Volume 112, Issue 5, November 2002
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
112(2002); http://dx.doi.org/10.1121/1.1510142View Description Hide Description
The predictions of two models of sound propagation in concentrated emulsions are compared with experimental measurements of ultrasonic velocity and attenuation in emulsions with volume fractions up to 0.7. The core-shell model includes irreversible heat transfer, viscoinertial forces, and multiple scattering [McClements et al., J. Acoust. Soc. Am. 105, 915–918 (1999)]. This model accounts for the effect of thermal interactions between neighboring particles by introducing an effective medium, and is valid for all volume fractions. The coupled phase model includes irreversible heat transfer and viscoinertial forces, and also is valid for all volume fractions, since it is derived from volume-averaged balance equations [J. M. Evans and K. Attenborough, J. Acoust. Soc. Am. 102, 278–282 (1997)]. This model has a significantly simpler formulation than the core-shell model and does not require the assumption of an effective medium. The coupled phase model is shown to be a good approximation to the core-shell model when the acoustic radius is small. Despite the fact that it does not include thermal interactions, the coupled phase model is shown to give at least as good agreement as the core-shell model with the experimental data, for all volume fractions, as long as the acoustic radius is less than 0.01.
112(2002); http://dx.doi.org/10.1121/1.1509427View Description Hide Description
Sonoluminescing single bubbles driven simultaneously by two harmonic frequencies were recently reported to increase the maximum light output up to a factor of 3 with respect to single mode excitation. In this paper, experimental and numerical results on single-bubble sonoluminescence (SBSL) in an air/water system using the fundamental mode of 25 kHz and the second harmonic at 50 kHz are presented. The region of light emission is mapped in the three-dimensional parameter space spanned by the two driving pressure amplitudes and their relative phase. Good agreement was seen between measured light output, maximum bubble radius, and stability boundaries and the numerical model which is based on spherical bubble oscillations regarding diffusive and shape stability. The maximum brightness was enhanced by a factor up to 2.5 with respect to single mode SBSL. However, long-term measurements reveal great variation of the emission at fundamental mode driven SBSL and of the boost factor reached with two frequencies. The overall brightness maxima of both excitation methods within a period of several hours turn out to show little difference.
The time-dependent magneto-visco-elastic behavior of a magnetostrictive fiber actuated viscoelastic polymer matrix composite112(2002); http://dx.doi.org/10.1121/1.1508790View Description Hide Description
The paper develops a one-dimensional magneto-elastic model of a magnetostrictive fiber actuated polymer matrix composite material which accounts for a strong viscoelastic response in the polymer matrix. The viscoelastic behavior of the compositepolymer matrix is modeled with a three parallel Maxwell element viscoelasticmodel, the magnetoelastic behavior of the composite fibers is modeled with an anhysteric directional potential based domain occupation theory. Example calculations are performed to identify and explain the dynamical behavior of the composite. These calculations assume that a constant stress and the oscillating magnetic field are applied in the fiber longitudinal direction. The inclusion of matrix viscosity results in an apparent hysteresis loop in the magnetization and magnetostriction curves even though the model does not include magnetoelastichysteresis in the fibers. The apparent hysteresis is a consequence of the interaction of the time varying fiber stress caused by matrix viscosity with a multidomain state in the fiber. The small increase in fiber longitudinal compressive stress due to matrix viscosity under increasing field inhibits the occupation of domains with magnetization orientations near the fiber longitudinal  direction. As a consequence, the summed longitudinal magnetization and magnetostriction is reduced as compared to the decreasing field limb.
112(2002); http://dx.doi.org/10.1121/1.1509424View Description Hide Description
The self-consistent model of Cherkaoui et al. [J. Eng. Mater. Technol. 116, 274–278 (1994)] is used to compute the effective materialmoduli of a viscoelastic material containing coated spherical inclusions. Losses are taken into account by introducing the frequency-dependent, complex shear modulus of the viscoelastic matrix. Mode conversion appears through the localization tensors that govern the micromechanical behavior near the inclusions. The results are compared with the scattering model and the data of Baird et al. [J. Acoust. Soc. Am. 105, 1527–1538 (1999)]. The two models are in good agreement. the advantage of the self-consistent model is that it is applicable to the case of nonspherical inclusions embedded in anisotropicmaterials.