Low-Frequency Resonant Scattering of Bubble Clouds*

Abstract

Abstract The acoustic properties of water can be drastically modified by a small amount of air content in the fluid. The dynamics of bubble clouds and their collected oscillation mechanisms are among topics of active research in underwater acoustics. In the ocean, bubble clouds are long lasting, and most of the time can be considered as passive scatterers. Solutions of the key parameters such as resonance frequencies, sound speed, and target strength can be derived from treating the bubble cloud as a homogeneous medium with proper effective bulk properties. In this paper, the resonance frequency and target strength are derived from computations based on a classical solution for acoustic scattering of elastic spheres. The range of void fractions covers four orders of magnitude and includes single air bubbles as its asymptotic condition of void fraction equals unity. Based on these computations, it is found that the isothermal condition is approached only at very low void fraction levels (<10−4). At high vo...