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Jun 2012

Volume 131, Issue 6, pp. EL421-4870

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Linear and nonlinear Biot waves in a noncohesive granular medium slab: Transfer function, self-action, second harmonic generation

J-B. Legland, V. Tournat, O. Dazel, A. Novak, and V. Gusev

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4292-4303 (2012); (12 pages)

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Experimental results are reported on second harmonic generation and self-action in a noncohesive granular medium supporting wave energy propagation both in the solid frame and in the saturating fluid. The acoustic transfer function of the probed granular slab can be separated into two main frequency regions: a low frequency region where the wave propagation is controlled by the solid skeleton elastic properties, and a higher frequency region where the behavior is dominantly due to the air saturating the beads. Experimental results agree well with a recently developed nonlinear Biot wave model applied to granular media. The linear transfer function, second harmonic generation, and self-action effect are studied as a function of bead diameter, compaction step, excitation amplitude, and frequency. This parametric study allows one to isolate different propagation regimes involving a range of described and interpreted linear and nonlinear processes that are encountered in granular media experiments. In particular, a theoretical interpretation is proposed for the observed strong self-action effect.
Show PACS
43.25.Dc Nonlinear acoustics of solids
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics

Nonequilibrium phenomena in damaged media and their effects on the elastic properties

M. Scalerandi, A. S. Gliozzi, C. L. E. Bruno, and P. Antonaci

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4304-4315 (2012); (12 pages) | Cited 2 times

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Concrete, particularly if damaged, exhibits a peculiar nonlinear elastic behavior, which is mainly due to the coupling between nonequilibrium and nonlinear features, the two of which are intrinsically connected. More specifically, the formulation of a constitutive equation able to properly predict the dynamic behavior of damaged concrete is made difficult by the concomitant presence of two mechanisms: The modification of the microstructure of the medium and the transition to a new elastic state caused by a finite amplitude excitation (conditioning). Memory of that new state is kept when the excitation is removed, before relaxation back to the original elastic state takes place. Indeed, besides accounting for linear and nonlinear parameters, a realistic constitutive equation to be used in reliable prediction models should take into account nonequilibrium effects. Specific parameters, sensitive to finite amplitude excitations, should be introduced to provide information about conditioning effects. In this paper, experimental results indicating that nonlinearity of damaged concrete is memory-dependent will be presented and the implications of such findings in the development of physical models, with relevant outcomes for the characterization of hysteretical features, will be discussed.
Show PACS
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Dc Nonlinear acoustics of solids
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.35.Yb Ultrasonic instrumentation and measurement techniques

Nonlinear elastic imaging using reciprocal time reversal and third order symmetry analysis

Francesco Ciampa and Michele Meo

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4316-4323 (2012); (8 pages) | Cited 1 time

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This paper presents a nonlinear imaging method for the detection of the nonlinear signature due to impact damage in complex anisotropic solids with diffuse field conditions. The proposed technique, based on a combination of an inverse filtering approach with phase symmetry analysis and frequency modulated excitation signals, is applied to a number of waveforms containing the nonlinear impulse responses of the medium. Phase symmetry analysis was used to characterize the third order nonlinearity of the structure by exploiting its invariant properties with the phase angle of the input waveforms. Then, a “virtual” reciprocal time reversal imaging process, using only one broadcasting transducer and one receiving transducer, was used to insonify the defect taking advantage of multiple linear scattering as mode conversion and boundary reflections. The robustness of this technique was experimentally demonstrated on a damaged sandwich panel, and the nonlinear source, induced by low-velocity impact loading, was retrieved with a high level of accuracy. Its minimal processing requirements make this method a valid alternative to the traditional nonlinear elastic wave spectroscopy techniques for materials showing either classical or non-classical nonlinear behavior.
Show PACS
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.40.Fz Acoustic scattering by elastic structures
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission

Modeling nonlinear ultrasound propagation in heterogeneous media with power law absorption using a k-space pseudospectral method

Bradley E. Treeby, Jiri Jaros, Alistair P. Rendell, and B. T. Cox

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4324-4336 (2012); (13 pages) | Cited 3 times

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The simulation of nonlinear ultrasound propagation through tissue realistic media has a wide range of practical applications. However, this is a computationally difficult problem due to the large size of the computational domain compared to the acoustic wavelength. Here, the k-space pseudospectral method is used to reduce the number of grid points required per wavelength for accurate simulations. The model is based on coupled first-order acoustic equations valid for nonlinear wave propagation in heterogeneous media with power law absorption. These are derived from the equations of fluid mechanics and include a pressure-density relation that incorporates the effects of nonlinearity, power law absorption, and medium heterogeneities. The additional terms accounting for convective nonlinearity and power law absorption are expressed as spatial gradients making them efficient to numerically encode. The governing equations are then discretized using a k-space pseudospectral technique in which the spatial gradients are computed using the Fourier-collocation method. This increases the accuracy of the gradient calculation and thus relaxes the requirement for dense computational grids compared to conventional finite difference methods. The accuracy and utility of the developed model is demonstrated via several numerical experiments, including the 3D simulation of the beam pattern from a clinical ultrasound probe.
Show PACS
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.20.Bi Mathematical theory of wave propagation
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Acoustic radiation force of a Bessel beam on a porous sphere

Mahdi Azarpeyvand

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4337-4348 (2012); (12 pages) | Cited 1 time

