Incident Sound Wave Research Articles

Application of a sound-conducting polymer foil for calibration of hydrophones by optical interferometry

Modern calibration of hydrophones at megahertz frequencies is based on the method of optical interferometry, in which the vibrational velocity of an acoustic wave is measured using a thin sound-transparent polymer foil (membrane), metallized on one side to improve light reflection and installed in an ultrasonic field, followed by its replacement with a hydrophone to be calibrated. The main problem of implementing this calibration method is to assess the adequacy of tracking vibrations of the metallized side of the foil to vibrational displacements of water particles under the action of a sound wave incident on the opposite side of the foil. On the basis of the simplified theory of acoustic plane waves passing through layers of dissimilar materials, methods for measuring the speed of sound in the applied foil and an algorithm for calculating the frequency dependence of the sound wave transmission coefficient (in terms of vibrational velocity) from water through the foil to water or air, introduced as a correction to the results of hydrophone calibration, were developed. The uncertainty of the introduction of this correction is estimated.

Рассеяние наклонно падающей плоской звуковой волны упругим цилиндром с неоднородным покрытием, находящимся вблизи плоской поверхности

В статье рассматривается задача о рассеянии плоской монохроматической звуковой волны, падающей произвольным образом на упругий круговой цилиндр с радиальнонеоднородным покрытием в присутствии плоской поверхности (абсолютно жесткой и акустически мягкой). Методом мнимых источников с применением теорем сложения для цилиндрических волновых функций получено аналитическое решение задачи. Волновые поля в содержащей среде и однородном упругом цилиндре находятся в виде разложений по волновым цилиндрическим функциям, а для нахождения полей смещений в неоднородных покрытиях построена краевая задача для системы обыкновенных дифференциальных уравнений второго порядка.Проведены численные расчеты частотных и угловых характеристик рассеянного поля для упругих однородных цилиндров с покрытием и без него, находящихся вблизи подстилающей плоскости. Выявлено существенное влияние непрерывно-неоднородных упругих покрытий на звукоотражающие свойства упругих цилиндрических тел.

Microscopic fluid dynamics of a wire screen bound to a slit resonator excited by acoustic waves

The microscopic fluid dynamics of a wire screen bound to a slit resonator excited by incident sound waves of different intensity are investigated numerically. The microscopic flow features help in understanding the acoustic behavior. A normal impedance-tube model is used in this investigation, and the wire mesh is modeled as an array of eight identical tiny circular cylinders arranged in parallel. Tonal waves of different sound pressure levels and frequencies are introduced from the termination of the tube through a non-reflecting boundary condition. Direct numerical simulations are carried out to solve for the flow and acoustic fields simultaneously, and the velocity and vorticity fields around the resonator are resolved. Upon closer inspection, the tiny cylinders suppress the vortex shedding from the slit excited by high-intensity incident sound waves, thereby retarding the nonlinear acoustic behavior of the slit. Furthermore, the wire mesh contributes greatly to the absorption of acoustic energy through scrubbing loss and flow separation. The acoustic impedance and absorption coefficient are derived using a two-microphone method. The numerical results show that the wire mesh increases the resistance of the resonator significantly while hardly affecting its reactance.

A phenomenological extended-reaction boundary model for time-domain wave-based acoustic simulations under sparse reflection conditions using a wave splitting method

In environmental acoustics and in room acoustics, many surfaces exhibit extended-reaction (ER) behavior, i.e., their surface impedance varies with the angle of the incident sound wave. This paper presents a phenomenological method for modeling such angle dependent surface impedance properties in time-domain wave-based simulations. The proposed method has two attractive features: 1) it is general and can be used to model any type of surface as long as the angle dependent surface impedance is known, and 2) it adds little computational cost to the simulation. The method relies on the assumption of a low reflection density, rendering it suitable for modeling, e.g., outdoor sound propagation and early reflections in large rooms. A wave splitting technique is used to separate the reflected wave from the incident wave at the boundary for each time step of the simulation. Once separated, the angle of the incident sound field is determined and the surface impedance adjusted accordingly. The proposed method is validated analytically and experimentally for a single reflection case with different porous sound absorbers. A clear improvement in accuracy is observed, as compared to locally reacting boundary conditions.

