Reflection Of Acoustic Waves Research Articles

Reflection of Acoustic Wave from the Boundary of a Two-Fraction Polydisperse Gas Suspension

The problem of normal incidence of an acoustic wave on the interface between a pure gas and a gas suspension is considered. The case of gas suspension consisting of two fractions, each of which is polydisperse and is described by a certain size distribution function of inclusions has been studied. The dependences of the phase velocity and reflection coefficient on the frequency of perturbations are calculated. The influence exerted by the size distribution function of inclusions, as well as by the mass content on inclusions of the dependences of the reflection coefficient on the frequency of perturbations has been established.

Characteristics of the Reflection and Refraction of Acoustic Waves at Normal Incidence on the Interface between “Pure” and Bubbly Liquids

Characteristics of the Reflection and Refraction of Acoustic Waves at Normal Incidence on the Interface between “Pure” and Bubbly Liquids

Transmission enhancement through arbitrary layers with bianisotropic metasurfaces

Acoustic metasurfaces are thin, engineered structures that can control the local reflection and transmission coefficients of acoustic waves. Here, we describe our recent framework on general impedance matching with bianisotropic metasurfaces, in which elements are designed to control the local asymmetric impedance matrix. Compared with conventional quarter wavelength impedance matching layers, our proposed metasurface, with arbitrary thickness, can maximize wave transmission through an arbitrary layer with controlled phase. As a showcase, we demonstrate the design of a metasurface that helps ultrasound in water to penetrate a steel plate with almost 100% power efficiency and controlled transmission phase, which is beyond what is possible with conventional impedance matching layers. Our approach also applies to electromagnetic scenarios to help waves transmitting through walls or even metal plates.

Borehole interface converted electromagnetic wave of double cylindrical formation

In recent years, electrokinetic effect has received wide attention. The electrokinetic effect refers to the coupling and conversion of acoustic waves and electromagnetic waves in a porous medium. Due to the electric double layer structure of porous medium, electromagnetic waves are generated during acoustic waves propagation in the liquid-containing porous medium. Based on this phenomenon, one proposes a method for electrokinetic effect logging.The electrokinetic effect has great application prospects in earthquake prediction and engineering exploration. The generation mechanism and propagation law of acoustic-electric coupling wave in electrokinetic effect logging of double-cylindrical-layer porous medium are explored in this paper. By calculating the vertical secant integral of the electric field branch point, the total response of the interface converted electromagnetic wave can be obtained. Previously, in the cylindrical layered medium, the secant integral corresponding to the borehole fluid and the inner layer medium branch point is zero. So the examples in this paper are calculated from the vertical secant integral of branch point <i>k</i><sub>em2</sub>, which corresponds to the outermost infinite medium. It is found that when each time the longitudinal and transverse waves of the formation propagate to the interface, the interface converted electromagnetic waves are generated. These converted electromagnetic waves constitute the total response of the interface converted electromagnetic wave. At the same time, the influence of porous medium fluid salinity on interface converted electromagnetic wave is investigated. It is found that when only the inner layer porous medium fluid salinity changes, the amplitude of the interface converted electromagnetic wave response of the two interfaces is affected. When only the salinity of the outermost porous medium fluid changes, only the amplitude of the interface converted electromagnetic wave generated at the second interface is affected, but the interface electromagnetic waves generated at the internal interface are not influenced. When the difference in pore fluid salinity between both sides of the medium interface is larger, the amplitude of the interface converted electromagnetic wave is greater and the electromagnetic waves generated from the two interfaces are independent of each other.The case where fluid intrusion zone in porous medium is investigated, and the generation mechanism of interface converted electromagnetic wave is also studied when only a mineralization interface exists. It is found that the converted electric field is also generated when the acoustic waves propagates to the salinity interface. Since there exists neither multiple refraction of acoustic wave nor reflection of acoustic wave in the porous medium, the interface electromagnetic wave has only two wave packets, which are interface converted electromagnetic waves generated respectively at the borehole wall and at the electrochemical interface.The interface converted electromagnetic wave can be used to detect the location of the medium interface and the salinity interface. It can also clearly reflect the refraction and reflection law of wave propagating in stratified porous medium, which is of great significance for understanding the interface response mechanism of double-cylindrical-layer porous medium in electrokinetic effect logging.

Irregular reflection of spark-generated shock pulses from a rigid surface: Mach-Zehnder interferometry measurements in air.

