This thesis studies the reduction of radiated and transmitted sound power by means of piezoelectric passive networks. A detailed analysis of the radiation and transmission properties of thin plates is presented, and this concept are used for the optimization of the smart structures. Two main control strategies are considered: localized and distributed control. In localized control the piezoelectric elements are positioned in selected ocations, and the circuit is optimized for concentrating the effort of control in the reduction the radiated sound power. The modelling, optimization and experimental implementation of a localized smart plate is presented. In distributed control the transducers are uniformly disposed on the structure, exploiting this spatial distribution for controlling the radiation. The modelling of an innovative structure, the Piezoelectric Resistive Electrode plate, is described in details