Tunable acoustic jet generated by a masked cylindrical lens

An acoustic jet generated by a mesoscale particle has been proved to be able to achieve sub-wavelength focusing. In this work, we propose two kinds of mask structures to accurately modulate the characteristics of the acoustic jet, such as the focal distance, FWHM and decay length by adjusting the position of incident sound waves. Our simulations show that an ultra-narrow beam waist width (λ/3) in the near field and an ultra-long beam (7λ) in the far field can be achieved under plane wave illumination. This structure provides a simple method to precisely control the acoustic jet.

Switchable asymmetric acoustic transmission based on topological insulator and metasurfaces

Dynamically switching the symmetric and asymmetric acoustic transmission (AAT) is significant in sound manipulation. In this paper, we present the design of switchable AAT in a certain frequency band, which is composed of an acoustic valley hall (AVH) topological insulator and acoustic metasurface (AMS). The underlying mechanism of AAT is attributed to the valley-selective excitation of AVH edge modes and the arbitrary refraction angle controls of the AMS. The acoustic transmission can only occur when the AVH edge modes are excited by controlling the direction of the incident sound waves with the help of AMS. By moving the AMS, the device can shift from symmetric transmission to asymmetric transmission within the designed frequency band. Importantly, the acoustic transmission through the device is topologically protected, which is robust to bends and defects. The AMS based on the spiral-coiling structure is chosen to reach a high acoustic transmission. The performance of switchable AAT is validated with full-wave simulations. Our work may open a new method for introducing the advantages of topological insulators to AAT.

On spatially varying acoustic impedance due to high sound intensity decay in a lined duct

Direct numerical simulations (DNS) based on advanced computational aeroacoustic (CAA) methods are conducted to study the acoustic impedance of a uniformly distributed multi-slit liner under grazing incident sound waves at different frequencies and sound pressure levels (SPL), in the absence of mean-flow. The liner consists of a series of fifteen identical slit Helmholtz resonators. Numerical results show that a portion of the slit resonators in the upstream works in a non-linear regime and the others in the downstream work in a linear regime when high intense waves near the resonance are excited. It is a direct evidence that the acoustic impedance is non-uniform and spatially varying over the liner length due to the different local incident sound pressure levels. With the numerical data, two methodologies are adopted to determine the acoustic impedance of the liner, one is referred to as the Prony's method and the other one is based on an inverse method. The impedance value is validated by a time-domain linearized Euler equation (LEE) solver. Numerical results indicate that representing the liner with a homogenized impedance leads to considerable errors in the reconstructed sound fields when the liner experiences a transition from non-linear regime to linear regime. On the other hand, in cases where such a transition is absent, the homogenized constant impedance is adequate to estimate the acoustic response of the liner. Therefore, a spatially piece-wise function is derived and calibrated by the DNS results to take into consideration both the resistance and reactance variation in stream-wise direction. Comparison shows that the prediction of the sound field is improved by the space-dependent impedance boundary.

Broadband and broad-angle asymmetric acoustic transmission by unbalanced excitation of surface evanescent waves based on single-layer metasurface

Currently, complicated structure, incident-angle selectivity, and narrow frequency band are the key drawbacks of the asymmetric acoustic transmission (AAT) devices. Here we tackle these problems by proposing a class of single-layer lossy acoustic metasurfaces. The broadband AAT performance is realized in a broad range of incident angles. When the incident angle is in the range between two critical values, which are derived in this paper, an external sound wave can be converted into an evanescent mode, and the total internal reflection occurs for backward sound. The incident sound wave can be negatively refracted for forward sound if the evanescent mode conversion condition is broken, representing the realization of the AAT. However, the AAT phenomenon cannot be observed outside of the range defined above. The proposed design of highly efficient broad-angle AAT can find applications in sound sensing and noise control.

