Attenuation Of Sound Waves Research Articles

Conditions for sound absorption caused by longitudinal vibration of lightweight powder

It has been reported that powder layers composed of powder materials with a grain diameter of several tens of micrometers exhibit significant sound absorption capabilities in the low-frequency range when the bulk powder density is low. In a previous study, a model considered factors like “powder vibration” and “sound wave attenuation due to gaps between powders.” The remaining challenge lies in the unknown conditions under which a powder with a high sound absorption coefficient is formed through the attenuation of acoustic energy due to the longitudinal vibrations of the powder. In this study, we aimed to estimate these conditions based on the grain size and bulk density. The relationship between the “areal density per grain layer,” expressed as “grain diameter X bulk density,” and the first-order sound absorption peak value revealed that the sound absorption coefficient increases as the areal density per grain layer decreases.

A generic time-frequency analysis-based signal processing and imaging approach for air-coupled ultrasonic testing

The utilization of air-coupled ultrasonic technology is crucial for examining objects that are challenging to establish contact with or cannot endure coupling. Nevertheless, air-coupled ultrasonic is susceptible to various factors such as impedance mismatch, sound wave attenuation, and environmental noise, consequently leading to a diminished signal-to-noise ratio of the received signal. This reduction in signal quality amplifies the complexity of analysis and imaging processes. In this study, a generic air-coupled ultrasonic signal processing and imaging procedure for ultrasonic inspection is proposed, which capitalizes on time-frequency analysis. This methodology attains a heightened level of stability and superior signal-to-noise ratio imaging through a series of procedural steps, encompassing feature extraction, denoising, and the reconstruction of the A-scan signals. The efficacy of the proposed approach is quantitatively assessed in terms of signal-to-noise ratio, probability of detection, robustness, and generality. This innovative method presents a newfangled resolution for automated air-coupled ultrasonic testing.

Heterogeneous attenuation of sound waves in three-dimensional amorphous solids.

Sound waves are attenuated as they propagate in amorphous materials. We investigate the mechanism driving sound attenuation in the Rayleigh scattering regime by resolving the dynamics of an excited phonon in time and space via numerical simulations. We find sound attenuation is spatiotemporally heterogeneous. It starts in localized regions, which identify soft regions within the material and correlate with low-frequency vibrational modes. As time progresses, the regions where sound is primarily attenuated invade the system via an apparent diffusive process.

Vibration Characteristics and Location of Buried Gas Pipeline under the Action of Pulse Excitation

In this paper, the attenuation of sound waves in underground gas pipelines and the vibration characteristics of pipelines are studied, and the feasibility and effectiveness of acoustic measurement of PE pipelines are verified. In this paper, the attenuation equation of sound waves in an underground gas transmission pipeline is derived based on the propagation characteristics of gas and the vibration characteristics of the pipeline itself. In order to verify the experimental results, we conducted an experimental test on the air pipeline model and verified the feasibility and effectiveness of the acoustic measurement of the PE pipeline through the test under the action of pulse excitation. Then, we detect the background noise, design the test scheme according to the characteristics of the buried pipeline, and select the test site for field test. In the test process, we collected the test data and obtained the spectrum diagram of the test data by fast Fourier transform (FFT). By analyzing the results of the spectrogram, we find that the pulse signal can penetrate the medium composed of the pipe formation, but the amplitude of the sound will be sharply attenuated. At the same time, according to the size of the peak in the spectrum, we can determine the location of the pipe. In summary, the feasibility and effectiveness of acoustic measurement of the PE pipeline are verified through experimental tests, and attenuation equations based on acoustic wave propagation characteristics and pipeline vibration characteristics are proposed. It has important practical application value for the safety monitoring and positioning of the buried gas pipeline.

Finite Element Method Assisted Audible Noise Detection for Overhead Line Conductors Using the Cage Experiment

Audible noise (AN) has been the main concern in recent years when considering electromagnetic environmental impact in designing overhead lines (OHLs). Driven by the increased demand of high voltage direct current (HVDC) transmission lines, a novel corona cage experiment is built in association with an acoustic simulation using the finite element method (FEM). The characteristics of the acoustic wave propagation within the testing hall are analyzed using FEM, and the optimized locations for AN detection are determined. On the basis of complying with measurement standards, the location of the measurement is selected to be closer to the sound source and further away from the reflecting surface, to generate more accurate measurement results. In the designated test hall for this paper, the influence of refraction and reflection of sound waves is not obvious. The attenuation of sound waves below 4 kHz is negligible, while for higher frequencies such as 4 kHz and 8 kHz it is significant. Finally, FEM simulation is used to optimize the location for measurement microphones, and further experiments are carried out to verify its accuracy.

