This technique was implemented in the framework of the DAFNOR project (EC funded Brite-Euram project Distributed Active Foils for NOise Reduction), that demonstrated the feasibility of using piezoelectric foils for active noise control. The ASAC (Active Structural Acoustic Control) panel, developed and built for this project exhibits a colocated quadratically shaped piezoelectric actuator/sensor pair. This paper stresses the influence of the membrane components on the modelling of such control systems.

The transfer functions between the inputs and the outputs of a control system involving embedded distributed piezoelectric actuators and sensors in a shell structure are not easy to determine numerically. The situation where they are nearly collocated is particularly critical, because the zeros of the transfer functions are dominated by local effects which can only be accounted for by finite elements.

In a first section, The theory of piezolaminated plates is presented, starting from the linear piezoelectric constitutive equations and the classical theory of plates.

In a second section, the fundamental equations governing the equivalent piezoelectric loads and sensor output are derived from the piezolaminated plate equations. The reciprocity between piezoactuation and piezosensing is pointed out.

In a third section, the finite element formulation for an electro-mechanically coupled piezoelectric problem is sketched. The transfer functions between actuators and sensors are obtained using a state space model of the control system extracted from the dynamic finite element analysis. The importance of the in-plane component is illustrated by a cantilever plate with four nearly collocated piezoceramic patches. The transfer functions obtained experimentally are compared with numerical finite element results using different hypothesis.

In the final section, acoustic control using shaped piezotransducers is presented. The (DAFNOR-ASAC) panel for active noise control using a colocated actuator/sensor pair is described. An analytical model is presented and compared with transfer functions obtained experimentally and using a multilayer piezoelectric finite shell element model. The influence of the in-plane components on the open-loop transfer functions of this collocated vibroacoustic control system is discussed.

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