Effect of shell thickness on sound propagation through encapsulated bubbles: A resonator approach

Abstract

The acoustics of elastic-shelled bubbles are of interest in applications ranging from biomedical imaging, to fisheries acoustics, to underwater noise abatement. Multiple models exist to predict the velocity and attenuation of sound propagating through water containing encapsulated bubbles, but existing measurements have yet been able to confidently verify model accuracy for void fractions above about 10−3. The effect of shell thickness was studied in this work using tethered, rubber-encapsulated bubbles bearing shells of varying thickness, deployed within a one-dimensional resonator apparatus. In previous work, resonator modes below the individual bubble resonance frequency (IBRF) were exploited to extract inferences of sound speed, but this is a regime where there is little difference between competing model prediction. In the present work, an increased understanding of the modal field inside the resonator has extended this technique to just below IBRF and to well above IBRF, both regimes where model behavior diversifies, thus providing a new opportunity for model verification. Measurement-model comparisons will be shown for encapsulated bubbles with radii ranging from 13 mm to 30 mm, void fractions ranging from 8.4×10−4 to 1.1×10−2, and shell thicknesses ranging from 0.085 to 0.16 mm. [Work supported by the Office of Naval Research.]