Abstract:

A change of the resonant frequency of an acoustic chamber can arise due to the presence and migration of objects inside the chamber. In the investigations of collinear four-wave mixing mediated by a suspension, it was noticed that for sufficiently high particle concentrations, the resonant frequency of the chamber shifted as the particles formed periodically spaced bands, due to the induced radiation pressure from two counter-propagating pump waves. This frequency shift, which also affects the Q factor of the cavity, is another manifestation of the interaction of sound with sound. A transfer-matrix approach was developed which uses a continuum approximation for the particle suspension, and is in good agreement with previous theory and experiment. By using sufficiently gassy water, pump pressures of large enough amplitude led to the measurement of the response of the system to cavitation bubbles. By proper tuning, the frequency shift of higher azimuthal modes of the cylindrical cavity were probed, with experimental results showing both stable and unstable modes. [Work was supported by the Office of Naval Research.]