The acoustic bubble: Oceanic bubble acoustics and ultrasonic cleaning

Bubbles interact strongly with sound fields. Gas bubbles in the ocean generate sound as they are produced by breaking waves, rainfall, methane seeps, etc., and such emissions can be used to size and count the bubbles present. However after production, when the pulsations of such bubbles have damped away, they are silent unless re-excited. These, and other bubbles in the ocean that do not generally make significant passive sound emissions (such as those that appear through exsolution, and a range of biological processes including decomposition, photosynthesis, respiration and digestion) can still strongly influence applied sound fields through scattering, and changing the sound speed and absorption from that which would be expected in bubble-free water. This paper discusses how these phenomena might be associated with bubble netting by cetaceans. When driven with appropriate acoustic fields, bubbles can change their surrounding environment, and examples of this are shown through the generation of cleaning in an ultrasonically-activated stream of cold water, without additives.