Acoustic Properties Of Materials Research Articles

An improved approach for normal-incidence sound transmission loss measurement using a four-microphone impedance tube

The main aim of this study is to introduce an improved method for determining the sound properties of acoustic materials which is more precise than the common wavefield decomposition method and simpler than the common transfer matrix method. In the first part of the article, a group of formulae for calculating sound transmission loss is represented by combining the wavefield decomposition and transfer matrix methods. Subsequently, a formula for calculating sound absorption coefficients is derived from these formulae by definition. Furthermore, the present formulae are validated by comparing the experimental results achieved with the present formulae and those results obtained by other methods recorded in published articles. Eventually, it is demonstrated that the method can accurately measure the sound insulation performance of materials and the sound absorption properties of limp and lightweight materials.

Critical Role of a Nanometer-Scale Microballoon Shell on Bulk Acoustic Properties of Doped Soft Matter.

A material's acoustic properties depend critically upon porosity. Doping a soft material with gas-filled microballoons permits a controlled variation of the porosity through a scalable fabrication process while generating well-tailored spherical cavities that are impermeable to liquids. However, evidence is lacking of how the nanometer-scale polymeric shell contributes to the overall effective material properties in the regime where the wavelength is comparable to the sample thickness. Here, we measure ultrasound transmission through a microballoon-doped soft material as a function of microballoon and impurity concentration, sample thickness, and frequency. The measured longitudinal wave speeds are an order of magnitude larger than those in similar systems where no shell is present, while the transverse wave speed is found to linearly increase with microballoon concentration, also in contrast to systems with no shell. Furthermore, we find the results are independent of the soft material's elastic moduli as well as a lesser contribution of the microballoon shell on material attenuation. The results are validated with a multiple scattering model and suggest the shell contributes significantly to the material's bulk acoustic properties despite its thickness being 4 orders of magnitude smaller than the acoustic wavelength. Our results demonstrate how a nanometer-scale interface between a gas cavity and a soft polymer can be used in the submicrometer design of acoustic materials, and are important for observations of such phenomena as strong interference effects in soft matter.

Introduction to Photonic and Phononic Crystals and Metamaterials

Introduction to Photonic and Phononic Crystals and Metamaterials, by Arthur R. McGurn, presents a study of the fundamental properties of optical and acoustic materials which have been of recent interest in nanoscience and device technology. The level of the presentations is appropriate for advanced undergraduates, beginning graduate students, and researchers not directly involved in the field. References are given to guide the reader to more advanced study in these fields. Discussions of the physics of photonic and phononic crystals focus on the transmission properties of optical and acoustic radiation arising from their diffractive interaction in these engineered materials. The frequency transmission and non-transmission bands of radiation are explained in terms of the symmetry properties of the photonic and phononic artificial crystal structures. Basic applications of these properties to a variety of their technological applications are examined. The physics of metamaterials is discussed along with their relationships to the ideas of resonance. Properties of negative index of refraction, perfect lens, and unusual optical effects the new optics of metamaterial media makes available are examined. Related effects in acoustics are also covered. Basic principles of surface acoustic and electromagnetic waves are explained. These form an introduction to the fundamental ideas of the recently developing fields of plasmonics and surface acoustics.

Equivalent model of spatial random array vibration system on sound-absorbing computing for porous material

Porous materials are currently the most widely used sound absorbing materials. Due to the complex sound absorption mechanism, there is no mature calculation method to analyze its sound absorption performance, which can not provide a theoretical support for the selection, analysis and design of porous sound absorbing materials. Establishing a simple and reasonable equivalent model is a prerequisite for the calculation of the acoustic properties of porous materials. The sound absorption mechanism of porous materials was explored, and the spatial topology of porous materials was reconstructed. According to the spatial characteristics of porous materials, a mass-spring-damped vibration system equivalent model of spatial random array is proposed and established. The boundary conditions of the porous sound absorbing material were studied to be equivalent to the load to analyze the sound absorbing performance. The impedance tube test method is used to verify the equivalent model of the spatial random array vibration system for the sound absorption calculation of porous materials. The results show that the simulation results of the acoustic equivalent model of porous materials are consistent with the experimental results. This research method provides technical support for the study of acoustic theoretical models of porous materials.