Experimental Study on Downhole Acoustic Wave Propagation Characteristics in Curved Drill String

Aiming at the problem of the unclear sound wave attenuation in the signal transmission of the load-bearing drill string, an experimental device for the sound wave propagation characteristics in the curved drill string was set up. The influence of the drill string structure and acoustic excitation parameters on the sound propagation characteristics in the drill string under different loads is different. The results show that the curvature of the drill string has an influence on the propagation of the sound wave in the drill string, and its rule is related to the curvature of the drill string and the frequency of the sound wave. The pulse repetition rate, excitation voltage, and pulse width only affect the passband amplitude, and the effect is significantly greater than the curvature of the drill string. The main influencing factor of its sound transmission characteristics is the degree of drill string curvature. The low-frequency signal should be preferentially selected as the carrier of downhole information transmission after considering the influence of drill string bending on acoustic transmission.

Analysis of Space Charge Signal Spatial Resolution Determined with PEA Method in Flat Samples including Attenuation Effects

The constant development of the electrical engineering sector, especially in the transmission of electrical energy under high-voltage direct current (HVDC), requires research on new insulation materials and investigations of physical phenomena under ultrahigh electrical fields in solid dielectrics. One of the current problematic issues is the formation of space charge in HV insulation systems, which affects the operational electrical field distribution and can lead to faster insulation degradation. There are several problems that have to be considered before every space charge measurement, such as the attenuation and dispersion of sound waves in tested dielectric materials, reflections at the interfaces, and the spatial resolution of the measured charge profile. The spatial resolution is one of the most important technical factors of the PEA measurement stand. The spatial resolution, as it is assumed, depends on several factors, such as the width of the pulser and the pulse rise time, the thickness of the piezoelectric sensor, and the dispersion of the tested material. The article presents the laboratory measurement results of the impact of pulser parameters, such as pulse width and rise time, and sensor thickness on the equivalent thickness of the measured net charge layer corresponding to the resolution of the method. The dispersion in the tested LDPE material is also presented and analysed. The results show that with an increase in the pulser rise time, a higher resolution of the pea method can be achieved.

Kinetic modeling of nonequilibrium flow of hard-sphere dense gases

In nonequilibrium flow of dense gases composed of hard-sphere molecules, a kinetic model is needed to simplify the Enskog equation and reduce computational cost, while also preserving the most important physical properties of high-density gas systems, including the correct transport coefficients. Moreover, density inhomogeneity in the vicinity of a solid boundary, which may influence transport processes, has been overlooked. We have developed such a model using a method based on density functional theory. The inhomogeneous density near the solid wall is found to enhance the oscillation amplitude, while the bulk viscosity causes stronger sound wave attenuation.

Reduction in Airfoil Trailing-Edge Noise Using a Pulsed Laser as an Actuator

Trailing-edge noise (TE noise) is an aeroacoustic sound radiated from an isolated airfoil in the specific ranges of low-speed flow. We used a pulsed laser as an actuator to reduce the TE noise without modifying the airfoil’s surface. The wind tunnel test was conducted to verify the capability of an Nd:YAG laser as the actuator. The laser beam was focused into the air just outside the velocity boundary layer on the lower side of an NACA0012 airfoil. The experimental result shows that the TE noise is suppressed for a certain period after beam irradiations. We then analyzed the physical mechanism of the noise reduction with the laser actuation by the implicit large eddy simulation (ILES), a high-fidelity numerical method for computational fluid dynamics (CFD). The numerical investigations indicate that the pulsed energy deposition changes the unstable velocity amplification mode of the boundary layer, the source of an acoustic feedback loop radiating the TE noise, to another mode that does not generate the TE noise. The sound wave attenuation is observed once the induced velocity fluctuations and consequently generated vortices sweep out the flow structure of the unstable mode. We also examined the effect of the laser irradiation zone’s shape by numerical simulations. The results show that the larger irradiation zone, which introduces the disturbances over a wider range in the span direction, is more effective in reducing the TE noise than the shorter focusing length with the same energies.

