 |
George Kapodistrias defended his dissertation for a Ph.D. in mechanical engineering recently. First trained in aerospace engineering, his interest in acoustics brought him to APL-UW where he began work on acoustic scattering from assemblages of bubbles under Principal Engineer and Research Associate Professor Peter Dahl's direction. Bubbles, introduced to the sea surface by breaking waves or precipitation, can have dramatic effects on the behavior of underwater sound.
George was instrumental in helping Dahl set up APL-UW's Underwater Ultrasonics Laboratory. Here, he devised a method to hold bubbles less than 1 mm in diameter in water on a 150-µm-thick
|
|
waxed nylon thread. The technique allowed for controlled studies of multiple scattering problems of bubbles in water and verification of theoretical models. Experiments included the scattering response of two identical bubbles as a function of their proximity to each other and their relative position in the sound field, and the response of a single bubble close to an air-water interface. "This was the first experimental verification of a seminal result by Victor Twersky on interaction between two monopole scatters," notes Dahl. This knowledge is fundamental to understanding how acoustic signals scatter from oceanic bubble clouds, schools of fish, plankton, ultrasound contrast agents, and blood.
George is now a senior engineer at ATL Ultrasound-Philips Medical Systems in Bothell, Washington, working on new ultrasonic scanheads. Here he brings his experience in acoustics, signal processing, data analysis, and modeling to bear on his work in medical ultrasound. He continues to collaborate with Dahl and in a recently published paper, they present detailed modeling and experimental analysis of acoustic scattering from a bubble close to the water's surface. "These models can be easily modified to determine the scattering of more complex objects close to the surface of the water, or incorporate roughened surfaces," notes George.
|
|