Airflow resistance measurement of fibrous materials at high temperatures for acoustical applications

For some industrial applications it is necessary to assess the acoustic properties of porous materials at high temperatures; hence, airflow resistance measurements on fibrous materials have been carried out at temperatures up to 800 °C. A comparison of a high temperature test rig and a test rig satisfying the requirements of ISO 9053-1 indicated no significant difference between the two rigs at room temperature. For measurements in the high temperature test rig at and above 600 °C there were changes in the sample thickness that could be linked to the onset of crystallisation. This meant that regression analysis had to establish relationships between the sample mass (rather than bulk density) and the specific airflow resistance (rather than airflow resistivity). Power law regression for AES, basalt wool and rock wool show that, on average, the specific airflow resistance is proportional to T0.7 (where T is the absolute temperature in Kelvin) at temperatures where there has been no reduction in sample thickness or other material change due to temperature. For fibrous materials, these results provide more evidence that the temperature-dependence is mainly determined by the air viscosity. Measurements on AES at 20 °C indicate negligible change in the specific airflow resistance when measured with flow velocities between 0.5 × 10−3 and 1.83 × 10−3 m/s but significant differences at 800 °C.

Scene-Aware Audio Rendering via Deep Acoustic Analysis.

We present a new method to capture the acoustic characteristics of real-world rooms using commodity devices, and use the captured characteristics to generate similar sounding sources with virtual models. Given the captured audio and an approximate geometric model of a real-world room, we present a novel learning-based method to estimate its acoustic material properties. Our approach is based on deep neural networks that estimate the reverberation time and equalization of the room from recorded audio. These estimates are used to compute material properties related to room reverberation using a novel material optimization objective. We use the estimated acoustic material characteristics for audio rendering using interactive geometric sound propagation and highlight the performance on many real-world scenarios. We also perform a user study to evaluate the perceptual similarity between the recorded sounds and our rendered audio.

Unraveling Phononic, Optoacoustic, and Mechanical Properties of Metals with Light-Driven Hypersound

A thorough understanding of the electron-phonon, thermo-optic, and acoustic properties of materials is of paramount importance for many applications in materials science and advanced applications adopting laser-induced sound waves. Even though metals are usually opaque to light, optical methods for materials characterization can still be developed, especially in the high-frequency regime, where phonon dynamics governs the thermal, acoustic, and even optical properties of metals. Ultrafast laser pulses incident on metals can lead to the generation of coherent phonon wave packets with frequencies in the gigahertz to terahertz range, providing a means to study the material properties in this otherwise inaccessible frequency range. While this principle has been known, the complex interplay of light and matter in both the generation and detection of such ultrafast hypersound pulses has limited its use mainly to geometrical effects. Here, we demonstrate the quantitative characterization of a range of different material properties using laser-driven hypersound. We use all-optical generation and detection of hypersound pulses to sensitively probe the bulk properties of various metals. We introduce an advanced two-dimensional numerical model that captures the generation, propagation, and detection of these hypersound waves in full detail. The combination of experiment and simulation allows us to unravel and elucidate various physical effects that appear over a wide range of different time scales. Through least-squares fitting of the data to the simulation results, we extract quantitative information about the electron-phonon, thermo-optic, and acoustic properties of metal films, establishing the ability to use light as a sensitive probe for the study of opaque materials.

A comprehensive study of mechanical and acoustic properties of selective laser melting material

In this research work, four groups of selective laser melted specimens were built from AlSi10Mg-0403 powder. Each group represents the direction with respect to the bed in which the specimens are built (X, Y, Z and 45° orientation). The mechanical properties of the specimens are characterized in terms of yield strength, ultimate tensile strength, Young’s modulus and elongation at break. In addition to that, the acoustic emission (AE) during the testing was monitored using wide-band high-accuracy piezoelectric sensors. The AE results were related to the mechanical characteristics of the specimens in terms of the acoustic parameter-based data, the peak amplitude, cumulative energy and count rate. The mechanical results show that the specimens built along the z direction have relatively lower strength and it can be attributed to the borderline porosity formed during the SLM process. The acoustic results can identify the critical points of failure under loading. The AE technique proves to be a powerful tool in characterizing the mechanical property and can unveil the concealed information which cannot be identified directly from the mechanical results.

