Broadband acoustic scattering from a bubbly liquid-filled compliant cylinder with known bubble population statistics

Abstract

In previous experiments, acoustic scattering from a bubbly liquid-filled latex tube was investigated in the 5–20 kHz frequency range. The mean bubble resonance frequency was 113 kHz, and a Wood limit effective medium theory was found to quantitatively describe the scattering throughout the measurement range, using a void fraction as the model’s only fit parameter [Wilson et al., Acoust. Res. Lett. Online (in press)]. New measurements will be presented that extend the frequency range to 150 kHz and include in-situ void fraction measurement. A preliminary analysis of the new data shows qualitative agreement with the effective medium theory up to about 35–40 kHz. Above this range, the qualitative trends predicted by the model are no longer apparent, and an increased ping-to-ping variability in the received echo is observed. As the frequency approaches individual bubble resonance frequency, one proceeds from a continuum response where the bubble distribution is not important to a region where individual bubbles and groups of bubbles play a role. Moreover, as the frequency goes up, losses in the latex rubber tube wall should become increasingly important. An analysis of the data, which includes bubble resonance effects and tube wall losses, will be presented. [Work supported by ONR.]