ACTIVE NOISE-CONTROL BY MINIMIZATION OF V OLUME VELOCITY OF STRUCTURES - ANALYTIC AND EXPERIMENTAL RESULTS

The active control of structurally radiated sound requires in general a large number of error sensors on the vibrating structure. A simple c ontrol strategy, using only one error signal -the volume velocity of t he structure- has recently been proposed. Such a strategy allows (i) t o control all the structural modes that are monopole radiators at low frequencies (i.e., with a high radiation efficiency), (ii) to keep the control set-up simple (only one information is to be minimized). The volume velocity is measured using piezoelectric PVDF strip. The shape of the PVDF strip is determined in such a way that the output signal f rom the PVDF sensor is directly proportional to the volume velocity in duced by the structure on which it is bonded. Using a modal approach, the sensor shape is shown to depend only on the structure and sensor c haracteristics. However, it is independent of the excitation and the f requency. For a simply supported beam, the shape of such a PVDF sensor is shown and experimental validations are presented for the measure o f the volume velocity. Active control was then implemented with this P VDF error sensor and piezoceramic actuators for different frequencies of excitation, using a one-channel feedforward adaptive LMS algorithm. Results show that sound radiation can be efficiently attenuated using this strategy when the system is driven ''on-resonance''. However, wh en the system is driven ''off-resonance'', the axial effects induced b y the asymmetric piezoceramic actuators limit the control efficiency.