A Study of the Broadband Parametric Acoustic Array

摘要

The characteristics of the broadband parametric acoustic array are studied both theoretically and experimentally as a function of primary frequency directivity. The broadband parametric array describes the sound field produced by the nonlinear interaction of the frequency components of a pulsed primary signal. In the present investigation, the secondary sound field of the baseband modulation products is considered. The primary transmissions are produced by physically realizable sources, and the broadband parametric array for nonplane wave fields is developed. A general solution for the parametric array for nonplane wave fields is presented in the form of the superposition of primary field components. An experimental study of the broadband parametric array is presented which provides data with variations in experimental parameters and an emphasis on the behavior as a function of primary directivity. The results for low amplitude primary signals generally confirm the theoretical predictions. An extreme sensitivity to the sidelobe structure in the primary off-axis transfer function is noted in the frequency at the spectral peak of the secondary power spectra. No such sensitivity was noted in the level at the spectral peak or in the secondary power beam pattern. For high amplitude primary signals, the results indicate that envelope distortion due to finite amplitude effects in the primary signal causes spectral distortion in the secondary signals. The spectral distortion is greatest on-axis where the frequency at the spectral peak is reduced. Far off-axis, the characteristics are the same as those for low amplitude primary transmissions.