Giant extraordinary transmission of acoustic waves through a nanowire.

Wave concentration beyond the diffraction limit by transmission through subwavelength structures has proved to be a milestone in high-resolution imaging. Here, we show that a sound wave incident inside a solid over a diameter of 110 nm can be squeezed through a resonant meta-atom consisting of a nanowire with a diameter of 5 nm equal to λ/23, where λ is the incident acoustic wavelength, corresponding to a transmission efficiency of 500 or an energy densification of ~14,000. This remarkable level of extraordinary acoustic transmission is achieved in the absence of ultrasonic attenuation by connecting a tungsten nanowire between two tungsten blocks, the block on the input side being furnished with concentric grooves. We also demonstrate that these "solid organ pipes" exhibit Rayleigh end corrections to their effective longitudinal resonant lengths notably larger than their in-air analogs. Grooves on the output side lead to in-solid directed acoustic beams, important for nanosensing.

Free and forced bending vibrations of a thin plate in a perfect compressible fluid with energy dissipation taken into account

AbstractA refined statement of stationary dynamic acoustoelasticity problems of thin isotropic plates surrounded from both sides by acoustic media assumed to be perfect compressible fluids has been studed. The problem statement takes into account the energy dissipation in the material of the plate and fluid on the basis of the Kelvin‐Voigt hysteresis model. The refinement of the fluid behavior is based on the assumption that the pressure increment is proportional not only to volumetric strain, but also to the rate of its volumetric strain. This assumption allows us to obtain the generalized Helmholtz wave equation by introducing Skudrzyk's complex sound velocity into consideration to take account of the energy dissipation. The motion equations of the plate are based on the classical Kirchhoff‐Love model and are obtained in two versions. In the first version unsimplified three‐dimensional wave equations are used to determine the aerohydrodynamic load acting on a plate. The second version is based on simplifying the equations of fluid motion by the introduction of the well‐known hypothesis of plane reflection and emission of sound waves. On the basis of the derived equations, exact analytical solutions of two types of problems are obtained. The first type is related to the problem of free vibrations of a rectangular plate hinged around the contour when complex eigenfrequencies were defined. The second type is related to the problem of forced vibrations of the plate under the action of a flat mono‐harmonic incident sound wave when sound transmission loss, the stress‐strain state parameters of the plate as well as the laws of change in sound pressure in a fluid were determined. It is shown that correct and more meaningful solutions of acoustoelasticity problems of the considered class are possible only in case of describing the behavior of a fluid with unsimplified three‐dimensional wave equations with consideration of the energy dissipation.

Experimental and Numerical Assessment of Local Resonance Phenomena in 3D-Printed Acoustic Metamaterials

Abstract The so-called locally resonant acoustic metamaterials (LRAMs) are a new kind of artificially engineered materials capable of attenuating acoustic waves. As the name suggests, this phenomenon occurs in the vicinity of internal frequencies of the material structure and can give rise to acoustic bandgaps. One possible way to achieve this is by considering periodic arrangements of a certain topology (unit cell), smaller in size than the characteristic wavelength. In this context, a computational model based on a homogenization framework has been developed from which one can obtain the aforementioned resonance frequencies for a given LRAM unit cell design in the sub-wavelength regime, which is suitable for low-frequency applications. Aiming at validating both the proposed numerical model and the local resonance phenomena responsible for the attenuation capabilities of such materials, a 3D-printed prototype consisting of a plate with a well selected LRAM unit cell design has been built and its acoustic response to normal incident waves in the range between 500 and 2000 Hz has been tested in an impedance tube. The results demonstrate the attenuating capabilities of the proposed design in the targeted frequency range for normal incident sound pressure waves and also establish the proposed formulation as the fundamental base for the computational design of 3D-printed LRAM-based structures.

