Description:
<jats:p>It has been reported [J. Acoust. Soc. Amer. 46, 94(A) (1969)] that the observed fractional harmonics in a liquid-filled resonant ultrasonic cavity are parametrically excited ultrasonic waves. This excitation is produced by instabilities introduced through the vibration of the driver transducer that forms one end of the cavity. The theoretically derived threshold criterion that defines the range of amplitudes for such excitation is now tested experimentally. Since the theory predicts that the transducer voltage at threshold is a function of the driver frequency, the absorption per wavelength of the medium, and the cavity length, a change in either of these parameters causes a corresponding change in the transducer voltage at threshold. There is reasonable agreement between theory and experiment. To develop the model further, a nonlinear equation of parametric action is derived. The solution of the equation including the first nonlinear terms confirms the experimental observation that the nonlinearity of the medium does not affect the magnitude of the threshold for parametric oscillation. [Research sponsored by the U. S. Office of Naval Research.]</jats:p>