Nonlinear Acoustic Effects Research Articles

Nonlinear acoustic effects induced by propagation of intense ultrasound through liquid

Examination was performed into nonlinear acoustic effects (cavitation, acoustic flow, and radiation pressure) induced by propagation of intense (>0.1 W/cm2) kilohertz-range frequency ultrasonic vibrations through liquids.

Effect of acoustic nonlinearity on the rise-up profile of acoustic streaming

The influence of higher harmonic generation due to acoustic nonlinearity on the rise-up profile of acoustic streaming is investigated. When two driving conditions with different higher harmonic content at identical driving force are set, the behavior of streaming under these conditions is experimentally compared. A thin film is used to eliminate the influence of acceleration. It has been believed so far that streaming rises more quickly as the generation of higher harmonics increases. However, the present analysis concludes that the rise-up profile of acoustic streaming is dependent only on the driving force and is independent of the relative higher harmonic contribution to the driving force. ©1998 Scripta Technica, Electron Comm Jpn Pt 3, 82(2): 66–75, 1999

Evaluation of material degradation using nonlinear acoustic effect

A method to measure the nonlinear effect of ultrasonic waves is suggested as a new approach for the effective evaluation of material degradation. In sonic wave propagation, nonlinear effect can be interpreted as the generation of higher order harmonic waves. The generation mechanism of higher order harmonic components due to nonlinear effect is firstly explained using nonlinear elasticity. Next, we attempt to measure how much higher order harmonic component was generated in the degraded material. For this purpose, a measurement system mainly based on a high power nonlinear ultrasonic signal analysis system that adopts heterodyne signal detection technique was constructed. From the results, we confirm that the nonlinear acoustic effect may be a useful technique for the evaluation of material degradation.

GHz ultrasound wave packets in water generated by an Er laser

A variety of schemes are presented, suitable for the temporally and spatially controlled generation of ultrasound pulses with a centre frequency near 1 GHz. Direct excitation of acoustic waves in water, serving as the coupling and transport medium, relies on the resonant absorption of short erbium laser pulses in water: at the interface with an adjoining solid material or at a free water surface. Ultrasonic amplitudes, leading to nonlinear acoustic effects, have been demonstrated. The photoacoustic excitation methods presented here are suitable for scanning acoustic microscopy, for example for the real-time study of biological cells in vivo.

Self-action of the acoustical wave in glass with cracks

The recently developed nonlinear acoustic method for nondestructive testing uses the modulation of sound by vibrations. However, there are many other nonlinear acoustic effects that could also be used for nondestructive testing. These effects include: amplitude-dependent internal friction, high-amplitude vibration shifting the resonance frequency, generation of higher harmonics, and others. These effects were observed in a glass rod that was fractured by an intensive laser beam, while a similar unfractured glass rod did not exhibit them. The resonance acoustical field in the glass rod was excited on the frequency about 4 kHz and the strain in this field was up to 10−5. Some of the observed effects varied in time, which suggests a change in the crack contact surfaces due to the acoustical field. A theoretical model of acoustic propagation in cracked media to explain the observed nonlinear behaviors is discussed. [This work is supported by the United States Industry Coalition, with the US DOE Contract W-7405-ENG-36, through the University of California.]

Nondestructive flaw detection in a solid medium using nonlinear acoustic effects

In a solid material it is very difficult to find tiny defects or cracks with the conventional linear acoustic techniques as nondestructive evaluation methods. When defects exist in a material, nonlinear acoustic responses become dominant in a propagating medium and can make it possible to detect such defects. As an application of such nonlinear acoustics, a nonlinear acoustic modulation technique for nondestructive flaw detection described in previous work [Kim et al., J. Acoust. Soc. Am. 101, 3029 (1997)] was applied to several different sample materials to confirm its feasibility. The second harmonic measurements can easily indicate existence of tiny defects or cracks in the samples. The time-delay measurements of the modulated sum and difference frequency signals can accurately locate defects in aluminum, steel, and brass solid rods, respectively.

Nonlinear acoustic interactions in liquids with bubbles and their applications for bubble measurements at sea

It is known that, in comparison with homogeneous media (e.g., water, air), acoustical nonlinearity of a liquid with a small concentration of bubbles can be anomalously high. The influence of bubbles upon nonlinear properties of the medium is often much more significant than the simultaneous change of linear characteristics, such as sound speed. This paper presents a brief review of our investigations of nonlinear acoustic phenomena in bubble clouds, and some results concerning nonlinear acoustic methods of measurements of bubble radii and their distribution in water. (1) The theory of the bubble medium is based on summation of the fields scattered by separate bubbles. The scattered field consists of coherent and noncoherent parts, and the latter can be treated as a nonlinear reverberation signal which takes place at frequencies different from those of the incident acoustic wave: second harmonics in the case of a harmonic primary radiator, and sum- and difference-frequency signals for a bifrequency radiator. The formulas relating these signals to the bubble distribution in the layer have been obtained. (2) To observe nonlinear acoustic effects in a subsurface bubble layer and in sea sediments, two echosounders working at different frequencies were used. The sum- and difference-frequency components were observed in the signals scattered from sediments with bubbles and from the subsurface bubble layer. The theory of such nonlinear scattering is in good agreement with experimental data.

