Absorption Of Sound Waves Research Articles

Anisotropic cellulose-based phase change aerogels for acoustic-thermal energy conversion and management

Porous materials are usually used as sound-absorbing materials to alleviate noise pollution problems. However, the heat energy conversed from the acoustic energy is wasteful. Herein, anisotropic cellulose-based phase change aerogels (MXene/CNF-C/PEG aerogels) are fabricated by facile directional freeze casting method with anisotropic porous structure, efficient sound wave absorption, acoustic-thermal conversion and thermal management capability. MXene/CNF-C/PEG aerogels with shape stability are formed by hydrogen bonding forces between carboxylated cellulose nanofibers (CNF-C) and PEG without chemical crosslinking. The addition of MXene not only increases thermal conductive performance to 150 % but also enhances acoustic-thermal conversion ability effectively. Moreover, the directional porous MXene/CNF-C/PEG aerogels (DMCPs) possess high energy storage density (143.0 J/g) and acoustic-thermal conversion performance, which open up broad application prospect in the field of acoustic to heat energy conversion and storage.

Enhancing Sound Transmission Loss in Hybrid Mufflers with Change in Pipe Perforation and Using Absorptive Material

It is well known that baffled exhaust mufflers enhance sound transmission loss while lowering noise emissions. Sound transmission loss can be further reduced by adding sound-absorbing material inside the silencer. It has been demonstrated that carefully placed baffles in exhaust silencer systems improve acoustic performance by successfully lowering noise emissions. Sound waves are redirected and disrupted by baffles, which lessens the transmission of undesired noise and creates a more controlled and tranquil acoustic environment. The incorporation of sound-absorbing materials into mufflers is a significant development in noise control technology. Specialized materials are added to the muffler to improve sound wave absorption and drastically reduce noise emissions. This novel method not only enhances acoustic performance but also improves a variety of applications—from industrial gear to automobile exhaust systems—making them quieter and more enjoyable to use. A silencer was constructed for this research project using the finite volume method. The design's efficacy was demonstrated through experimental validation. The research project then used the finite volume technique to produce a silencer with the same dimensions. It then adjusted the design based on different flow percentages, adding a baffle and making pipe perforations, until the optimal silencer design was found. Additionally, this approach provides an optimal design and indicates which sound-absorbing material has the largest sound transmission loss.

Шумоизолирующий кожух с резонаторными элементами

Constant exposure to industrial noise has a negative impact on the human body. That is why increased attention is paid to the fight against noise, the rationing of industrial noise and vibrations was adopted. One of the effective methods to reduce the noise emitted by the operating equipment is the use of noise-insulating casings. The casing, as a rule, contains an outer skin made of steel sheet, a sound-absorbing lining of the inner skin, a perforated lining of a sound-absorbing coating. A typical octave spectrum of radiation sound pressure levels near the machine has a maximum near the frequency of 500 Hz, and the highest casing efficiency (insertion loss) is achieved in the frequency range of 1000–4000 Hz. The purpose of the study presented in the article is to improve the acoustic properties of the noise-insulating casing in the medium and low-frequency sound spectrum. To accomplish this task, the author proposes integrating resonator elements, in particular, Helmholtz resonators, into the structure of the noise-insulating casing. The natural resonant frequencies of Helmholtz acoustic resonators are determined considering their necessary frequency tuning, which ensures effective suppression of sound radiation at discrete values of the operating dominant frequencies of operating equipment. To reduce the excitation of structural vibrations and sound, as well as additional sound insulation, the frame walls and casing covers are damped on the outside and inside with a layer of vibration-damping material. Significant absorption of sound waves generated by operating equipment is ensured by lining the casing walls with effective sound-absorbing panels made of porous material, lined, in turn, with an external protective sound-transparent layer. The design of a noise-insulating casing with resonator elements presented in the study has high acoustic properties in a wide frequency range. Helmholtz resonators built into the casing structure provide sound absorption in 1/3 octave frequency bands centered at 400 and 500 Hz, characterized by a resonant amplification of the sound emitted by the equipment discussed in the article.