The irregular reflection of weak acoustic shock waves, known as the von Neumann reflection, has been observed experimentally and numerically for spherically diverging waves generated by an electric spark source. Two optical measurement methods are used: a Mach-Zehnder interferometer for measuring pressure waveforms and a Schlieren system for visualizing shock fronts. Pressure waveforms are reconstructed from the light phase difference measured by the interferometer using the inverse Abel transform. In numerical simulations, the axisymmetric Euler equations are solved using finite-difference time-domain methods and the spark source is modeled as an instantaneous energy injection with a Gaussian shape. Waveforms and reflection patterns obtained from the simulations are in good agreement with those measured by the interferometer and the Schlieren methods. The Mach stem formation is observed close to the surface for incident pressures within the range of 800 to 4000 Pa. Similarly, as for strong shocks generated by blasts, it is found that for spherical weak shocks the Mach stem length increases with distance following a parabolic law. This study confirms the occurrence of irregular reflections at acoustic pressure levels and demonstrates the benefits of the Mach-Zehnder interferometer method when microphone measurements cannot be applied.

Interaction of an acoustic wave with a multilayer medium containing a bubble liquid layer

Discrete-layered media are interesting to research since properties of each layer can significantly differ from near by ones and this can be used in technological processes. The presence of a small number of bubbles significantly increases the compressibility of the medium while the density of the bubble medium remains close to the density of the carrier liquid. From the applied point of view it is interesting that the energy of the incident wave can be completely absorbed by combining of layer properties (length, volume content of the dispersed phase, etc.). In this work, based on the equations of mechanics of dispersed media, we consider the reflection and propagation of acoustic waves passing at right angles through a three-layer medium in a pipeline containing a layer of bubble fluid. From the condition for the existence of a solution in the form of a decaying traveling wave, dispersion relations are written for each of the possible layers. Based on them, the dependences of the amplitude of the incident and transmitted waves on the propagation velocity of the pulse are analytically derived. The coefficients of reflection and transmission through the interface are obtained both in the general case and in particular cases for each layer. These ratios make it possible to calculate the possible consequences of a wave action on the considered media in the event of emergencies at work and to prevent them.

An investigation on efficient acoustic energy reflection of flexible film bulk acoustic resonators

This paper investigates the issues on acoustic energy reflection of flexible film bulk acoustic resonators (FBARs). The flexible FBAR was fabricated with an air cavity in the polymer substrate, which endowed the resonator with efficient acoustic reflection and high electrical performance. The acoustic wave propagation and reflection in FBAR were first analyzed by Mason model, and then flexible FBARs of 2.66 GHz series resonance in different configurations were fabricated. To validate efficient acoustic reflection of flexible resonators, FBARs were transferred onto different polymer substrates without air cavities. Experimental results indicate that efficient acoustic reflection can be efficiently predicted by Mason model. Flexible FBARs with air cavities exhibit a higher figure of merit (FOM). Our demonstration provides a feasible solution to flexible MEMS devices with highly efficient acoustic reflection (i.e. energy preserving) and free-moving cavities, achieving both high flexibility and high electrical performance.

Transmission and absorption in a waveguide with a metamaterial cavity.

The reflection and transmission of acoustic waves along a waveguide of uniform width by a metamaterial cavity is considered. The metamaterial is comprised of a closely spaced array of micro-channels separated by thin plates between which the field may be damped. Exact equations governing the field in the microstructured metamaterial cavity are replaced by an effective field using the homogenisation approach. This allows a solution to be formulated in terms of an integral equation across the interface between the metamaterial cavity and the waveguide. Attention focuses on the resonant and damping effects of a metamaterial cavity of tapered height where rainbow trapping phenomena are encountered. It is shown that near-perfect broadbanded absorption of the incoming wave energy can be achieved.

Analysis and comparison of ion-acoustic wave reflection using laser-induced fluorescence and Langmuir probes

The first laser-induced fluorescence measurements of ion acoustic wave reflection are presented. The experiment is performed in a multi-pole cylindrical chamber using a singly ionized argon (ArII) plasma produced by means of a hot cathode. Ion-acoustic waves are launched from a mesh antenna and reflected/absorbed by a biased, solid boundary (electrode). A comparison between the Langmuir probe and laser-induced fluorescence diagnostics is presented, with complementary Electric-field probe measurements.

