Characterization of 1-3 Piezocomposite Using Lamb Waves Propagation

International audienceDue to their enhanced electromechanical properties with respect to conventional piezoelectric ceramics, 1-3 piezocomposite (1-3PC) materials are predominant in high performance ultrasonic array. Their complete effective electroelastic modulus (EEM) has a significant importance for numerical simulations to study undesired effects that almost depend on the transverse characteristics of the 1-3PC, such as mechanical cross-talks caused by Lamb waves. To determine the effective elastic, piezoelectric and dielectric tensors, theoretical homogenization models are available in literature. However, complete and accurate databases of each phase are required. In this work, a new method, based on direct measurements of propagative Lamb waves, is proposed to determine a complete 1-3PC EEM under operating conditions. First, in order to determine the 1-3PC EEM, experimental dispersion curves of the low-order Lamb waves are necessary. Then, experimental data are fitted using a recursive method that combines the theoretical curves obtained with Finite Element method and a fitting process based on a genetic algorithm. The cost function of this method intends to minimize the distance in the (w,k)-space between the three first symmetric and antisymmetric theoretical Lamb modes and those which were measured. A 1-3PC made of Pz27/Epoxy resin (70% volume fraction) with a pitch of 610�m was used to perform the measurements. Mass electrode covers the whole bottom surface while a thin rectangular electrode (15x1.11 mm<sup>2</sup>) was deposited on the top surface and aligned with the pillars of the 1-3PC to favor an particular propagation direction. Several electrode patterns were tested to change the propagation direction. Finally, a scanning laser vibrometer was used to measure normal displacements at the sample surface. Complete EEM was so obtained. These first results enable to demonstrate the efficiency and the robustness of this method for determining EEM experimentally. Other propagation directions were used to increase the solution?s accuracy