Sound Wave Absorption Coefficient and Sound Velocity in Thermally Modified Wood

The present work analyses the absorption coefficient of sound waves and the speed of sound propagation in thermally modified wood. The high resistance to weathering, fungi, and better dimensional stability, and therefore the broad physical properties of this material, are well known. However, the literature lacks numerous analyses of its acoustic characteristics. During the study, high-density species, such as oak, red oak, and beech were used, in contrast to pine. Pine wood during this test was characterised by a most rapid increase in the sound absorption coefficient value, in the range of 1000–6300 Hz, and reached the highest value from all wood species. Among all species, the highest value of the examined parameter was obtained for beech wood and pine wood, which were 0.213 (at frequency 3 kHz) and 0.183 (at 6.3 kHz), respectively. The sound velocity decreased for all species only in the tangential direction.

Modelling underwater noise mitigation of a bubble curtain using a coupled-oscillator model

Bubbles can inhibit underwater sound transmission, owing to density and acoustic-impedance mismatches and associated reflection and absorption of sound waves, and also scattering due to bubble-acoustic resonances. Thus, bubble curtains have been used to reduce underwater noise propagation. For the present study, a discrete bubble model (DBM) utilising self-consistent coupled-oscillator theory was developed to model noise mitigation by bubble curtains. The DBM is inherently able to handle polydisperse-sized and anisotropically-distributed bubbles. The DBM was shown to accurately predict the bubble collective resonance frequencies of 1D line, 2D planar and 3D complex bubble cloud configurations. Subsequently, the model demonstrated that the collective resonance frequency decreases as the inter-bubble spacing was reduced in 2D planar bubble screens and 3D cylindrical bubble curtains. Modal analysis indicated that the fundamental mode in both configurations dominated the vibration of bubble clouds when subjected to an external acoustic source. The broadband acoustic pulse levels were able to be reduced by approximately 17 dB using realistic cylindrical bubble curtain configurations with a diameter of 5 m and two different gas volume fraction values of 1% and 2%. Variations in the sizes of bubbles within a curtain were shown to have a significant impact on curtain performance, whereas variations in inter-bubble spacing had no significant impact, implying that bubble-curtain operators should focus on controlling the size of the bubbles.

A thin-film acoustic metamaterial absorber with tunable sound absorption characteristics.

A thin-film absorber with tunable acoustic properties over a wideband is designed based on the acoustic metamaterial theory. The thin-film acoustic metamaterial absorber (TFAMA) consists of a frame made of piezoelectric material and several flexible films with attached mass blocks (mass-spring vibration system). Based on the vibration mechanism of the mass-spring vibration system, a cellular model of local resonance form is established, and the material properties of negative effective mass are discussed. Combined with the vibration modal analysis of the coupling of mass block, elastic film, and piezoelectric material, the acoustic characteristics of the TFAMA under alternating voltage excitation are studied by finite element and experimental methods. The simulation and experimental results show that the sound wave can be well absorbed when it is incident on TFAMA to cause the membrane-cavity coupling resonance. By applying an alternating voltage to the TFAMA to excite the mass-spring vibration system to generate local resonance, the absorption of sound waves can be further enhanced in a relatively wide band near the excitation frequency. In view of the convenience of voltage parameter adjustment, the sound absorption band can be flexibly tuned in a wide range, including low frequency.