Nonlinear acoustic Doppler effect in a bubble flow.

The Doppler effect is a well‐known and widely used phenomenon. In acoustics it is usually considered for linear response from a moving target. No attention was given previously to specific phenomena of nonlinear sound scattering by moving nonlinear scatterers. In the present paper a nonlinear analog of the Doppler effect is studied theoretically and experimentally. The most prominent nonlinear acoustic scatterer is a bubble. A theoretical analysis of frequency shift under nonlinear scattering of two, in a general case, acoustic waves by a moving nonlinear scatterer with generation of harmonics and combination (i.e., the sum and the difference) frequencies is given. It is shown that the nonlinear Doppler frequency shift for the difference frequency generation depends on the geometry of primary waves and can be much larger than the linear Doppler frequency shift for the difference frequency. Experiments have been made with bubble flows in a vessel. The results are in good agreement with the theory. Feasible...

Observation of nonlinear scattering of acoustical waves at a subsurface bubble layer

To observe nonlinear acoustic effects in a subsurface bubble layer, two echo sounders working at different frequencies were used. The experiments were performed in the shallow area of the southern part of the Baltic Sea aboard the research vessel ‘‘Oceania.’’ Two echo sounders were run at 30 and 37 kHz; each had a power of about 0.3 kW. The depth of the echo sounders was about 15 m and the intensity of the acoustic signal in the subsurface bubble layer was enough to observe nonlinear effects. The sum and difference frequency components in the spectra of the scattered signal were determined. A theory of such a nonlinear scattering, based on summarizing the signals scattered by separate bubbles, was developed. It was shown that the sum frequency component was due to a noncoherent reverberation in the bubble layer and the difference frequency component was coherent. This component was generated in the process of primary wave propagation and can be received after sea surface reflection. Experimental and theoretical results have shown that the nonlinear scattering can be used to determine bubble density at sea. [Work was supported by ONR.]

Nonlinear acoustic effects in superfluid 3He-B

We consider the nonlinear interaction of zero sound with the collective modes of the order-parameter in superfluid 3 He-B. The approximate particle-hole symmetry of the 3 He-Fermi liquid determines selection rules for the linear and nonlinear coupling of zero sound to the collective modes. Starting from the quasiclassical theory of superfluid 3 He, we have shown that the coupling strenghts have a simple representation in terms of Feynman diagrams. We predict measurable two-photon absorption and nonlinear-Raman scattering by the J = 2 + (real squashing) modes at low pressures. Recent observations of two-phonon absorption by a group in Helsinki are compared to the theoretical predictions. Two-phonon absorption can be used to determine the dispersion of the J = 2 + modes.

Thermal self-focusing of the acoustic beam in the ferromagnet near the temperature of the orientational phase transition

The possibility of the thermal self-focusing of an acoustic beam in the magnetics near the temperature of the orientational phase transition (OPT) is theoretically investigated. As the system stability is low near the OPT temperature, it facilitates the observation of the non-linear acoustic effects at moderate amplitudes. The non-linearity of the acoustic wave propagation is caused by the magnetostriction. The dissipation of the energy of the acoustic wave results in the increase of the temperature, and the decrease of the FMR frequency. It, in turn, leads to changes of the acoustic properties of the material, acoustic wave self-action.

Effect of acoustic oscillations on the stability of a plane jet

The problem of the effect of acoustic oscillations on the stability of a compressible ideal-fluid jet flow is examined in the case of a plane jet with standing acoustic waves superimposed across it. The method of dividing the motion into fast and slow with allowance for nonlinear acoustic effects is employed. The acoustic oscillations are found to affect the growth rate of unstable hydrodynamic disturbances.

