Volume 103, Issue 6, June 1998
Index of content:
- NONLINEAR ACOUSTICS, MACROSONICS 
103(1998); http://dx.doi.org/10.1121/1.423075View Description Hide Description
Propagation resulting from finite pulselength stresses applied at one end of a hysteretic material is analyzed using a propagation model containing a double modulus, or two-signal-speed, approximation of the stress-strain relation. The local signal speed is determined at any instant by both the value of stress and the sign of its time derivative (i.e., time-local history). It is shown that far-field waveforms do not determine unique source profiles. The propagation mechanism responsible for the ambiguity in source identification is common to broad classes of both local and global hysteretic stress-strain operators. Consequently, one may expect that it is typical of hysteretic materials that remote sources are not uniquely determined by observed waveforms.
New evolution equations for the nonlinear surface acoustic waves on an elastic solid of general anisotropy103(1998); http://dx.doi.org/10.1121/1.423036View Description Hide Description
New evolution equations for the nonlinear surface acoustic waves in anisotropic media are derived in the frame of the second-order elasticity theory. The proposed theory explicitly accounts for the possible significant difference of the depth structure of the nonlinear surface acoustic waves with the depth structure of the linear surface acoustic waves. The derived equations reduce to the form, recently obtained for the nonlinear Rayleigh surface acoustic waves in isotropic solids, when two partial waves (contributing to the surface acoustic wave propagating along a crystal axis in the basal plane of a cubic crystal) exhibit purely exponential decay in depth.
Dispersion of nonlinearity, nonlinear dispersion, and absorption of sound in micro-inhomogeneous materials103(1998); http://dx.doi.org/10.1121/1.423037View Description Hide Description
New evolution equations for nonlinear acousticwaves in micro-inhomogeneous media, which take into account relaxation processes, are derived. The proposed theory provides the description of such physical effects as frequency-dependent nonlinear absorption of sound, nonlinearity of its velocity dispersion, and dispersion of the nonlinear acoustic parameters of micro-inhomogeneous materials. The theory predicts that, depending on the ratio of the characteristic relaxation time to the wave period, nonlinearity can grow or diminish with increasing frequency, while an increase in wave amplitude can lead to a rise or fall of the propagation velocity. In the limiting cases where the relaxation processes are instantaneous or quasi-frozen, analytical solutions of the nonlinear equations are found and analyzed.
Experimental detection of a subharmonic route to chaos in acoustic cavitation through the tuning of a piezoelectric cavity103(1998); http://dx.doi.org/10.1121/1.423038View Description Hide Description
Experimental observation is reported of a subharmonic route to chaos through the tuning of a piezoelectriccavity. The emission spectrum of bubbles generated in a liquid contained in the cavity through the application of a pressureultrasonic field of constant frequency is analyzed. The cavity height is used as control parameter to vary the resonance frequency of the cavity. In the emission spectrum of the bubbles subharmonics of the excitation frequency are observed. This phenomenon is identified as a period-doubling bifurcation and is explained on the basis of a simple model of resonance in the cavity. The appearance of subharmonics is highly sensitive to changes in the cavity height.
103(1998); http://dx.doi.org/10.1121/1.423039View Description Hide Description
Near-field acoustic levitation is successfully applied to transport objects without contact. Planar objects having a weight greater than 10 kgf can be stably levitated near a vibrating plate. An experimental apparatus has been fabricated to measure the transportation speed and transient characteristics.