fibrous assemblies with different bulk density, thickness, fiber length and orientation were manufactured, and their acoustical performances were evaluated by using an impedance tube instrument. Results show that the kapok fiber has excellent acoustical damping performance due to its natural hollow structure, and the sound absorption coefficients of kapok fibrous assemblies are significantly affected by the bulk density, thickness and arrangement of kapok fibers but less dependent on the fiber length. Compared with assemblies of commercial glass wool and degreasing cotton fibers, the kapok fiber assemblies with the same thickness but much smaller bulk density may have the similar sound absorption coefficients. Theoretical modelling of the acoustical damping performance of kapok fibers shows a good agreement with the experimental data. All the results demonstrate that kapok fiber is a promising light and environment-friendly sound absorption material.

Decoupling multimode vibrational relaxations in multi-component gas mixtures: Analysis of sound relaxational absorption spectra

Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.

SOUND ABSORPTION BEHAVIOR OF ELECTROSPUN POLYACRYLONITRILE NANOFIBROUS MEMBRANES

The acoustical damping property of electrospun polyacrylonitrile （PAN） nanofibrous membranes with different thicknesses and porosities was investigated. The sound absorption coefficients were measured using the impedance tube instrument based on ISO10534-2：1998（E）. Results indicate that the first resonance absorption frequency of nanofibrous membranes shifts to the lower frequency with the increase of the back cavity or the thickness of membranes. Moreover, the sound absorption performance of the perforated pane/ can be greatly improved by combination with a thin layer of PAN nanofibrous membrane. Traditional acoustical damping materials （foam, fiber） coated with nanofibrous membranes have better acoustical performance in the low and medium frequency range than that of acoustical materials alone. All of the results demonstrate the PAN nanofibrous membrane is a suitable candidate for noise reduction.

Multifunctional aramid nanofibers reinforced RGO aerogels integrated with high-efciency microwave absorption, sound absorption and heat insulation performance

Although lightweight and three-dimensional(3 D) graphene aerogels are highly desirable for microwave absorption(MA) due to their high porosity,specific surface area,and 3 D conductive network,it still remains a large challenge to construct a multifunctional application framework to quickly adapt to the complex practical environment,making it to be efficiently applied in a variety of complex situation.Herein,multifunctional aramid nanofibers(ANFs) reinforced reduced graphene oxide aerogels(RGO@ANF) have been achieved by in-situ gel reaction,freeze-drying,and thermal annealing processes.The introduced ANFs in RGO aerogels can prevent the graphene sheets from over-stacking and enhance the connectivity of cell walls,thus leading to excellent compression resistance,MA,sound absorption,and thermal insulation performance.Under 70% strain,the maximum compressive stress of RGO@ANF aerogel reaches78.8 kPa,and reversible compressibility with reliable resistance to fatigue for 100 compressive cycles at20% strain.Further,the RGO@ANF aerogel exhibit a minimum reflection loss(RL_(min)) of-56.5 dB and a maximum effective absorption bandwidth(EAB) of 7.0 GHz at a thickness of 2.8 mm,basically covering the X and Ku bands.Moreover,the hybrid aerogel exhibited excellent sound absorption with an average absorption coefficient> 0.56 at 2-6 kHz and good thermal insulation performance with low thermal conductivity of about 49.18 mW m-1K-1.The integrated graphene aerogels with such multifunctional performances hold a great promise for applications such as MA,sound absorption,and heat insulation.

Enhancement of low-frequency sound absorption of microperforated panels by adding a mechanical impedance

In order to solve the bad low frequency sound absorption of the Micro-Perforated panel （MPP） absorber, mechanical impedance was introduced in the back of the MPP absorber to form a composite structure. According to the same particle vibration velocity on both sides of a plate, the mechanical impedance plate transfer matrix could be obtained. The units of the mechanical impedance, cavity and MPP were connected in series with the use of the transfer matrix method, thus creating the composite structure＇s theoretical calculation model. The qual- ity factor affecting absorption bandwidth was analyzed. Bandwidth is inversely proportional to the mechanical impedance plate mass. During the experiments, when at close to 400 Hz, the composite structure reached an absorption peak with a coefficient of above 0.8. Experimen- tal results concurred with theoretical calculations. Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism. Through this, the performance of low frequency sound absorption can be improved without increasing the thickness of the structure. The frequency band can be broadened by reducing the mechanical impedance plate mass and controlling its boundary-damping coefficient.

