Frequencies of acoustically interacting bubbles

Work on the frequencies of mutual acoustic oscillation of finite numbers of bubbles is reviewed. In many applications in medicine, industry and nature, multiple bubbles create multiple modes of oscillation. We focus only on the linear modes established transiently on acoustic excitation. The self-consistent coupled-oscillator theory is adopted. Progressively larger numbers of bubbles are described, examining both the natural frequency, and the damping of the system. Even a single bubble has interesting behaviour when close to a wall: the wall creates a mirror image coupled to the real bubble. As more bubbles are introduced, the number of modes of mutual oscillation increases, permitting increasingly more complex behaviour. A large number of bubbles in a chain gives rise to a preferred direction for the propagation of sound, owing to the re-distribution of energy to bubbles along the chain. Finally, some applications of these phenomena are discussed