Low-Frequency Sound Propagation in an Underwater Waveguide with a Giant Gassy Pockmark

Bottom formations known as pockmarks basically arise due to extensive gas emission. Active pockmarks are characterized by exceptionally high gas saturation and substantially reduced sound speed. The latter circumstance leads to strong attenuation of sound waves contacting with a pockmark. In the present paper, we study low-frequency sound propagation in a 10-km long waveguide crossing a giant pockmark. A new method of acoustic waveguide scanning based on measurement of the wavefield propagator is represented. This method allows one to explore attenuation anomalies associated with the presence of the gas-saturated bottom region. In particular, one can find out which beams fall into a pockmark area and therefore experience strong losses. Identifying such beams, as well as beams which avoid pockmark-assisted losses, one can estimate probable locations of the pockmark segment in the waveguide, provided information about the background medium is sufficient.

Study of Non-Periodical Mechanical Metamaterials: Design and Application

We studied a typical mechanical metamaterial with different geometry patterns to demonstrate its effect in wave transmission. An inclusion geometry described by the trigonometric function is employed to generate local resonance under wave propagation. It has been found that the inclusion geometry plays an important role in the bandgap formation and attenuation of sound wave. More importantly, for a hybrid unitcell, the existing of flat and negative-slope bands indicates the translational mode of the dense core, which is critical to understand the wave reflection through non-periodical metamaterials. Furthermore, we propose a concept of velocity tuning of its individual components, which gives rise to local high strain energy, to explain why the absorptivity of sound wave is high. With help of embedded electronic units and dielectric materials, we can realize the active control of the deformation and reconfiguration of the unitcell, thus, to alter its band structure properties. The fabrication of such metamaterials can be realized by plasma etching, laser printing and nanofabrication from centimeter scale to nanometer scale. Therefore, the applications of mechanical metamaterials can be extended from sound filtering in centimeter scale to thermal management in nanometer scale.

The attenuation mechanism and regular of the acoustic wave on propagation path in farmland soil

Understanding the propagation process of acoustic waves in the soil is very important for designing high-performance acoustic wave detection devices. In this study, the discrete element method was used to simulate the propagation process of acoustic waves in the soil. A single factor experiment was carried out with soil compression ratio, excitation frequency, and excitation amplitude as factors. The influence of various factors on the time and frequency domain were analyzed from the perspective of the received signal and the force signal on the particle. The results showed that: with the increase of soil compression ratio, the speed of the acoustic wave, the amplitude of the received signal's first wave and the dominant frequency increased; with the increase of excitation frequency, the amplitude of the received signal's first wave decreased, and the dominant frequency and speed of acoustic wave remained unchanged; with the increase of excitation amplitude, the received signal amplitude increased, and the dominant frequency and speed of acoustic wave remained unchanged. According to the force signal of the particles on the sound wave propagation path, as the soil compression ratio increased, the dominant frequency of the acoustic wave increased, and the amplitude attenuation coefficient increased; as the excitation frequency increased, the dominant frequency and amplitude attenuation coefficient of the acoustic wave first increased and then decreased; as the excitation amplitude increased, the dominant frequency of the acoustic wave remained unchanged, and the amplitude attenuation coefficient increased. The occurrences of these phenomena were related to the natural frequency of the soil and the sound wave attenuation mechanism. During the propagation process, the dominant frequency of the sound wave would continue to attenuate and eventually reached the natural frequency, resulting in the same dominant frequency of the received signal under different excitation frequencies. Under different parameters, the decay speed of the sound wave amplitude was different, and the initial signal amplitude was different, which led to the various first wave amplitude of the received signal. The conclusion could be drawn through the simulation experiment: the DEM method could well characterize the acoustic wave propagation process in the soil and analyze the acoustic wave propagation law in the soil. Thus, it provides theoretical support and reference for the research and instrument manufacture of the acoustic wave detection of soil characteristics.

Broadband low-frequency sound attenuation in duct with embedded periodic sonic black holes