Distributed point source modeling of the scattering of elastic waves by a circular cavity in an anisotropic half-space

The Distributed Point Source Method (DPSM) is a modeling technique based on superposition of fundamental solutions corresponding to individual pair of source and target points. A collection of source points distributed over the boundaries and interfaces are responsible for transmission, reflection, and refraction of acoustic waves in the solution domain. The strength of the source points may not be known a priory. By imposing the prescribed conditions on the boundaries and interfaces, a system of equations with the source strengths as the unknowns is obtained. After finding the source strengths as the solution to this system of equation, the amount of the solution at any target point in the domain is obtained by superimposing the effect of all source points on that target point. DPSM is an efficient modeling technique for ultrasonic problems since it does not require discretization of the whole solution domain but only the boundaries and interfaces. The fundamental solution, or the Green’s function, between a pair of source and target points serves as the building block for DPSM. For an ideal fluid or a homogeneous isotropic solid the elastodynamic Green’s function is available as closed form algebraic expressions. But for an anisotropic solids, the set of governing equations are considerably more complex and the elastodynamic Green’s function needs to be evaluated numerically. In this study, an anisotropic half-space containing a flaw in the form of a circular hole is considered. The solid half-space is in contact with fluid and a transducer is located in fluid facing the solid half-space. Some efforts have been made to alleviate the computational intensity of the numerical evaluation of anisotropic Green’s function for this problem. Firstly, a technique called “windowing” is used to exploit the repetitive pattern of relative positions of the source and target points in order to considerably reduce the number of Green’s function evaluations. Secondly, the resolution of the integration for evaluation of the anisotropic Green’s function is changed based on the distance between the source and target points, and a calibration technique based on an equivalent isotropic stiffness tensor is suggested. This calibrated multi-resolution integration technique is combined with the windowing technique, and the developed DPSM model is applied to a numerical example containing a transversely isotropic half-space, to show the applicability and effectiveness of DPSM modeling for this class of problems. Important applications like non-destructive evaluation of composite materials may benefit from such modeling capability.

Nonlinear reflection of weak shock waves from a rough surface in air

Irregular reflection of weak acoustic shock waves occurs under the framework of the von Neumann paradox. In this study, the influence of the surface roughness on the reflection pattern was studied experimentally using spark-generated spherically divergent N-waves of 1.4 cm length reflecting from rigid rough surfaces in air. Dimensions of the roughness were varied from 20 up to 500 μm for different surfaces. A Mach-Zehnder interferometry method was used to reconstruct the pressure waveforms near the surface. The reconstruction was performed by applying the inverse Abel transform to the phase of the signal measured by the interferometer. It was shown that the height of the Mach stem became shorter for surfaces with larger dimensions of the roughness and disappeared when the surface roughness was large enough. Such tendency was also observed in simulations based on the Euler equations where the acoustic source was introduced as a Gaussian-envelope energy injection and the roughness was either sinusoidal or random and described by a Gaussian correlation function. [Work supported by RSF-17-72-10277 and by the Labex CeLyA of Universite de Lyon, operated by the French National Research Agency (ANR-10-LABX-0060/ ANR-11-IDEX-0007).]Irregular reflection of weak acoustic shock waves occurs under the framework of the von Neumann paradox. In this study, the influence of the surface roughness on the reflection pattern was studied experimentally using spark-generated spherically divergent N-waves of 1.4 cm length reflecting from rigid rough surfaces in air. Dimensions of the roughness were varied from 20 up to 500 μm for different surfaces. A Mach-Zehnder interferometry method was used to reconstruct the pressure waveforms near the surface. The reconstruction was performed by applying the inverse Abel transform to the phase of the signal measured by the interferometer. It was shown that the height of the Mach stem became shorter for surfaces with larger dimensions of the roughness and disappeared when the surface roughness was large enough. Such tendency was also observed in simulations based on the Euler equations where the acoustic source was introduced as a Gaussian-envelope energy injection and the roughness was either sinusoidal or r...

