Autophasing of free volume oscillations of air cavities in water

This paper deals with theoretical and experimental investigations on free oscillations of air cavities formed in a metal plate lying on a water surface. The cavity is both an oscillator produced by the air elasticity in combination with the water mass, and a source of sound. Unlike gas bubbles in water, a cavity allows one to control the cubic nonlinearity coefficient up to a change of sign and to excite free oscillations rather easily. Measurements of the eigenfrequencies, damping factor, and the cubic nonlinearity coefficient of oscillations, taken for a variety of cavity volumes, are reported. Two-and three-cavity systems have been investigated to determine the eigenfrequencies of oscillations of the monopole and dipole modes. For the first time, the effect of autophasing of oscillations generated by ensembles of two and of three oscillators involved in a linear interaction via the near field was observed. The energy of the dipole oscillations of the system was transferred in this process to the monopole oscillations that effectively radiated acoustic waves. A possibility is discussed of using such oscillators as active elements for acoustic masers. (C) 1998 Acoustical Society of America.