Nonlinear Interaction Of Acoustic Waves Research Articles

Modeling and Simulation of Parametric Nonlinear Focused Ultrasound in Three-Dimensional Bubbly Liquids with Axial Symmetry by a Finite-Element Model

This paper presents the development of a numerical model able to track in time the behavior of nonlinear focused ultrasound when interacting with tiny gas bubbles in a liquid. Our goal here is to analyze the frequency components of the waves by developing a model that can easily be adapted to the geometrical restrictions and complexities that come out in several application frameworks (sonochemistry, medicine, and engineering). We thus model the behavior of nonlinear focused ultrasound propagating in a liquid with gas bubbles by means of the finite-element method in an axisymmetric three-dimensional domain and the generalized-α method in the time domain. The model solves a differential system derived for the nonlinear interaction of acoustic waves and gas bubble oscillations. The high nonlinearity and dispersion of the bubbly medium hugely affect the behavior of the finite-amplitude waves. These characteristics are used here to generate frequency components of the signals that do not exist at the source through nonlinear mixing (parametric antenna). The ability of the model to work with complex geometries, which is the main advantage of the method, is illustrated through the simulation of nonlinear focused ultrasound in a medium excited from two spherical sources in opposite directions.

Experimental results of tomographing the third-order acoustic nonlinear parameter

Tomography of the acoustic nonlinear parameters is a method of obtaining information about biological tissue using nonlinear interaction of acoustic waves. In the schemes under consideration, three plane coded non-collinear signals probe an investigated object and intersect inside it. Each point of the intersection region generates coded signal at the third-order combination frequencies. Correlation processing of received total signal allows determining the combination of the second- and third-order acoustic nonlinear parameters in each resolution element of the object. Results of physical experiment on reconstructing the spatial distribution of the combined acoustic nonlinear parameter by the scheme with one monochromatic and two coded probing signals are presented. Principal disadvantage of this scheme is nonlocality of generation area of the unique coded combination signal carrying information about the object. This makes it impossible to distinguish the signal generated by the only fixed resolution element of the object. As a consequence, reconstructed quantitative values of the nonlinear parameters can be distorted. The next step is the scheme with three coded probing signals, that is more complex for implementation. Nevertheless, now each unique signal is generated by the single resolution element. Thereby, it becomes possible to adequately reconstruct the desired values of nonlinear parameters.

Nonlinear Interaction of Acoustic Waves with a Spheroidal Particle: Radiation Force and Torque Effects

The nonlinear interaction of a time-harmonic acoustic wave with an anisotropic particle gives rise to the radiation force and torque effects. These phenomena are at the heart of the acoustofluidics technology, where microparticles such as cells and microorganisms are acoustically manipulated. We present a theoretical model considering a generic acoustic beam interacting with a subwavelength spheroidal particle in a nonviscous fluid. Concise analytical expressions of the radiation force and torque are obtained in the scattering dipole approximation. The radiation force is given in terms of a gradient and scattering force; while the radiation torque has two fundamental contributions, namely, the momentum arm and acoustic spin (spin-torque effect). As a practical example, we use the theory to describe the interaction of two crossed plane waves and a prolate spheroidal particle. The results reveal the particle is transversely trapped in a pressure node and is axially pushed by the radiation force. Also, the momentum arm aligns the particle in the axial direction. At certain specific positions, only the spin-torque occurs. Our findings are remarkably consistent with finite-element simulations. The success of our model enables its use as an investigation tool for the manipulation of anisotropic microparticles in acoustofluidics.