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The possibility of using acoustic Bessel beams to produce an axial pulling force on porous particles is examined in an exact manner. The mathematical model utilizes the appropriate partial-wave expansion method in spherical coordinates, while Biot’s model is used to describe the wave motion within the poroelastic medium. Of particular interest here is to examine the feasibility of using Bessel beams for (a) acoustic manipulation of fine porous particles and (b) suppression of particle resonances. To verify the viability of the technique, the radiation force and scattering form-function are calculated for aluminum and silica foams at various porosities. Inspection of the results has shown that acoustic manipulation of low porosity (<0.3) spheres is similar to that of solid elastic spheres, but this behavior significantly changes at higher porosities. Results have also shown a strong correlation between the backscattered form-function and the regions of negative radiation force. It has also been observed that the high-order resonances of the particle can be effectively suppressed by choosing the beam conical angle such that the acoustic contribution from that particular mode vanishes. This investigation may be helpful in the development of acoustic tweezers for manipulation of micro-porous drug delivery carrier and contrast agents.
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43.25.Qp Radiation pressure
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.40.Fz Acoustic scattering by elastic structures
43.25.Uv Acoustic levitation

Modeling non-spherical oscillations and stability of acoustically driven shelled microbubbles

Jonathan Loughran, Robert J. Eckersley, and Meng-Xing Tang

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4349-4357 (2012); (9 pages)

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The oscillation and destruction of microbubbles under ultrasound excitation form the basis of contrast enhanced ultrasound imaging and microbubble assisted drug and gene delivery. A typical microbubble has a size of a few micrometers and consists of a gas core encapsulated by a shell. These bubbles can be driven into surface mode oscillations, which not only contribute to the measured acoustic signal but can lead to bubble destruction. Existing models of surface model oscillations have not considered the effects of a bubble shell. In this study a model was developed to study the surface mode oscillations in shelled bubbles. The effects of shell viscosity and elasticity on the surface mode oscillations were modeled using a Boussinesq–Scriven approach. Simulation was conducted using the model with various bubble sizes and driving acoustic pressures. The occurrence of surface modes and the number of ultrasound cycles needed for the occurrence were calculated. The simulation results show a significant difference between shelled bubbles and shell free bubbles. The shelled bubbles have reduced surface mode amplitudes and a narrower bubble size range within which these modes develop compared to shell free bubbles. The clinical implications were also discussed.
Show PACS
43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Ei Acoustic cavitation in liquids

Ambient pressure dependence of the ultra-harmonic response from contrast microbubbles

Tao Sun, Nan Jia, Dong Zhang, and Di Xu

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4358-4364 (2012); (7 pages) | Cited 1 time

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Sub-harmonic response from ultrasound contrast agent microbubbles has been demonstrated to be an effective modality for noninvasive pressure measurement. In the present study, the dependence of ultra-harmonic response on the ambient overpressure was investigated by both experimental measurements and simulations. In the measurements, the microbubbles were exposed to Gaussian pulses with varied driving frequencies and pulse lengths, at an acoustic pressure of 0.3 MPa. The amplitudes of sub- and ultra-harmonic components were measured when the ambient overpressures varied from 0–25 kPa. At the driving frequency of 1.33 MHz, the ultra-harmonic energy decreased but the sub-harmonic energy increased with the increasing overpressure; while at the driving frequency of 4 MHz, both the sub- and ultra-harmonic components showed the same tendency that the corresponding energy decreased as the overpressure was increased. A 4-MHz Gaussian pulse with 64 cycles could provide an ultra-harmonic response with both good ambient pressure sensitivity and high linearity. Furthermore, the effects of shell parameters of a microbubble on the generation of ultra- and sub-harmonic responses were discussed based on simulations using Marmottant’s model. This study suggests that the ultra-harmonic response from contrast microbubbles might be applicable for noninvasive pressure measurement.
Show PACS
43.25.Yw Nonlinear acoustics of bubbly liquids
43.80.Qf Medical diagnosis with acoustics

Fast simulation of second harmonic ultrasound field using a quasi-linear method

Fabrice Prieur, Tonni Franke Johansen, Sverre Holm, and Hans Torp

J. Acoust. Soc. Am. Volume 131, Issue 6, pp. 4365-4375 (2012); (11 pages) | Cited 1 time

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Nonlinear propagation of sound has been exploited in the last 15 years in medical ultrasound imaging through tissue harmonic imaging (THI). THI creates an image by filtering the received ultrasound echo around the second harmonic frequency band. This technique produces images of enhanced quality due to reduced body wall reverberation, lower perturbations from off-axis echoes, and multiple scattering of reduced amplitude. In order to optimize the image quality it is essential to be able to predict the amplitude level and spatial distribution of the propagating ultrasound pulse. A method based on the quasi-linear approximation has been developed to quickly provide an estimate of the ultrasound pulse. This method does not need to propagate the pulse stepwise from the source plane to the desired depth; it directly computes a transverse profile at any depth from the definitions of the transducer and the pulse. The computation handles three spatial dimensions which allows for any transducer geometry. A comparison of pulse forms, transverse profiles, as well as axial profiles obtained by this method and state-of-the-art simulators, the KZKTexas code, and Abersim, shows a satisfactory match. The computation time for the quasi-linear method is also smaller than the time required by the other methods.
Show PACS
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.80.Vj Acoustical medical instrumentation and measurement techniques
43.60.Uv Model-based signal processing
43.60.Gk Space-time signal processing, other than matched field processing
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