Effects of wind-generated bubbles layer on sound propagation underneath rough sea surface in shallow water

The reflection coefficient of the flat sea surface in the ideal condition to the incident sound wave is –1. The perfect reflection effect does not introduce reflection loss. However, the sea surface is usually rough due to the wind. The wind-generated rough sea surface has not only reflection effect, but also scattering effect on the sound wave. At the same time, the wind-generated bubbles layer also has significant effect on the sound propagation. On the one hand, the bubbles layer can change the sound speed profile and result in the refraction of the incident sound wave. On the other hand, the bubbles layer has scattering effect and absorption effect on the incident sound wave and leads to the sound wave to attenuate. In fact, the rough sea surface and the bubbles layer are two main factors affecting the sound propagation in the windy weather at sea. Many researchers have paid much attention to the effect of the wind-generated rough sea surface on the sound propagation, but few of them have considered the effect of the wind-generated bubbles layer on the sound propagation. Based on the Ramsurf sound propagation model under the rough sea surface, the effects of wind-generated bubbles layer underneath rough sea surface on reflection loss and sound propagation with different wind speeds are analyzed. Based on the Hall-Novarini bubbles population model, the sound speed profile in the bubbles layer is modified and the attenuation coefficient due to scattering and absorption of the bubbles layer is calculated. The simulation results shows that when the wind speed is 10 m/s, the effect of the bubbles layer is significant on reflection loss with the frequencies higher than 2 kHz. In the given underwater acoustic environment, for a frequency of 3 kHz, when the source depth and the receiver depth are both 7 m, the enhancement of the transmission loss due to the bubbles layer is 2.6 dB for a wind speed of 13 m/s, and the enhancement is 8.1 dB for a wind speed of 16 m/s. And when the source depth and the receiver depth are both 18 m, the enhancement of the transmission loss due to the bubbles layer is 2.5 dB for a wind speed of 13 m/s and the enhancement is 4 dB for a wind speed of 16 m/s.

Bayesian CNN for Segmentation Uncertainty Inference on 4D Ultrasound Images of the Femoral Cartilage for Guidance in Robotic Knee Arthroscopy

Ultrasound (US) imaging is a complex imaging modality, where the tissues are typically characterised by an inhomogeneous image intensity and by a variable image definition at the boundaries that depends on the direction of the incident sound wave. For this reason, conventional image segmentation approaches where the regions of interest are represented by exact masks are inherently inefficient for US images. To solve this issue, we present the first application of a Bayesian convolutional neural network (CNN) based on Monte Carlo dropout on US imaging. This approach is particularly relevant for quantitative applications since differently from traditional CNNs, it enables to infer for each image pixel not only the probability of being part of the target but also the algorithm confidence (i.e. uncertainty) in assigning that probability. In this work, this technique has been applied on US images of the femoral cartilage in the framework of a new application, where high-refresh-rate volumetric US is used for guidance in minimally invasive robotic surgery for the knee. Two options were explored, where the Bayesian CNN was trained with the femoral cartilage contoured either on US, or on magnetic resonance imaging (MRI) and then projected onto the corresponding US volume. To evaluate the segmentation performance, we propose a novel approach where a probabilistic ground-truth annotation was generated combining the femoral cartilage contours from registered US and MRI volumes. Both cases produced a significantly better segmentation performance when compared against traditional CNNs, achieving a dice score coefficient increase of about 6% and 8%, respectively.

Experimental Study of the Cells Interaction on Linear and Nonlinear Operating Modes

In this article, the results of SAS samples laboratory research on an interferometer with a normal sound wave incidence at sound pressure levels of 100 and 130 dB are presented. The mutual influence of prismatic resonators was revealed, which leads to a decrease in the resonators group acoustic efficiency.

