An Experimental Investigation of Subharmonic Generation in an Acoustic Interferometer

In our previous study [J. Acoust. Soc. Amer. 49, 119(A) (1971)], we showed that the nonlinear properties of the medium can induce coupling among the modes in a multiresonant system and the theory is able to predict the threshold and the steady-state response of subharmonic components. Such a mechanism is further illustrated by observing the subharmonic generation phenomenon in an acoustic interferometer. The experimental investigation was conducted with a 1.5-mHz driving signal and used filtered and degassed water as the medium. Data concerned with the actual modes of the interferometer, the loss factor associated with the subharmonic modes, and the threshold of subharmonic generation, with length of the interferometer and the driving frequency varying, are consistent with the analytic results provided that cavitation is carefully avoided. [The work was carried out at Harvard University and supported by the Office of Naval Research.]