Characterization of Sound Absorption Coefficient and Acoustic Impedance of Palm Frond Fiber Composites with Pine Resin on Various Composition Variations

This research aims to investigate the ability of sound absorption coefficient and the acoustic impedance of Palm Frond Fiber Composites using the one-microphone impedance tube method. We used Palm Frond Fibers as a filler and pine resin as an alternative adhesive of composite with a volume fraction of 50%: 50%, 60%: 40%, 70%: 30%, 80%: 20%, and 90%: 10%. The sound absorption coefficient and acoustic impedance of composites were studied at 500, 1000 Hz, 1500 Hz, 2000 Hz, and 2500 Hz frequency. The results showed that the highest sound absorption coefficient was found in 1500 Hz frequency and using volume fraction 70%:10%. The highest acoustic impedance response was found in composite with a fiber composition of 90% and at the test frequency with a range of 500 Hz -1500 Hz. The composition of the adhesive and fiber greatly affects the impedance value because it was related to the formation of pores in the composite. Based on ISO standard 11654:1997, the value of the sound absorption of sound waves was 0.15, and Palm Frond Fiber had a value above, so it had the potential used as sound absorption material.

Low-frequency sound-absorbing metasurface constructed by a membrane-covered and coiled Helmholtz resonator

Achieving broadband absorption of sound waves below 500 Hz with materials of sub-wavelength thickness is significant but still a great challenge in academia and industries. Here, we present and theoretically analyze an airtight sound-absorbing metasurface constructed by a membrane-covered and coiled Helmholtz resonator. It is discovered that the metasurface possesses a near-perfect absorption with a working wavelength approximately 33.6 times greater than the total thickness, which stems from synthetic modulation on acoustic reactance brought by the membrane, air gap formed behind the membrane, and a coiled channel. Furthermore, on-demand broadband absorption below 500 Hz is achieved by parallel assemblies consisting of four subunits. An excellent agreement between measurements and predictions confirms the validity of the proposed structures. The airtight construction also broadens its application scenarios compared to the common perforated absorbers with open pores directly exposed to external environments. Our design provides a new structure paradigm for low-frequency sound absorption.

Sound absorption in glasses

The paper presents a description of the sound wave absorption in glasses, from the lowest temperatures up to the glass transition, in terms of three compatible phenomenological models. Resonant tunneling, the rise of the relaxational tunneling to the tunneling plateau and the crossover to classical relaxation are universal features of glasses and are well described by the tunneling model and its extension to include soft vibrations and low barrier relaxations, the soft potential model. Its further extension to non-universal features at higher temperatures is the very flexible Gilroy-Phillips model, which allows to determine the barrier density of the energy landscape of the specific glass from the frequency and temperature dependence of the sound wave absorption in the classical relaxation domain. To apply it properly at elevated temperatures, one needs its formulation in terms of the shear compliance. As one approaches the glass transition, universality sets in again with an exponential rise of the barrier density reflecting the frozen fast Kohlrausch t β -tail (in time t , with β close to 1/2) of the viscous flow at the glass temperature. The validity of the scheme is checked for literature data of several glasses and polymers with and without secondary relaxation peaks. The frozen Kohlrausch tail of the mechanical relaxation shows no indication of the strongly temperature-dependent barrier density observed in dielectric data of molecular glasses with hydrogen bonds. Instead, the mechanical relaxation data indicate an energy landscape describable with a frozen temperature-independent barrier density for any glass.

Объемная вязкость в жидкостях и в жидких дисперсных системах

The paper provides a brief review of studies of the bulk viscosity of liquids and liquid dispersed systems. Obtaining experimental data on the viscosity of liquid dispersed (colloidal) systems is complicated by a number of factors: the difficulty of creating monodisperse systems, various methodological problems of accurately measuring the size of particles, their concentration, degree of homogeneity, and distribution. And also the difficulty lies in the fact that with an increase in the concentration of particles, a liquid dispersed system from a Newtonian liquid becomes non-Newtonian. The absorption of acoustic waves in a liquid is associated with both shear and bulk viscosity. It is shown that in most cases the value of bulk viscosity is much higher than the value of shear viscosity, and their ratio changes with increasing temperature. The data obtained on the basis of the Stokes model of absorption of sound waves are considered.

