Index of content:
Volume 106, Issue 1, July 1999
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
106(1999); http://dx.doi.org/10.1121/1.427048View Description Hide Description
This paper describes the interaction between cavities in transient multibubble cavitation which is due to the pressurewaves emitted by collapsing bubbles. These waves sum up to a time-dependent “secondary pressure” which accelerates the collapse of contracting bubbles. Since, in each cycle of the exciting sound field the smallest bubbles are the first to implode, this interaction results in an energy transfer from smaller bubbles to larger ones, which undergo particularly violent collapses. This effect is demonstrated by a few examples.
106(1999); http://dx.doi.org/10.1121/1.427073View Description Hide Description
A one-dimensional model is developed to predict the acoustic waves generated in viscoelastic rods by electromagnetic microwave pulses. The wave generation is due to the rapid thermal expansion caused by microwaveabsorption. The distribution of the temperature rise along the rod is taken to be either uniform or linear. The effects of this distribution and of the microwave pulsewidth are investigated numerically. Some tests are carried out on PVC rods instrumented with accelerometers. The presence of the accelerometer mass at the end of the rod is taken into account in the model. The comparison between the experimental and the theoretical accelerations leads to the evaluation of the maximum temperature rise during one pulse. Although this temperature rise is found to be extremely low, it produces acoustic waves easily detectable with the accelerometer. The inverse problem to estimate the viscoelastic properties of the rod and the temperature rise is approached by means of a numerical minimization technique.