Light Electrospun Polyvinylpyrrolidone Blanket for Low Frequencies Sound Absorption

Light polymeric soundproofing materials （density = 63 kg/m3） of interest for the transportation industry were fabricated through electrospinning. Blankets of electrospun polyvinylpyrrolidone （average fiber diameter = （1.6 ± 0.5） or （2.8 ± 0.5） μm） were obtained by stacking disks of electrospun mats. The sound absorption coefficients were measured using the impedance tube instrument based on ASTM E1050 and ISO 10534-2. For a given set of disks （from a minimum of 6） the sound absorption coefficient changed with the frequency （in the range 200-1600 Hz） following a bell shape curve with a maximum （where the coefficient is greater than 0.9） that shifts to lower frequencies at higher piled disks number and greater fiber diameter. This work showed that electrospinning produced sound absorbers with reduced thickness （2-3 cm） and excellent sound-absorption properties in the low and medium frequency range.

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.

Sound absorption characteristics of microperforated absorbers for random incidence

Based on previous work on 'Statistical absorption coefficient of microperforated absorbers', in which it was shown that theoretical results agree well with experiments on the absorption characteristics of microperforated absorbers (MPA) for random incidence. Further work was carried out in this investigation of the statistical absorption coefficients of MPA in random fields by computation, in order to find the best. structure of MPA. It is established that ordinarily the absorption curves of MPA for random incidence and that for normal incidence are quite alike, only that the absorption coefficients are more or less reduced and the whole curve is shifted to higher frequencies without any change of shape. But when the perforate constant k = d ωρ0/4η where d is the diameters of perforations in mm and f0, the absorbers resonance frequency is reduced below 2, say, secondary absorption bands start to play more important role. Pretty soon, they merge with the main absorption band and form a long tail of the latter,extending the absorption far into high frequencies, raising the resulting absorption band to three, four or more octaves. The behavior of the secondary absorption bands is discussed.

Grating‐like anechoic layer for broadband underwater sound absorption

To address the challenging task of effective sound absorption in the low and broad frequency band for underwater structures,we propose a novel grating‐like anechoic layer by filling rubber blocks and an air backing layer into metallic grating.The metallic gratings are incorporated into the anechoic layer as a skeleton for enhanced viscoelastic dissipation by promoting shear deformation between rubber and metal plates.The introduction of an air backing layer releases the bottom constraint of the rubber,thus intensifying its deformation under acoustic excitation.Based on the homogenization method and the transfer matrix method,a theoretical model is developed to evaluate the sound absorption performance of the proposed anechoic layer,which is validated against finite element simulation results.It is demonstrated that a sound absorption coefficient of the grating‐like anechoic layer of 0.8 can be achieved in the frequency range of 1294-10000 Hz.Given the importance of sound absorption at varying frequencies,the weighted average method is subsequently used to comprehensively evaluate the performance of the anechoic layer.Then,with structural density taken into consideration,an integrated index is proposed to further evaluate the acoustic properties of the proposed anechoic layer.Finally,the backing conditions and the boundary conditions of finite‐size structures are discussed.The results provide helpful theoretical guidance for designing novel acoustic metamaterials with broadband low‐frequency underwater sound absorption.

Studies on the sound absorption and transmission loss performances of wood-based, natural and wastematerials

The sound absorption and sound transmission loss performances of the natural woods,hard and soft processed woods with attachment of the various natural orwastematerials were investigated in the present study using impedance tube with American Society for Testing Material(ASTM)standards.The sound absorption performances of all natural and all hard processed woods were very poor.It was found that filter mat made by the coconut fibre was the best material for sound absorption improvement of the hard processed woods.The sound absorption performance of the soft processed wood(cork)was better than all natural and all hard processed woods.Among all tested woods,it was found that the cork with attached tea bag made by corn fibre is the best selection for sound absorption application.The transmission loss performances of all natural woods were good.The effects of various materials on the transmission loss performances of all hard processed woods were not very significant.For cork with and without attachment of various materials,their transmission loss performances were not as good as the hard processed woods.Among all tested woods,it was found that Pterocarpus soyauxii and Quercus spp.(natural woods)are the best woods to be used in those applications when prevention of sound transmission is needed.It is recommended that cork is the best wood to be used in those applications where sound absorption and prevention of sound transmission are needed at the same time due to its good sound absorption performance while its ability on prevention of the sound transmission is also acceptable.