Reflection of finite amplitude acoustic wave from a vapor-liquid interface

We numerically investigate the reflection of finite amplitude acoustic wave from a vapor-liquid interface and resulting evaporation or condensation flow induced by the reflected wave on the basis of the kinetic theory of gases. As an initial condition, we consider the finite amplitude plane acoustic wave propagating in a vapor bounded by the liquid layer of the same molecule as the vapor. The governing equation of wave motion in the vapor is the Boltzmann-Krook-Welander equation and the boundary condition at the interface is the complete condensation condition. The Boltzmann-Krook-Welander equation is numerically solved with a finite difference method. As a result, we clarify the reflection law of finite amplitude wave at the interface, which determines an evaporation or condensation flow established after the wave reflection. We numerically investigate the reflection of finite amplitude acoustic wave from a vapor-liquid interface and resulting evaporation or condensation flow induced by the reflected wave on the basis of the kinetic theory of gases. As an initial condition, we consider the finite amplitude plane acoustic wave propagating in a vapor bounded by the liquid layer of the same molecule as the vapor. The governing equation of wave motion in the vapor is the Boltzmann-Krook-Welander equation and the boundary condition at the interface is the complete condensation condition. The Boltzmann-Krook-Welander equation is numerically solved with a finite difference method. As a result, we clarify the reflection law of finite amplitude wave at the interface, which determines an evaporation or condensation flow established after the wave reflection.

Bianisotropic acoustic metasurfaces for wavefront transformation

Acoustic metasurfaces are thin, engineered structures that can control the local reflection and transmission phase of acoustic waves, and thus enable a high degree of flexibility for wave manipulation. Here, we describe our recent work on so-called perfect metasurfaces, in which elements are designed that can control the local transmission and reflection amplitude and phase response of the metasurface. Controlling both the amplitude and the resulting asymmetric phase response requires a fundamentally asymmetric surface impedance for the unit cells. The resulting ideal surface properties thus have strong links to the concept of bianisotropy in electromagnetics and Willis coupling in elastodynamics. We have developed a shunt resonator-based element design that contains the needed degrees of freedom to independently control the surface impedance on both sides of the metasurface. Using this perfect metasurface design approach, we demonstrate the design and experimentally measurement of high efficiency wide-angle transmissive beam steering at levels beyond what is possible with phase control alone.

Numerical observation of secondary Mach stem in weak acoustic shock reflection.

Recently Ram, Geva, and Sadot [J. Fluid Mech. 768, 219-235 (2015)] showed, experimentally, the formation of a secondary Mach stem generated from the reflection of the primary Mach stem in the aerodynamic regime. Such a phenomenon has never been observed, either experimentally or numerically, in the framework of weak acoustic shocks. In this work, the formation of a secondary Mach stem is observed from the reflection of acoustic shock waves on a convex-concave boundary giving rise to a complex five-shock pattern. This study is fully numerical and is based on the numerical solution of a nonlinear acoustic system of equations using a recently developed discontinuous Galerkin solver.

Phase compensation acoustic wave cloak

When acoustic wave is normally reflected from wave thinner medium of semi-infinite, the acoustic pressure phase of reflection wave changes [Formula: see text], or half-wave loss, when acoustic wave is reflected from wave denser medium of semi-infinite, the acoustic pressure phase of the reflection wave is invariant, or no wave loss, when acoustic wave is reflected from wave thinner (or denser) medium of finite thickness, the phase of the reflection wave changes. According to the acoustic wave theory, we derived the acoustic wave reflection coefficient and the phase shift, and designed various kinds of phase shifters. The simulation results show that acoustic phase shifters can cloak acoustic wave.

Immersive Wave Propagation Experimentation: Physical Implementation and One-Dimensional Acoustic Results

A new approach to laboratory acoustic experiments could remove unwanted effects caused by the reflections of acoustic waves from the boundaries of the experimental setup.

Reflection of acoustic waves from the boundary of contaminated fog

The problem of oblique incidence of an acoustic wave from pure air to the boundary of a vapor-gas mixture with droplets of liquid and solid particles is considered. Dependencies of the reflection coefficient of an acoustic wave on the volume content of inclusions and the angle of incidence of a wave are given. The influence of phase transitions is studied.