Study of an insulating hemp-based bio-material: mechanical, thermal and acoustic properties

Currently there is a need to develop more sustainable and renewable materials compromised with the environment. From these needs, hemp stalk has great potential because it is mostly a waste material. Moreover, hemp shives are a lightweight material with a high insulating property. This study aims to increase the knowledge in a material made solely from stalk and ECF (elementary chlorine free) bleached eucalyptus kraft pulp and a second 100% recycled material where the kraft pulp is replaced by recycled cardboard fiber, also a vegetable coating is added to protect against moisture. The hemp/fiber ratio influence is studied. Samples are evaluated in terms of mechanical behaviour (compression and shear), thermal and acoustic insulation. To study the thermal insulation, a testing camera is used where the heat transfer through the material is measured in order to study the thermal resistance. A Kundt tube is used in the acoustic insulation study to calculate the absorption of sound waves in a range from 0 to 6500 Hz. The results show that by increasing the percentage of hemp, the mechanical properties increase (compression and shear). Also, the eucalyptus pulp acts as a binder between the shives; nevertheless, if there is not enough, the material is not stable. Therefore, a maximum of 70 wt.% of hemp is recommended. In the case of thermal insulation, better thermal resistance is obtained in the case of 60 wt.% of hemp, while in acoustic insulation a higher percentage of hemp have a high performance, reaching attenuation values greater than 0.8 for frequencies greater than 1000Hz. The carboard sample improves the shear and acoustic insulation performance. The coating improves the thermal resistance but worsens the acoustic insulation.

Dynamical spectral structure of density fluctuation near the QCD critical point

The expression for the dynamical spectral structure of the density fluctuation near the QCD critical point has been derived using linear response theory within the purview of Israel–Stewart relativistic viscous hydrodynamics. The change in the spectral structure of the system as it approaches the critical point has been studied. The effects of the critical point have been introduced in the system through a realistic equation of state and the scaling behaviour of various transport coefficients and thermodynamic response functions. We have found that the Rayleigh and Brillouin peaks are distinctly visible when the system is away from the critical point but the peaks tend to merge near the critical point. The sensitivity of the structure of the spectral function on wave vector (k) of the sound wave has been demonstrated. It has been shown that the Brillouin peaks get merged with the Rayleigh peak because of the absorption of sound waves in the vicinity of the critical point.

Phase change materials with Fe3O4/GO three-dimensional network structure for acoustic-thermal energy conversion and management

Sonic energy can be converted into thermal energy by ultrasonic thermal effect, which has significant application value in the fields of denoising and minimally invasive thermotherapy. Acoustic thermal conversion and thermal energy management capacities need to effectively improved during the process of acoustic-thermal utilization. Herein, we report novel PEG/Fe3O4-GO form-stable phase change materials (PCMs) with efficient sound wave absorption, acoustic-thermal conversion and thermal management capability. The PCMs are prepared by in-situ encapsulating polyethylene glycol (PEG) into graphene oxide (GO) network functionalized with Fe3O4 nanoparticles. The unique construction of three-dimensional (3D) network structure not only improve thermal conductive performance but also enhance sound absorption ability effectively. Moreover, the acoustic-thermal conversion is further enhanced through the vibration heat production of Fe3O4 nanoparticles. As a result, the form-stable composites exhibit superior energy storage density (173.7 J/g) and acoustic-thermal conversion performance. Thereby opening up a broad application prospect in the field of acoustic to heat energy conversion and storage.

Nonplanar metasurface for perfect absorption of sound waves.

We propose a sound-absorbing nonplanar metasurface by considering locally different incidence angles along the metasurface. Perfect sound absorption is realized with the aid of hybrid resonance between two different subwavelength Helmhwoltz resonators comprising a unit cell. We theoretically investigate the effect of incidence angles on the sound absorption of the unit cells, and present a design method of the nonplanar metasurface that achieves perfect absorption by considering locally different incidence angles along the metasurface. The perfect absorption of plane sound waves on nonplanar surfaces is numerically demonstrated at the target frequency of 1 kHz. The numerical results show that at least 99.8% of the incident wave energy is absorbed by the designed metasurfaces with a thickness of λ/24. A nonplanar metasurface is fabricated via three-dimensional printing, and perfect sound absorption is experimentally validated at the target frequency of 1 kHz. Furthermore, we design nonplanar metasurfaces that can perfectly absorb cylindrical sound waves when a line source is located near the metasurface. While previous sound-absorbing metasurfaces focused only on planar surfaces, the proposed method achieves perfect sound absorption on nonplanar surfaces, expanding the range of practical applications in various industrial areas.