Sound absorption performance of sustainable foam materials: Application of analytical and numerical tools for the optimization of forecasting models

Traditional models used to predict acoustic properties of poroelastic materials are usually applied to fibrous layers or polyurethane foams. However, for new materials like complex cellular foams these procedures may not be applied due to the different cell microstructure. To this aim, the sound absorbing properties of novel sustainable foam materials are investigated as a function of the nature and loading of waste powders and their effects on the microstructure and the acoustic properties. The foams are prepared from naturally occurring alginates that are in situ polymerized. The morphology and the acoustic properties of the foam-cells appear linked to the particle size distribution of the starting powder. Determination of the parameters of Johnson–Champoux–Allard acoustic model (tortuosity, viscous characteristic length, thermal characteristic length, porosity and flow resistivity) was performed using five different forecasting methods, including traditional analytical model for fibrous materials as well as inverse procedure. A new procedure for tortuosity computation of foam is proposed and validated. Transfer Matrix Method calculation of the absorption coefficient was performed and compared with the experimental data, in order to assess the validity of the model. Indirect method technique is demonstrated to be dependent on experimental measurement of thermal characteristic length.

Characterization of noise reduction capabilities of porous materials under various vacuum conditions

Noise pollution has been considered as a major challenge for the life of quality and engineering practices for environmental noise control for urban communities is of great importance. In this study, a series of experimental investigations are conducted to investigate the effects of a vacuum on the sound reduction and acoustic properties of porous materials. It is well known that sound cannot be transmitted under a full vacuum. However, a full vacuum condition cannot be realistically achieved in the construction process. Vacuum glass and related products are available in the market but these products can only extract a small degree of vacuum and can hardly withstand atmospheric pressure. Based on current research findings, a porous material with a certain degree of vacuum can achieve better noise reduction. The experimental setups are designed such that various porous materials can be tested, the desired vacuum levels can be maintained, and the ambience noise can be reduced to a sufficiently low level. Laboratory experiments are conducted to measure acoustic responses under various porous materials and vacuum levels. Sound intensities and corresponding frequencies are measured for porous materials with desired vacuum levels. The vacuum in porous materials, even at relatively low vacuum levels, has a significant effect on sound reduction. A vacuum of 10% in glass ball and polystyrene foam can lead to a noise reduction of more than 3 dB. The combination of vacuum and polystyrene foam has a more significant noise reduction effect, which can reach more than 8 dB for 30% vacuum. The research results may contribute to the comprehension of acoustic properties of porous materials under optimal vacuum levels. It is anticipated the research findings may lead to the construction of effective sound reducing products for noise attenuation, increasing insertion loss or improving sound insulation.

Accounting for seasonal and composition‐related variability in acoustic material properties in estimating copepod and krill target strength

AbstractEstimation of abundance or biomass, using acoustic techniques requires knowledge of the frequency dependent acoustic backscatter characteristics, or target strength, of organisms. Target strength of zooplankton is typically estimated from physics‐based models that involve multiple parameters, notably including the acoustic material properties (i.e., the contrasts in density and sound speed between the animal and surrounding seawater). In this work, variability in the acoustic material properties of two zooplankton species in the Gulf of Maine, the copepod (Calanus finmarchicus) and krill (Meganyctiphanes norvegica), was investigated relative to changing season as well as, for the copepod, temperature and depth. Increases in the density and sound speed contrasts of these species from fall to spring were observed. Target strength predictions based on these measurements varied between fall and spring by 2‐3 dB in krill. Measurements were also conducted on C. finmarchicus lipid extract at changing temperature and pressure. The density contrast of the extract varied negatively with temperature, while the sound speed contrast changed by more than 10 % over the temperature and pressure ranges that the organism expected to occupy. C. finmarchicus target strength predictions showed that the combined effect of temperature and pressure can be significant (more than 10 dB) due to the varying response of lipids. The large vertical migration ranges and lipid accumulation characteristics of these species (e.g., the diapause behaviour of Calanus copepods) suggest that it is necessary for seasonal and environmental variability in material properties to be taken into account to achieve reliable measurements.

The natural variability of spruce soundboards: Perceptual differences in the in the tonal quality of acoustic guitars

The wood of the spruce tree (Picea spp.) has been valued for centuries as an ideal soundboard for stringed instruments, due to its material acoustic properties. There is large variability in these properties between individual trees of the same species, and even within an individual log. It stands to reason that this variability would produce audible differences in sound quality in otherwise identical musical instruments. Further, there may be a specific combination of material properties of the soundboard that would result in optimal sound quality for a given design, as measured by expert listeners. Nine steel string guitars of the same model were produced by the Taylor Guitar Company, with strict control of all production parameters. The guitars varied only in two parameters: the density and the Young's modulus of the soundboard and bracewood. A short music sequence was used for pairwise comparisons in a double-blind listening test. The results suggest that, for this particular model (the Taylor 814ce Grand Auditorium), low density and Young's modulus of the soundboard and bracewood have a positive impact on overall preference. More generally, these results underscore the importance of integrating a given design with the physical characteristics of the component wood.

