Active control of sound radiation using volume velocity cancellation

Abstract

The active control of sound transmission through a panel has been formulated using a near-field approach. The effects of minimizing the sound power radiated by the panel and of canceling the net volume velocity of the panel are compared not only in terms of the reduction in sound radiation but also in terms of the change in the space average mean-squared velocity of the panel and the space average mean-squared pressure at its surface. Simulations of a thin panel excited by an incident acoustic plane wave and a piezoelectric control actuator show that volume velocity cancellation gives similar reductions in the transmitted sound power to the minimization of sound power radiation up to frequencies at which the size of the plate is about half an acoustic wavelength. The acoustic radiation is analyzed in terms of the radiation modes of the panel which are also used to explain spillover effects. Spillover, which leads to increases in the mean-squared velocity of the panel and to increases in near-field pressure levels when using a piezoelectric patch as a secondary actuator can be removed by using an actuator which generates a uniform force over the surface of the panel. Such an actuator is the reciprocal of the volume velocity sensor and could be fabricated in the same way. The transfer function between such a matched actuator/sensor pair is shown to be minimum phase, so that the performance of a feedback control system should be as good as a feedforward one, which would allow control of arbitrary broadband excitation of the panel.