My current work involves two seemingly unrelated topics in physical acoustics: bubbles in sediments and nonlinear wave propagation.

I am interested in the resonance response of a gas bubble trapped in a saturated sediment. A gas bubble in water has an enormous scattering cross section near and at its monopole resonance frequency (due principally to the compressibility of the gas). Under sediment loading, one expects the scattering cross section to be reduced through various attenuation mechanisms. However, a curious property of a (consolidate) saturated porous medium is its ability to support two distinct longitudinal waves of propagation. Hence, a gas bubble in a sediment can, in theory, have two monopole resonance frequencies. I am investigating whether this hypothesis is correct.

Nonlinear wave propagation in a fluid inherently effects the supporting medium. A simple example is energy dissipation through absorption by the fluid, and hence, a local increase in the temperature. Of course, the linear sound speed is temperature. I am interested in the effects of nonlinear wave propagation (in an ocean environment) on beam forming. Beam forming is the ability to use an array of transducers (or ceramic elements) to produce a steerable bounded beam. Under linear wave propagation, the characteristics of the beam are determined by the principle of superposition as well as physical properties of the array. When the drive amplitude to the array is increased, and nonlinear effects start to become important, linear superposition may (should) break down. Hence, the possibility of beam forming under nonlinear wave propagation conditions becomes an important question to address.

Although these topics appear to be unrelated, the presence of bubbles in a fluid medium significantly increases its nonlinear behavior. Thus, the common link between my current areas of research is the dynamical behavior of bubbles in both linear and nonlinear systems.

Back to Kargl's home page

990420