ИССЛЕДОВАНИЕ ВЗАИМОВЛИЯНИЯ ЯЧЕЕК РАЗНЫХ ФОРМ НА НЕЛИНЕЙНЫХ РЕЖИМАХ РАБОТЫ

A rapid development of civil aviation and air transportation market is going on in the XXI century, which is a catalyst for the growth of urban and regional economies. At the same time, the negative impact of aviation on the environment is intensifying, especially in the near-aerodrome territories. The ecology of aviation has become the second most important issue highlighted by the International Civil Aviation Organization, giving way to safety only. One of the dominant components of the aviation harmful effects on the environment is the noise created by the aircraft on the ground. The International Civil Aviation Organization is constantly tightening international standards for aircraft noise on the ground, normalizing its level on take-off and landing modes, forcing aircraft manufacturers to develop new aircraft noise reduction technologies. One of the main components of aircraft noise is the noise generated by propulsion systems. To successfully solve the problems of reducing the aircraft engine noise in a given frequency range, it becomes necessary to conduct complex computational and experimental research to evaluate and optimize sound attenuation in model channels. In addition, it is necessary to research the Helmholtz resonator and SAS parameters effect on the impedance, taking into account the acoustic mechanisms laws and non-linear processes of interactions between the noise and the channel walls. Based on the research, it is necessary to develop new effective forms, hybrid layouts and sizes of the SAS resonant cells. In the present work, physical and mathematical models were formulated for predicting the effective acoustic characteristics of cone-shaped resonators in non-linear operating modes. The results of computational and experimental research of cone-shaped sound-absorbing structures samples on an interferometer with a normal sound wave incidence at a sound pressure level of 130 dB are presented. It was revealed that during the joint operation of cone-shaped resonators, the effect of mutual influence on the SAS nonlinear operating modes was not observed. It was found that the combination of a cone-shaped and an inverted cone-shaped resonator leads to a significant increase in broadband in the SAS non-linear operating modes. The acoustic efficiency of coneshaped resonators was experimentally confirmed. The verification of the developed models was carried out.

Vibro-acoustic performance and design of annular cellular structures with graded auxetic mechanical metamaterials

An exciting paradigm in the ongoing development of materials is the development of auxetic mechanical metamaterials, which can be flexibly designed to exhibit a unique range of physical and mechanical properties. Inspired by nonuniform or nonhomogeneous metamaterials and structures, annular cellular structures composed of auxetic metamaterials with graded negative Poisson's ratios (NPRs) are studied, and the considered models are divided into two types of configurations: models with graded decreasing NPRs and models with graded increasing NPRs along the radial direction. The spectral element method (SEM) is applied to accurately predict the structural dynamic responses with a limited number of elements and the system scale for arbitrary frequencies. The static stiffness and vibro-acoustic performance of the proposed structures are investigated and compared. The computational results show that the bending stiffness, vibrating mode shapes and deformations, and sound transmission loss (STL) of the considered cellular structures are strongly affected by the arbitrarily patterned graded auxetic metamaterials. Within the studied STL frequency range from 1 to 1500 Hz, optimal designs of the conventional and graded configurations for the maximum STL are obtained for specified tonal and frequency band cases under cylindrical incident sound waves. The results show that the graded configurations have more potential than the conventional ones for optimal acoustic performance and that compared with the graded decreasing NPR models, the graded increasing NPR models exhibit STL increases of 6.73 dB, 1.22 dB, and 2.06 dB for the studied cases. Both the STL and optimal design results indicate the advantages of the graded increasing NPR models for use in acoustic attenuation applications. Thus, graded auxetic metamaterials offer a great opportunity for achieving unusual vibro-acoustic performance and extending the route to obtain an optimized set of physical properties for cellular metamaterials and structures.

Nonlinear sound absorption of ultralight hybrid-cored sandwich panels

Abstract A combined experimental, numerical and analytical approach is employed to investigate the nonlinear effect of incident sound pressure level (SPL) on the sound absorption performance of a novel ultralight sandwich panel with perforated honeycomb-corrugation hybrid (PHCH) core. Built upon the motion, continuity and heat conduction equations for compressible viscous fluids, the numerical model fully considers the nonlinear effects caused by incident sound wave with high SPL. The analytical model is constructed by using an approximation solution to the characteristic impedance of micro-perforated panel (MPP) absorbers with consideration of the compressibility of the fluid inside the perforation. The validity of both the numerical and analytical models is checked against experimental measurement results. The effects of facesheet thickness, corrugation thickness and core height on sound absorption are systematically explored. The proposed PHCH sandwich construction is ultralight. It has small total thickness and possess simultaneous load-bearing, energy absorption and sound absorption properties, showing great potential in multi-functional applications. This work provides a nonlinear analytical model and a nonlinear numerical method for the sound absorption of the ultralight hybrid-cored sandwich structures, which demonstrates their superior performance against sound with high SPL.