Acoustic method of atmosphere probing. Modern state and development prospects

Acoustic methods of atmosphere sounding allow us to track the meteorological situation in the atmospheric boundary layer at low costs on-line. The urgency of the these methods development is determined by the need to monitor the environment in conditions of man-caused load increasing. Acoustic waves are much more sensitive to changes in air parameters than electromagnetic waves. However, at present, their effectiveness, compared with laser, thermal and other systems is relatively low. The development of the acoustic sounding method has two directions: the improvement of theoretical descriptions of the interaction of acoustic waves with the atmosphere and the improvement of sounding techniques. Therefore, the evaluation of the most promising paths requires a detailed analysis of the current state, both theoretical foundations and technical implementations of the method. The paper shows that modern acoustic locators are performed at a high technical level and at present the main problem of the method is the lack of an adequate theory of processing the information obtained. The most urgent problems of the method development at the present stage are formulated in the work. They relate to the inverse problems of the fundamental problems of the theory of sound scattering in an inhomogeneous moving medium. Therefore, at present, a number of consecutive progressive steps are required to solve applied problems in the direction of adapting existing achievements to the use in sodar’s systems. Among the urgent tasks that can be developed at the current stage, we can identify the most important. This is a refinement of models of acoustic waves reflection in a stable atmospheric boundary layer in the period of nighttime temperature inversions. Analysis of multi-path probing possibilities for various phase relationships in emitted signals is carried out. Analysis of the prospects for the use of modulated sounding signals is conducted. Naturally, in addition to the above, there are more complex tasks. These include, for example, the reflection analysis in a compressible medium or the optimization of the initial relationships. In practical terms, a clear justification for simplifications in specific tasks is promising.

Delayed-time domain impedance boundary conditions (D-TDIBC)

Defining acoustically well-posed boundary conditions is one of the major numerical and theoretical challenges in compressible Navier–Stokes simulations. We present the novel Delayed-Time Domain Impedance Boundary Condition (D-TDIBC) technique developed to impose a time delay to acoustic wave reflection. Unlike previous similar TDIBC derivations (Fung and Ju, 2001–2004 [1,2], Scalo et al., 2015 [3] and Lin et al., 2016 [4]), D-TDIBC relies on the modeling of the reflection coefficient. An iterative fit is used to determine the model constants along with a low-pass filtering strategy to limit the model to the frequency range of interest. D-TDIBC can be used to truncate portions of the domain by introducing a time delay in the acoustic response of the boundary accounting for the travel time of inviscid planar acoustic waves in the truncated sections: it gives the opportunity to save computational resources and to study several geometries without the need to regenerate computational grids. The D-TDIBC method is applied here to time-delayed fully reflective conditions. D-TDIBC simulations of inviscid planar acoustic-wave propagating in truncated ducts demonstrate that the time delay is correctly reproduced, preserving wave amplitude and phase. A 2D thermoacoustically unstable combustion setup is used as a final test case: Direct Numerical Simulation (DNS) of an unstable laminar flame is performed using a reduced domain along with D-TDIBC to model the truncated portion. Results are in excellent agreement with the same calculation performed over the full domain. The unstable modes frequencies, amplitudes and shapes are accurately predicted. The results demonstrate that D-TDIBC offers a flexible and cost-effective approach for numerical investigations of problems in aeroacoustics and thermoacoustics.

Pressure-based algorithm for compressible interfacial flows with acoustically-conservative interface discretisation

A pressure-based algorithm for the simulation of compressible interfacial flows is presented. The algorithm is based on a fully-coupled finite-volume framework for unstructured meshes with collocated variable arrangement, in which the governing conservation laws are discretised in conservative form and solved in a single linear system of equations for velocity, pressure and specific total enthalpy, with the density evaluated by an equation of state. The bulk phases are distinguished using the Volume-of-Fluid (VOF) method and the motion of the fluid interface is captured by a state-of-the-art compressive VOF method. A new interface discretisation method is proposed, derived from an analogy with a contact discontinuity, that performs local changes to the discrete values of density and total enthalpy based on the assumption of thermodynamic equilibrium, and does not require a Riemann solver. This interface discretisation method yields a consistent definition of the fluid properties in the interface region, including a unique definition of the speed of sound and the Rankine–Hugoniot relations, and conserves the acoustic features of the flow, i.e. compression and expansion waves. A variety of representative test cases of gas–gas and gas–liquid flows, ranging from acoustic waves and shock tubes to shock-interface interactions in one-, two- and three-dimensional domains, is used to demonstrate the capabilities and versatility of the presented algorithm in all Mach number regimes. The propagation, reflection and transmission of acoustic waves, shock waves and rarefaction fans in interfacial flows are predicted accurately, even for difficult cases that feature fluids with shock impedance matching, transonic shock tubes or strong shocks in gas–liquid flows, as well as on unstructured meshes.