G.A.U.S., Dept. de genie mecanique, Univ. de Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada
In low frequency, the sound power radiated from planar structures is simply related to the net structural volume velocity. A cost function based on the volume velocity in active control of structural radiation has the advantage of keeping the control simple (one error sensor). The implementation of volume velocity error sensors in feedforward control of flexural beams and plates using shaped PVDF films is presented. For a beam, a single extended strip of prescribed shape is needed, while in the case of a panel, a number of shaped strips related to the number of flexural modes contributing to the volume velocity is required. The sensor obtained is independent of the type and frequency of excitation. A procedure for deriving the appropriate sensor shape, based on analytical or experimental modes, is discussed. The experimental implementation of volume velocity sensors is addressed and results of active control using piezoceramic (PZT) actuators are presented in the case of a simply supported beam, and simply supported or clamped panels. The strategy of minimizing the volume velocity is shown to provide significant acoustic attenuation for structural free-field radiation or transmission problems.