Volume 116, Issue 4, October 2004
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
116(2004); http://dx.doi.org/10.1121/1.1785631View Description Hide Description
Controlling and/or monitoring the degree of mixing between constituents of a multicomponent media is a key problem in a variety of applications. Monitoring such mixing processes necessarily requires capabilities for quantification of the level of “mixedness.” However, quantification of molecular mixedness levels, as opposed to macroscale mixture uniformity, is difficult. This paper demonstrates the use of acoustic absorptionmeasurements to characterize an average level of molecular mixedness between gases across the wave propagation path. This approach takes advantage of the fact that over a large frequency range, acoustic damping is dominated by vibrational relaxation processes. The vibrational relaxation frequency for a particular gas is often a strong function of the other species it is in molecular contact with. Thus, the relaxation frequency of each species in a multicomponent gas mixture varies with the level of molecular mixedness of the constituent species. This paper presents the results of example calculations and experiments demonstrating the feasibility of this approach and the significant sensitivity of acoustic absorption levels upon gas mixedness; e.g., measurements reported here show acoustic amplitude differences of up to a factor of 10 between identical gas mixtures whose only difference is the level of mixedness of their constituents.
116(2004); http://dx.doi.org/10.1121/1.1784435View Description Hide Description
A theoretical study of Lamb mode propagation through a part of a plate containing a finite-length, delamination parallel with the surface is presented. In the delamination boundary region, which is taken parallel with the free plate surface, noncontact boundary conditions are assumed. The calculation is based on a modal decomposition method. As a result of diffraction on a delamination the incident Lamb mode is efficiently converted into Lamb modes with wave numbers close to the wave number of incident mode. The transmission coefficient of a Rayleigh wave incident on a delamination located near the surface has an oscillating dependence on the delamination parameters and has a pronounced minimum where there is a strong conversion into transmitted Lamb modes. Inversely, using the method of phase conjugation, a proper incident Lamb mode combination can be efficiently converted into a single transmitted Lamb or Rayleigh wave.
116(2004); http://dx.doi.org/10.1121/1.1791718View Description Hide Description
The analysis of acoustic waves generated by a transient normal point load applied on a fluid–solid interface is presented. The closed-form exact solution of the wave motion is obtained by using integral transform techniques. The obtained analytical solution provides necessary theoretical background for optimization of fluid-coupled ultrasonic and acoustic wavedetection in experiments. Numerical simulation (elastodynamic finite integration technique) is performed to verify the obtained analytical solution. Detailed descriptions of leaky Rayleigh and Scholte wavesolutions are presented. A simplified solution to isolate the contributions of leaky Rayleigh and Scholte waves generated by a transient point load is proposed, and closed-form formulations for displacement and stress components are then presented. The simplified solution is compared to the exact solution for two configurations: water/concrete and air/concrete. The excitation effectiveness of leaky Rayleigh waves for the air/concrete configuration is studied, which has practical significance to air-coupled sensing in civil engineering structures.