ВЛИЯНИЕ ПОРИСТОЙ СТРУКТУРЫ НА ЗВУКОПОГЛОЩЕНИЕ ЯЧЕИСТОГО БЕТОНА

the compositions of gas and foam concrete with improved acoustic characteristics were developed. The optimal form of porosity, which contributes to the absorption of sound waves, both in the range of audible frequencies and at infrasonic and ultrasonic frequencies, is revealed. The mathematical model for designing sound-absorbing concrete was improved, taking into account both the porosity of the composite and the influence of the porous aggregate. The laws of synthesis of aerated concrete and foam concrete are established, which consist in optimizing the processes of structure formation due to the use of a polymineral cement-ash binder and blowing agent. The composition of the composite intensifies the process of hydration of the system, which leads to the synthesis of a polymineral heterodisperse matrix with an open porosity of more than 60%. Peculiarities of the influence of the “Portland cement – aluminosilicate – complex of modifiers” system on the rheology of the concrete mixture was identified, which can significantly reduce shear stress and create easily formed cellular concrete mixtures. The increased activity and granulometry of aluminosilicates predetermine an increase in the number of contacts and mechanical adhesion between particles during compaction, strengthening the frame of inter-pore septa. The mechanism of the influence of the composition of the concrete mixture on the microstructure of the composite is established. The presence of refined aluminosilicates and a complex of additives in the system along with cement contribute to the synthesis of the matrix with open porosity, thereby increasing the sound absorption coefficient.

Investigation on energy dissipation by polarization switching in ferroelectric materials and the feasibility of its application in sound wave absorption

In the current paper, energy dissipation via stress-induced polarization switching in ferroelectric material is investigated, and the feasibility of its application in sound wave absorption is analysed. For the system design and analysis, a phenomenological model based on the modified Landau phase transition theory is constructed to describe the polarization switching. A simple and robust energy dissipation prototype is introduced. The hysteretic dynamics associated with the polarization switching process and the energy dissipation process are investigated. The dependence of the energy dissipation on the bias voltage, frequency, and resistance is analysed in detail. The energy dissipation density in one cycle is calculated. It is shown that the resistance has a strong influence on the energy dissipation. Meanwhile, a better energy dissipation effect could be obtained by setting an appropriate resistance for the low-frequency excitation. The feasibility of using ferroelectric materials for low-frequency sound wave absorption is validated. For a specific acoustic energy dissipation device, corresponding design and analysis will be discussed in our future papers.

Sound absorption performance of a filled honeycomb composite structure

A new composite structure was formed by filling Nomex honeycomb with polyester fibre to achieve the goal of improving its acoustic characteristics. By using the impedance tube method, the sound absorption coefficient (SAC) of porous materials was determined. Moreover, the effects of different specifications of honeycomb, porosities of fibre, and amount of filler on SAC were studied to achieve the experimental objective. The experimental results demonstrate that the increase of porosity of filler can improve the SAC of the test sample. Honeycombs with different specifications slightly influence the SAC of the sample and the influencing factor may be additional absorption of sound waves caused by contact between materials. Different filling amounts can change the SAC of the sample, while SAC does not improve significantly in the high-frequency range. Simulation results using Virtual Lab. show that porosity of the materials affects the sound absorption performance thereof. The data and conclusions obtained in experiments and simulation provide support for the application of honeycomb sandwich panels in acoustics and noise reduction.