This paper studies the sound wave propagation and attenuation characteristics in a new type of acoustic device, which is constructed by periodically embedding sonic black holes (SBHs) into an air-filled waveguide. The SBH is realized by cascading a set of rigid rings with linearly or quadratically changing inner radii into each unit cell section. Acoustic impedance variation rendered by this specially tailored profile progressively slows down the incident sound velocity to generate the SBH effects including wavelength compression, energy focalization, and dissipation with inherent damping in the duct. Upon developing and validating a model based on the transfer matrix method (TMM), the sound transmission loss (STL) of a finite-length periodic duct with different geometrical parameters is investigated. Different from a single SBH unit which can trigger the complete SBH process only above the cut-on frequency, the proposed periodic arrangement offers strong attenuation bands in the low-frequency range of the STL curve well below the frequency barrier imposed by the cut-on frequency of a single SBH unit. Mechanism studies reveal that these attenuation bands result from the interplay between the Bragg scattering and the SBH-specific slow-sound effects. The latter is shown to equivalently increase the effective lattice constant of the periodic duct, thus lowering the frequency of the Bragg bandgap. It is also shown that in contrast to conventional locally-resonant metamaterials, the proposed device exhibits far less dependence on the number of unit cells and the amount of rigid rings to activate a significant low-frequency stop-band. These appealing features could greatly simplify the design and application of SBH-based metamaterials, making it a promising solution for low-frequency wave manipulation and noise control.

How the waveguide acoustic black hole works: A study of possible damping mechanisms.

The acoustic black hole (ABH) effect in waveguides is studied using frequency-domain finite element simulations of a cylindrical waveguide with an embedded ABH termination composed of retarding rings. This design is adopted from an experimental study in the literature, which surprisingly showed, contrary to the structural counterpart, that the addition of damping material to the end of the waveguide does not significantly reduce the reflection coefficient any further. To investigate this unexpected behavior, we model different damping mechanisms involved in the attenuation of sound waves in this setup. A sequence of computed pressure distributions indicates occurrences of frequency-dependent resonances in the device. The axial position of the cavity where the resonance occurs can be predicted by a more elaborate wall admittance model than the one that was initially used to study and design ABHs. The results of our simulations show that at higher frequencies, the visco-thermal losses and the damping material added to the end of the setup do not contribute significantly to the performance of the device. Our results suggest that the primary source of damping, responsible for the low reflection coefficients at higher frequencies, is local absorption effects at the outer surface of the cylinder.

Long-range underwater acoustic communication of M-eyry spread spectrum with cyclic prefix

The Spread Spectrum is an effective transmission method for complex channels in underwater acoustic (UWA) communication because of the high correlation of pseudo-random noise (PN) sequence. In particular, the spread spectrum method is effective in an environment with a low signal-to-noise ratio. The bandwidth of UWA communication channel is limited due to the fact that sound wave attenuation in water is positively associated with frequency. The limited bandwidth directly leads to the low data rate of conventional direct-sequence spread spectrum UWA communication. M-ary spread spectrum (MSS) schemes using multiple orthogonal PN sequences were proposed as a solution to this problem. However, even in the MSS method, the performance may be limited by the delay spread characteristics in the multipath propagation channels. We propose a more robust communication method in the UWA channel by including Cyclic Prefix (CP) to achieve a more robust performance in the multipath channel. In the proposed method, a CP is inserted for every symbol. In the 160 km long-range UWA communication experiment conducted in the East Sea, the proposed method showed more reliable results than the conventional MSS method. [Work supported by the Agency for Defense Development, South Korea, Grant No. UD200010DD.]

Comparison of estimated and measured sound-absorption coefficient and transmission loss by geometric dimensions of a collection of equilateral triangular holes of equilateral triangular holes

We performed a theoretical analysis on collection of equilateral triangular holes with consideration for sound wave attenuation within the tube and then calculated the sound-absorption coefficient and transmission loss. We then compared these results with experimental values. In the experiment, we measured the sound-absorption coefficient and transmission loss of a test sample using impedance measurement tubes with two and four microphones. We estimated the sound-absorption coefficient and transmission loss because of the dimensions of a collection of equilateral triangular holes through theoretical analysis and then compared these results with experimental values. In the present analysis, the propagation constant and characteristic impedance were introduced into a one-dimensional transfer matrix. Considering the effects of sound wave attenuation in the tubule from three-dimensional analysis, we derived the propagation constant and characteristic impedance. Values for the sound-absorption coefficient and transmission loss obtained through the analysis of holes as triangles rather than as circles gave calculation results closer to the experimental values. This is because this method more suitably simulates the effects of the boundary layer that occupies the space within the hole. The results show that the sound absorption coefficient and transmission loss of triangular honeycombs can be estimated with sufficient accuracy using only geometric dimensions and physical properties.