Perceptual evaluation of bracewood and soundboard wood variations on the preference of a steel-string acoustic guitar

The wood of the spruce tree (Picea spp.) has been valued for centuries as an ideal soundboard for stringed instruments due to its material acoustic properties. There is large variability in these properties between individual trees of the same species and even within an individual log. It stands to reason that this variability would produce audible differences in the sound quality of otherwise identical musical instruments. Furthermore, there may be a suite of physical characteristics of the soundboard that would result in optimal sound quality for a given design. Nine steel-string guitars of the same model were produced. The guitars varied only in two parameters: the density and Young's modulus of the soundboard and bracewood. This variability was representative of the range of wood currently produced by Pacific Rim Tonewoods. A short music sequence was used for a pairwise preference evaluation in a listening test. The results suggested that, for this particular model (the Taylor 814ce Grand Auditorium), the low density and Young's modulus of the soundboard and bracewood had a positive impact on the sound quality. More generally, these results underscore the importance of integrating a given design with the physical characteristics of the component wood.

Dispersion curves identification and traveling wave control in a weakly coupled impedance tube

Impedance tubes are commonly used for non-destructive measurement method of the acoustic properties of materials. Most physical models neglect the elastic nature of the tube resulting in a single mode propagation up to the cut-off frequency and are thus unable to accurately predict the propagation patterns in the case of liquid-filled tubes. An understating of the dispersion pattern in the latter case is crucial for the success of the acoustic properties estimation procedure. Furthermore, a model-based control can be implemented on the basis of the dispersion relation which is able to enhance the existing methods. This work presents a case study of an air-filled impedance tube. A novel, two-actuators phase-perturbations technique was developed to identify the tube dispersion curves and to compare to analytical models. The accurate identification of dispersion curves was utilized in a successful effort to control a single mode traveling wave ratio by employing a feedforward control algorithm. The success of the case study in the case of a weak acoustic coupling mechanism such as the air-filled impedance tube emphasizes the capabilities when considering a stronger acoustic coupling such as in the liquid-filled impedance tube.

Waveguide dispersion curves identification at low-frequency using two actuators and phase perturbations.

Dispersion curves of fluid-filled elastic-tubes are used for non-destructive measurement of material acoustic properties. The underlying physics leads to a singular numerical procedure when several modes or long-wavelength scenarios take part in the tube dynamics. The literature describes several methods to identify dispersion curves that require a large ratio of samples per length. Described is a method to enrich the amount of available information of an otherwise ill-posed problem, by multiple boundary phase perturbations at each excitation frequency. The method uses two actuators, one at either end of the waveguide to produce different relative phases, followed by a nonlinear model fitting procedure. Presented are a model-based derivation and experimental verification of the proposed approach on an air-filled elastic-tube. The latter shows the capability of the method to recover the dispersion curves even for very weak structural-acoustic coupling and at low frequencies. The portrayed scheme can be applied on various waveguides by using two actuators and only a single sensor, and hence makes dispersion curve estimation realistic in formerly inaccessible cases.

Development of Impedance Tube to Measure Sound Absorption Coefficient

An acoustic property of textile material can be measured using an impedance tube, is the most popular technique to measure normal sound absorption and transmission loss. This method consuming less time and a very small sample is required to assess the acoustic properties of the materials. Unfortunately, the cost of the impedance tube and software used for measurement is very high. This paper gives information about how to develop a cost-effective impedance tube suitable for researchers. The design, development, and fabrication of the impedance tube suitable for different frequencies with technical details are present here. Information related to some software which can be used to measure sound absorption coefficient also provided. To validate the testing results obtained from custom-build impedance tube, same samples were tested on commercially available impedance tube at PSG College, Coimbatore. It was observed that both the instruments provide almost same results, no statistically significant difference found in results. Base on the results design of customized impedance tube recommends to student and researcher interested in measuring acoustic properties of textile material.