Monitoring of Bioresources in Shallow Water by Parametric Systems

Hydroacoustic parametric systems and methods of nonlinear acoustics in the study of bioresources in shallow areas of the oceans are considered. Unique characteristics of parametric antennas are given. The general issues of nonlinear interaction of acoustic waves are considered. The features of the interaction and propagation of acoustic waves in shallow water are presented. The characteristics of parametric instruments are presented, and the results of their applications for monitoring bioresources in shallow areas of the oceans are considered

Theoretical and experimental study on the acoustic wave energy after the nonlinear interaction of acoustic waves in aqueous media

Based on the Burgers equation and Manley-Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and the pump wave, the analytical solutions of acoustic waves’ amplitude in the field are deduced. The relationship between normalized energy of high-frequency and the change of acoustic energy before and after the nonlinear interaction of the acoustic waves is analyzed. The experimental results about the changes of the acoustic energy are presented. The study shows that new frequencies are generated and the energies of the low-frequency are modulated in a long term by the pump waves, which leads the energies of the low-frequency acoustic waves to change in the pulse trend in the process of the nonlinear interaction of the acoustic waves. The increase and decrease of the energies of the low-frequency are observed under certain typical conditions, which lays a foundation for practical engineering applications.

Dynamic characteristics of nonlinear interaction in elastic medium

Traditionally, an acoustic wave process is analyzed in terms of sound pressure and/or sound velocity. The dynamic distortion of the wave profile, however, is complicated by contribution of both quadratic and cubic nonlinearities of the elastic medium. This condition necessitates expanding a range of variables to include particle and wave accelerations. As dynamic characteristics, particle and wave accelerations fully complement analysis of dynamic and inert properties of the elastic medium. The Riemanns solution, in which the quadratic and cubic nonlinearities are accounted for through respective derivatives of the sound velocity, allows for a new and different perspective on the aforementioned properties. For a simple wave with contribution of the quadratic nonlinearity only, the acceleration profile describing dynamics of wave deformation varies symmetrically relative to the discontinuity region. The cubic nonlinearity leads to more complex acceleration profile with asymmetric properties, which can be discerned and assessed using a combination of numerical and graphical methods. Such an approach is quite effective and vivid in separating contributions of quadratic and cubic nonlinearities. An integral nonlinear parameter N, introduced on the basis of this analysis, is proposed for estimating ability of the fluidlike medium to support effective propagation and nonlinear interaction of acoustic waves.

Reflection and refraction of surface acoustic waves by a periodic domain structure

Reflection and refraction of surface acoustic waves by a periodic domain structure formed in lithium niobate is studied. A second harmonic generation is observed. A mechanism underlying the linear and nonlinear interactions of acoustic waves with a periodic domain structure is proposed.

Subharmonics and noise excitation in transmission of acoustic wave through unconsolidated granular medium

First laboratory-scale experimental observation of both subharmonics excitation and significant increase in noise level caused by propagation of the acoustic wave in unconsolidated granular material is reported. The bifurcation phenomenon, taking place above a critical level of acoustic excitation (and opening the subharmonics route to chaos) is attributed to the interaction of acoustic wave with distributed system of highly nonlinear inter-grain contacts. The estimates demonstrated that these are weak contacts (loaded at least two orders of magnitude weaker than in average) that might be responsible for the observed nonlinear effects. The additional intermittent contacts created by the acoustic wave (which are open in the absence of acoustic loading) can also contribute. In the clapping (tapping) regime, each of these contacts individually is similar to an impact oscillator, for which the scenario of period doubling cascade and the transition to chaotic behavior has been predicted theoretically and observed experimentally earlier. The experiments confirm that the nonlinear interactions of acoustic waves in granular assemblages are highly sensitive to the fraction of weakly loaded (and unloaded) contacts, information on which is difficult to access by any other experimental methods.

Observation of nonlinear interaction of acoustic waves in granular materials: demodulation process

Experimental study of the demodulation effect of ultrasonic waves in glass beads are reported. Both impulsive (burst) and continuous regime have been studied for amplitude modulated signals with its carrier frequency of 100 kHz. It is shown that two low frequency acoustical modes corresponding to the modulation frequency (in the range of few kHz) are excited due to the nonlinear processes in the granular medium. The excitation of a first mode propagating mainly through the beads (solid-based mode) and the excitation of a second mode propagating mainly through the air saturating the granular material (fluid-based mode) are observed. Possible physical mechanisms of generation and regimes of propagation in the granular assemblages are discussed.