Numerical and experimental study on leakage detection for buried gas pipelines based on distributed optical fiber acoustic wave

Buried natural gas pipeline leakage can cause severe environmental pollution and human casualties. The currently used fiber optic temperature sensors cannot detect pipeline leakage in all directions, and there are monitoring blind spots. Besides, there is a lack of field tests and verification of the acoustic characteristics caused by leakage. In this work, a sound wave attenuation model considering gas flow in viscous porous media is established based on the Φ-optical time-domain reflectometry (Φ-OTDR) principle, combined with fluid dynamics and acoustic wave propagation mode in porous media (soil). The attenuation characteristics of acoustic wave propagation in soil are studied by varying the leakage hole size and leakage pressure. It is found that the acoustic source of buried natural gas pipeline leakage belongs to broadband noise. The acoustic signals detected by optical fiber acoustic sensors are vary with different leakage holes and leakage pressures. In particular, the leaked acoustic wave’s energy is prominent in the low-frequency band of 15 kHz, and the sound pressure level (SPL) oscillates and attenuates with the increase in frequency. With the increase in the transmission distance, the amplitude of the pipeline leakage signal gradually attenuates. Eventually, the acoustic wave decays to the point where the fiber-optic acoustic sensor cannot detect it. The optimum frequency of acoustic wave propagation in soil is obtained through experimental research. The propagation characteristics of acoustic waves in the soil are not a fixed value. The simulation results are in good agreement with the experimental results, indicating that the SPL in the low-frequency band is significant for pipeline leakage monitoring. The above research results can provide valuable guidance for field optical fiber installation.

Improved effectiveness of acoustic absorbing materials by using air layers in a one-dimensional tube

Acoustic absorbing materials are used in various applications to reduce noise. In air ducts and pipes, they are used to attenuate noise from devices such as fans. When an absorbing material is installed across the entire cross-section of a duct, sound wave attenuation is large, but so is pressure loss in the flow. For greater effectiveness with less acoustic absorbing material in a one-dimensional tube system, we propose a method in which layers of acoustic absorbing material are separated by air layers and we derive the transmission loss in this method. A parametric study was performed to confirm the effectiveness of the air layers and investigate characteristics of the system. The results show that the method’s effectiveness is due to the antiresonance properties of the air layers. An experiment with an acoustic tube was performed to assess the validity of the proposed method and the derived transmission loss. The experimental and numerical results for transmission loss agree well, indicating the proposed method is effective when acoustic absorbing material layers are used.

Effect of Nanoparticles on Acoustics Properties of Polyurethane Foam

Abstract:Noise pollution is growing in the modern century, with population growth and the advancement of manufacturing, which is the cause of many social and urban anomalies. Also, noise pollution leads to exhaustion and decreased efficiency in the workplace. We first define the sound and its properties in this article, then we discuss polyurethane as one of the most significant members of the polymer family and we examine polyurethane foams among the different types of polyurethane. Sound is a mechanical wave that requires transmitting through an environment. Polymers minimize and remove wave energy by viscous loss due to their viscoelastic properties, especially their viscous regions, and absorb sound. The literature review showed that adding nanoparticles improves the properties of polyurethane foam, especially the acoustic properties of polyurethane foams. By increasing the sound propagation paths through the polymer sample, these nanoparticles increase the likelihood of sound wave attenuation through viscous loss. These nanoparticles are classified into various forms according to the aspect ratio, like plate-like nanoparticles such as graphene and graphene oxide, nanotubes containing carbon nanotubes, and particulate nanoparticles containing metal oxides such as zinc oxide, and nano clays that have been examined by many researchers in polyurethane foam samples to study the effect of each nanoparticle on sound absorption.

Progress of low-frequency sound absorption research utilizing intelligent materials and acoustic metamaterials.

In recent years, increasing attention has been paid to the impacts of environmental noises on living creatures as well as the accuracy and stability of precise instruments. Due to inherent properties induced by large wavelength, the attenuation and manipulation of low-frequency sound waves is quite difficult to realize with traditional acoustic absorbers, yet particularly critical to modern designs. The advent of acoustic metamaterials and intelligent materials provides possibilities of energy dissipation mechanisms other than viscous dissipation and heat conduction in conventional porous sound absorbers, and therefore inspires new strategies on the design of subwavelength-scale structures. This short review aims to trace the current advancement on the low-frequency sound absorption research utilizing intelligent materials and metamaterials, including Helmholtz resonators and acoustic metamaterials based on micro-perforated plates, porous media, and decorated membrane, along with the tunable absorbing structures regulated with the function of electroactive polymers or magnetically sensitive materials. The effective principles and prospects were concluded and presented for future investigations of subwavelength-scale acoustic structures.