Control of Sound Radiation with Adaptive Structures

Active control of sound radiation from a vibrating simply supported rec tangular plate excited by a steady state harmonic point force disturbance is experimentally studied. A variety of test cases were studied for controlling sound radiation due to a distur bance both on and off structural resonance. Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the plate. The control approach is based upon a Filtered-X version of the adaptive LMS algorithm. Error information for the con troller was taken from two sensor formats, either microphones placed in the acoustic far- field, or polyvmylidene fluoride (PVDF) piezoelectric distributed sensors bonded to the surface of the structure. The two narrow strip PVDF sensors were positioned on the plate such that the dominant observed response was due to the odd-odd and to a lesser degree, the odd-even modes (i.e., the more efficient acoustic radiators). Results from these experi ments indicate that piezoceramic elements provide an efficient method for modification of structural response to attenuate sound radiation. In many cases, the PVDF sensors were as effective as microphones in providing error information necessary to reduce the far-field sound radiation from the structure. In addition, the adaptive LMS algorithm is shown to be an effective narrowband controller, which in contrast to feedback approaches, requires no exact system modelling.