The Effect of Shape, Shell Thickness, and Fill Material on the Resonance Frequency, Quality Factor and Attenuation of Bubbles

date November 15, 2013
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Friday, November 15, 2013 4:00 p.m. in ETC 4.150

Kyle S. Spratt and Gregory R. Enenstein
Applied Research Laboratories and Mechanical Engineering Department
The University of Texas at Austin

The topics discussed are related to the acoustics of air bubbles in water, with applications in underwater noise abatement and the acoustics of fish schools.  The first half of this seminar describes an investigation of the resonance frequency of an arbitrarily shaped ideal bubble using an analytical, lumped-element approach.  The problem of finding the effective mass of the bubble is equivalent to a classical problem in electrostatics, as was first noted by M. Strasberg in 1953 [J. Acoust. Soc. Am. 25, 536–537].  The resonance frequency for various bubble geometries is presented, with special attention paid to the case of a toroidal bubble, and the results are compared with a finite-element numerical model of the corresponding full acoustic scattering problem.  The second half of the seminar explores some details of encapsulated bubble acoustics (shell thickness and fill material) and also describes a simple laboratory measurement technique that is being developed to substitute for expensive open-water tests.  Measurements made in a small (sub-wavelength) laboratory tank of the resonance frequencies and quality factors of single encapsulated bubbles with various shell thicknesses and fill materials are compared to measurements of the attenuation due to arrays of the same encapsulated bubbles measured in open water.