A non-parametric fluid-equivalent approach for the acoustic characterization of rigid porous materials

• Acoustic characterization of rigid porous materials by using a non-parametric methodology. • Use of a more general approach that overcomes some of the parametric models limitations. • A simple technique that uses only a reduced number of experimental measurements, avoiding complex equipment configurations. • Extensible methodology, easily adaptable to multilayer systems in order to characterize thin or light layers. The acoustic characterization of porous materials with rigid solid frame plays a key role in the prediction of the acoustic behavior of any dynamic system that incorporates them. In order to obtain an accurate prediction of its frequency-dependent response, a suitable choice of the parametric models for each material is essential. However, such models could be inadequate for a given material or only valid in a specific frequency range. In this work, a novel non-parametric methodology is proposed for the characterization of the acoustic properties of rigid porous materials. Unlike most widespread methodologies, this technique is based on the solution of a sequence of frequency-by-frequency well-posed inverse problems, thus increasing the characterization accuracy. Once a reduced number of experimental measurements is available, the proposed method avoids the a priori choice of a parametric model.

Impact of plasma treatment on acoustic properties of natural cellulose materials

Low-temperature plasma is widely used in many surface treatment technologies for modifications of the physical properties of different polymeric materials. In the present work, we have examined the modification of acoustical properties of natural cellulose materials (cotton, hemp) by the radio-frequency argon plasma. We have observed an increase of the sound absorption coefficient due to the plasma treatment for certain range of applied powers. An analysis of elementary processes which happened during plasma–material interaction was conducted. Additional analyses related to material characterizations were performed in order to resolve structural and chemical changes of plasma treated materials. The micro-mechanical modification of treated materials, which happened upon the retrieved structural and chemical changes, was related to the modification of its acoustical properties in order to explain the observed effect.

Usage of Recycled Technical Textiles as Thermal Insulation and an Acoustic Absorber

The sound absorption coefficient is a commonly used parameter to characterize the acoustic properties of materials. The fire performance of construction products has to be evaluated on the basis of their reaction to fire performance. The evaluation of the reaction to fire performance for the flammable construction materials which are in Class E reaction to fire is based on the ignitability test and the thermal test using the radiant heat source. For this study, nine types of STERED® products, which were made from the recycled automotive technical textiles, were chosen in order to evaluate their ability for sound absorption and the reaction to fire. The fire performance was evaluated on the basis of the relative mass loss in the radiant heat source test; the ignitability in accordance with ISO 11925-2, the possible appearance of flame, duration of flame, and the glowing during the single flame source test. The sound absorption of nine products was rated on the basis of the sound absorption coefficient and the noise reduction coefficient. The measurement was performed using the transfer function method in accordance with ISO 10534-2. From the nine tested types of STERED® products, the product Senizol AT XX2 TL 60 had the lowest mass loss at thermal loads up to 700 °C and it fulfilled the conditions for Class E reaction to fire. This product had the highest noise reduction coefficient of 0.81 and a high absorption coefficient for frequencies ranging between 500 Hz and 2000 Hz. The STERED® product Senizol AT XX2 TL 60, as well as Senizol AT 22 TL 50, Senizol AT 40 TL 25, Senizol AT XX4 TL 50 and Senizol AT XX4 TL 10 with a sound absorption coefficient α of between 0.80 to 0.95 and corresponding NRCs from 0.66 to 0.81, these STERED® products can be classified according to ISO 11654 into the sound absorption classes A and B.

Measurements of acoustic impedance of porous materials using a parametric loudspeaker with phononic crystals and phase-cancellation method

When measuring the acoustic properties of architectural materials in a free field or in situ, reflections from the surroundings of the target material and diffraction from the sample edges often generate significant measurement errors. In this paper, a method for measuring acoustic properties by using a parametric loudspeaker, which is superdirective due to the nonlinearity of superhigh-pressure ultrasound, is proposed to overcome this problem: its strong directivity can reduce undesired waves by focusing the sound onto a narrow spatial range. However, such a superstrong ultrasound generates pseudo sound on the microphone surface and increases the measurement errors. Hence, two different strategies, acoustic filtering via phononic crystals and phase-cancellation excitation of the ultrasound, are experimentally investigated to reduce such induced errors. They are also used to evaluate the surface impedance of glass-wool boards at oblique incidence is measured in a free field and in situ. The results show that the proposed method can efficiently measure the surface impedance at frequencies higher than 800 Hz.