Sound transmission through truncated conical shells

A theoretical model is presented to investigate the sound transmission through a thin-walled truncated circular conical shell excited by an oblique incident plane sound wave, which impinges on the outer surface of the shell. Love’s theory is used to implement the governing equations of the shell motion, and a convergent power series solution is applied to obtain the exact dynamic response of the shell. In order to calculate the acoustic pressure loadings acting on the shell surfaces, the shell is divided into several narrow segments which can be considered to be locally cylindrical. At first, the model predictions are compared with their experimental and analytical counterparts reported in the literature. Then, the effects of crucial design parameters including different boundary conditions at the ends of the shell, cone angle, incident sound wave angle, length, radius, thickness and material properties of the shell, and the material properties of the fluid media are studied on the characteristics of the sound transmission loss. The proposed model can provide an effective tool in the acoustic design stage of the truncated circular conical shells.

Possibility of Acoustic Resonance in Hair Cells in Human's Auditory System.

Apart from Von Békésy's traveling wave theory, this paper introduces our new comprehension on auditory system based on acoustic resonance in hair cells. Focusing on a rootlet inductance L and a membrane capacitance C of the hair cell, a real-sized cell model is designed so as to form a series LC resonant circuit for the incident soundwaves. In simulation, acoustic resonance is observed successfully at 1120 Hz together with 148-times sound pressure enhancement inside the cell. This model is useful to explain OAE responses, frequency shifts of absolute pitch for aging, pure-tone tinnitus, and even apoptosis of outer hair cells by huge sound exposure.

IMPROVEMENT OF NOISE SILENCER ARMORED VEHICLE KRAZ “BASTION” APPLICATION OF THE GAS SCREEN

Ukraine has been fighting for five years in the east with the Northern Neighbor and for much more time striving for NATO membership. Under these circumstances, the ongoing improvement of military technology. Creation of modern armored cars is topical. One of the important requirements for them – high masking properties. In addition to visual masking there is also sound. In this case, it means reducing the external noise of armored cars. The source of noise and ways to reduce them is a lot. One of the most powerful sources of armored car noise is the noise of the release system, the noise of the bedroom. This type of noise is reduced by means of silencers. The latter are diverse in terms of designs, principles of operation, frequency characteristics and acoustic efficiency. The increase of the acoustic efficiency of silencer noise of the car internal combustion engines was proposed using a gas screen, which until now was used only in aircraft engineering. The essence of the proposal is to create around the outlet branch muffler gas flow, the speed of which is higher than the speed of the outflow of bedrooms. Due to this, the sound waves contained in the sleeping bags will not be able to go into the environment, passing through an additional gas stream, and they will fall onto a special sound absorbing plate. Correspondingly, the sponges will be reflected from this plate and will go to the environment. In this work, for example, the KrAZ Armored Vehicle “Bastion” shows the projected increase in the acoustic efficiency of the existing silencer through the use of a gas screen for the speed of the armored vehicle 45, 50, 75 and 85 km / h. At the same time, the dependence of the difference in speeds of artificially created gas flow and the beds in the muffler of noise from the angle of incidence of sound waves in the flow of bedrooms was calculated. Also shown is the dependence of the angle of incidence of sound waves on the frequency of the latter. Improvement of the existing muffler noise of the internal combustion engines through the use of a gas screen is projected to reduce the external noise of the KrAZ “Bastion” car at 4-6 dB in the range of 45-85 km / h. Keywords: armored vehicle, internal combustion engine, silencer, exhaust gases, noise, noise source, acoustic efficiency, gas screen.