Modeling of acoustic porous material absorber using rigid multiple micro-ducts network: Validation of the proposed model

Porous materials present many important characteristics for the field of acoustics like thermal insulation, acoustic absorption, impact insulation and lightweight. There are many situations where one can find applications, such as aeronautics, automotive industries, heat and air conditioning systems, buildings, industry in general and others. Nowadays, with advances in the material fabrication process, it's possible to create complex structures according to the final objective. In this study, the greater interest is to increase sound wave absorption for industrial or residential applications. For a complete understanding of the needed characteristics to have a good absorber, it is recommended to model the structure through geometric pore reconstruction. This is a better way to later define which direction to take in order to increase the absorption curve, as well as which modifications and geometric restrictions must be performed to manufacture the best material for a given application. Simple macroscopic or empiric analytical models can be used to describe the visco-thermal dissipation inside the material. However, this approach does not present a clear link between micro and macro properties. This study proposes the reconstruction of cellular porous media using microscopic technique images. The proposed model basically is a 2D duct network made of simple uni-dimensional acoustical cylinders or pores. The theory based on acoustic transfer matrix method and mobility matrix model has been merged with analytical visco-thermal dissipation to implement the model proposed. Two cellular materials have been experimentally validated against the surface impedance and absorption for normal incidence: melamine foam and the porous aluminum. Valid agreements have been found between the experimental and numerical data. Future experiments will investigate geometry optimization methods to increase the absorption curve in frequency bands of interest.

Honeycomb locally resonant absorbing acoustic metamaterials with stop band behavior

This study presents the design of a locally resonant absorbing metamaterial in the form of cubes and rectangular cubes, formed from square and honeycomb shaped unit cells. In this context, we fabricated a box consisting of acoustic metamaterial panels to validate our numerical simulation model. Then, we developed simulation models of acoustic metamaterials with square and honeycomb unit cells, forming cubic and rectangular cube sound barriers. Our purpose was to verify the operating frequency range of the designed metamaterial and then, compare the behavior of the different acoustic metamaterial structures in the specified frequency range. The acoustic metamaterials proved to be significantly effective in sound wave absorption providing transmission losses of up to 17.5 dB, more or less similarly in the three different structures, due to the identical resonators used in all of the structures, despite difference in unit cell shapes, number of resonators in the unit cell, and geometry of the barrier structure (cube or rectangular cube). These perforated metamaterial structures were then, tested in a waveguide consisting of panels of locally resonating metamaterials. Simulation results indicated that significant stop band behavior appeared for both square and honeycomb structures in the frequency of 750–1200 Hz, with a transmission loss of up to 60 dB. A clear comparison with a regular plate sound insulator tuned to the same resonance frequency is made, and the bandwidth and transmission loss is compared under the constraints of same occupied space and same material type. According to the procedure described in this paper, it is possible to design stop bands with excellent performance in a certain targeted frequency range.

Chemical treatment of wood fibers to enhance the sound absorption coefficient of flexible polyurethane composite foams

Polyurethane foams are commonly used as sound absorption materials in the automobile industry because their well-defined structure allows for effective absorption of sound waves through air friction and the structural vibration of cell walls. In this study, chemically treated wood fibers were incorporated into the polyurethane foams to improve their sound absorption coefficient by enhancing the compatibility between the wood fibers and the polyurethane matrix. The open porosity of the composite foams was strongly dependent on the chemical treatments of wood fibers as well as the wood fiber contents in the composites, and it was related to the air-flow resistivity and tortuosity of the foam materials. Model calculations revealed that high air-flow resistivity led to a high sound absorption coefficient, which agreed well with experimental observations. Therefore, for achieving high sound absorption performance in composite foams, no more than the optimum amount of a coupling agent must be used to improve the interfacial compatibility between the wood fibers and the polyurethane matrix. The use of excessive amount of the silane coupling agent led to intramolecular agglomeration, thus negatively affecting the sound absorption behavior.