Nonlinear acoustic phenomena due to bubble drift in a gas–liquid mixture

Nonlinear acoustic effects associated with collective dynamics of bubbles in a liquid are considered in this article. The mechanism of nonlinearity is caused by the variation of the bubble concentration in space due to bubble drift under the effect of radiation pressure and hydrodynamic (Bjerknes) forces (the latter may result in bubble coalescence). First, the individual behavior of a bubble or a pair of bubbles in an acoustic field is considered. Second, kinetic equations for the bubble distribution function in an acoustic field are derived, and, third, different effects of sound propagation are discussed. They include some steady-state and transient ‘‘envelope waves’’ propagating together with ‘‘concentration waves.’’ A simple model of ‘‘nonlinear transparency’’ in acoustics, which is in qualitative agreement with experimental results, is touched upon. A harmonic wave in a medium with homogeneous bubble distribution is shown to be unstable, and may possibly result in such effects as wave front conjugation, self-focusing of sound, and, probably, the formation of bubble groups.

Acoustic nonlinear effects in biological tissues and its application

Acoustic nonlinear effects in biological tissues and its application

Enhancements of acoustic levitation in the presence of increased gas pressure

Acoustic levitation for containerless materials processing has been investigated for use in the 1‐g environment. Enhancements have been obtained by increasing the gas pressure of the acoustic levitation system. Interdependence of gas pressure, sound pressure level, acoustic positioning force, and gas temperature has been measured. Also, nonlinear acoustic effects and harmonic content within the acoustic field are examined as a function of pressure. Finally, results of 1‐g acoustic levitation experiments utilizing increased gas pressures are presented. [Work supported by NASA.]

Seismic, acoustic, and ionospheric wave kinematics associated with moderate to large earthquakes

Unusually detailed Doppler radar records of ionospheric disturbances following two moderate‐to‐large dip‐slip earthquakes were reported in 1984. These indicate that earthquakes can perturb the ionosphere by means of acoustic waves launched by the moving ground surface. For one earthquake {magnitude 6.5, Coalinga, CA, 2 May 1983 [J. H. Wolcott et al., J. Geophys. Res. 89, 6835‐6839 (1984)]}, a seismic‐aeroacoustic‐ionospheric kinematic wave analysis was performed to explain radar signature timing. Surface Rayleigh waves were modeled and interpolated from main and after‐shock seismic records, acoustic wave trajectories by acoustic ray tracing in a standard atmosphere were established, and radar detection altitudes were determined from radio rays traced through an ionosphere calculated from an ionogram measured close by. Our calculated results agree well with Doppler signature times observed on several 5‐ and 10‐MHz radar beam paths 160–300 km from the epicenter. Similarities and differences were identified in the other earthquake {magnitude 7.1, Urakawa‐Oki, Japan, 21 March 1982 [T. Tanaka et al., J.Atm. Terr. Phys. 46, 233–245 (1984)]} and its signatures were studied to assess commonalities in perturbation mechanisms. It is tentatively proposed that nonlinear acoustic propagation effects could be significant in shaping observed Doppler signatures. [Work performed under the auspices of USDOE by LLNL under contract W‐7405‐Eng‐48.]

Direction finding circuit arrangement

A sonic energy scanning apparatus in which two directional primary sonic energy beams at two different frequencies are radiated into a medium capable of producing nonlinear acoustic effects to produce a third sonic energy beam having a given directional characteristic and a frequency equal to the difference between the frequencies of the primary beams. Scanning with the third beam is effected by varying the direction of the axes of, and the frequency difference between, the two primary beams in discrete steps for correspondingly varying the direction of the axis of the third beam over a selected angular sector and the frequency of the third beam such that each direction of the third beam axis is associated with a respectively different frequency, and by identifying the direction to a source of echoes of the third beam by determining the frequency of such echoes.

Observation of Nonlinear Acoustic Effects in a B-Scan Imaging Instrument

Observation of Nonlinear Acoustic Effects in a B-Scan Imaging Instrument

Comparison of procedures for determination of acoustic nonlinearity of some inhomogeneous materials

The widespread use of ultrasonic energy in medical diagnosis and therapy and the recent research showing the existence of nonlinear acoustic effects in inhomogeneous materials, like biological media, have led to a strongly increased interest in investigations aiming at providing enough information for an evaluation of the second order nonlinearity ratio B/A as a tissue characterizing parameter on a par with attenuation, impedance, etc. The several techniques used for the determination of B/A roughly fall into two main groups, finite‐amplitude methods and thermo‐dynamic‐acoustic methods. The B/A values determined using various techniques of the two main groups are strongly scattered, showing a dependence on the procedure used, which makes it difficult to draw any valid conclusions. The paper discusses advantages and disadvantages of the techniques used hitherto, aiming at an explanation of the reasons for the deviations between the present B/A results for biological media. The necessary accuracy in the determination and the reliability in the exploitation of B/A as a tissue characterizing parameter for clinical use are emphasized.

Nonsteady nonlinear acoustic effects in GA

Abstract Experimental data showing perhaps the development of turbulent processes in the electron subsystem in a metal by the propagation of the intensive sound signal are presented in this work.