AUTOPHASING OF FREE-VOLUME OSCILLATIONS OF AIR CAVITIES IN WATER

This paper deals with theoretical and experimental investigations on f ree oscillations of air cavities formed in a metal plate lying on a wa ter surface. The cavity is both an oscillator produced by the air elas ticity in combination with the water mass, and a source of sound. Unli ke gas bubbles in water, a cavity allows one to control the cubic nonl inearity coefficient up to a change of sign and to excite free oscilla tions rather easily. Measurements of the eigenfrequencies, damping fac tor, and the cubic nonlinearity coefficient of oscillations, taken for a variety of cavity volumes, are reported. Two-and three-cavity syste ms have been investigated to determine the eigenfrequencies of oscilla tions of the monopole and dipole modes. For the first time, the effect of autophasing of oscillations generated by ensembles of two and of t hree oscillators involved in a linear interaction via the near field w as observed. The energy of the dipole oscillations of the system was t ransferred in this process to the monopole oscillations that effective ly radiated acoustic waves. A possibility is discussed of using such o scillators as active elements for acoustic masers. (C) 1998 Acoustical Society of America.