Increase of the Transparency of the Ionosphere for CosmicRadiowaves Caused by a Low Frequency Wave

This article is devoted to theoretical and experimentalinvestigations of nonlinear interactions of acoustic waves with theplasma in the ionosphere. It is shown that a low frequency acousticwave excited by means of a ground-based acoustic generator (GAG)causes a periodic structure in the ionosphere and an increase of thetransparency for cosmic radioemission. This phenomenon makes itpossible to simulate the acoustic channel of thelithosphere-atmosphere-ionosphere connection, and to investigate thischannel experimentally by means of acoustic generators. Here wepresent the experiment and the theory which confirm that the acousticchannel is one of the strongest for the passing of energy from thelithosphere to the ionosphere through the atmosphere.

Nonlinear sound–vortex interactions in an inviscid isentropic fluid: A two-fluid model

A new two-fluid model is developed to describe the nonlinear interaction of acoustic waves and vortices. Analytical and computational results are presented for a sound pulse interacting with and being modified by a vortex. A novel numerical method based on a particle-in-cell discretization of the acoustic field is developed and used to study the nonlinear scattering of sound by a cylindrical vortex. Equations for the sound wave packet propagating in an axially symmetric mean flow are integrated analytically. Nonlinear modification of the vortex flow by the high-frequency sound is found to be mediated by growing pressure disturbances generated by the radiative forcing on the high gradient regions of the acoustic pulse. The total energy of the vortex mean flow grows monotonically, as the acoustic component loses its energy. The changes in the kinetic and internal energies of the vortex are greater than the changes in its total energy, although these changes are reversible in lowest order of the nonlinear vortex–acoustic interaction.

Etudes d'interactions acoustiques non-linéaires dans les jets confinés, par la fonction de bicohérence

Self-sustained tones are encountered when a flow passes two orifice plates, sufficiently close together, inside a duct. The upstream orifice plate creates a confined jet which impinges on the edge of the downstream orifice plate. The shear layer oscillations (coherent structures) of the confined jet in the presence of a resonant acoustic field (pipe mode), constitute the main features of cavity tones. The tones are synchronized by the pipe modes. When the flow velocity is varied for a fixed geometry, frequency jumps from one mode to another are observed. Pressure spectra showing intense acoustic energy localised in narrow bands near pipe mode frequencies are measured. We emphasize the existence of transition flow regimes during which quadratic non-linear coupling between spontaneously excited modes can take place. A digital bispectral analysis (bicoherence function) is used to quantify the degree of nonlinear interactions of acoustic waves of finite amplitude in the so-called transition region

Nonlinear interaction of acoustic waves with microwave electric fields in piezoelectric semiconductors

Nonlinear interaction of acoustic waves with microwave electric fields in piezoelectric semiconductors

A Three-Phonon Process in the Electron-Phonon System

A three-phonon process via a nonlinear interaction of acoustic waves with conduction electrons is studied based on the semiclassical Boltzmann equation treatment. The Hamiltonian for this process is given in the form which is easily applied to the discussion of non-Ohmic behaviors observed in CdS and Bi. The order of magnitude of the new process is examined in terms of the effective third-order elastic constant, which depends strongly on the carrier concentration, the wave number and the temperature. In a restricted range of wave number, the new process predominates over the usual three-phonon process due to the anharmonic interaction in lattice vibrations in the following cases: (1) CdS with carrier concentrations 10 12 –10 15 cm -3 , (2) n -Ge with carrier concentration 10 16 cm -3 at low temperatures, (3) Bi in the absence of a magnetic field. In Bi in a strong magnetic field, the magnitude of the new process becomes much smaller than the usual one.