Comparison of different piezoelectric materials for the design of embedded transducers for structural health monitoring applications

This paper describes the design requirements for embedded piezoelectric plate transducers suitable for generating efficient, uni-modal Lamb wave signals in plate structures. Three piezoelectric materials are considered, modified lead titanate, lead zirconate titanate, and polyvinylidene difluoride, in conjunction with different 1-3 piezoelectric composite configurations. Finite element modelling was used to predict the various Lamb wave modes generated by transducers embedded in a hard-set epoxy plate. Accordingly, the design requirements for successful generation of the zeroth order symmetric (So) Lamb wave mode have been identified. It is shown that the transducer position and the orientation within the host structure, and the appropriate choice of the excitation frequency of the Lamb wave, relative to the structural resonances, are the crucial design parameters for the success of Lamb wave mode selectivity. The amplitude of the Lamb wave signal can be optimised by appropriate choice of the transducer lateral dimension. To validate the theoretical findings, transducers were embedded in both hard-set epoxy and uni-directional carbon fibre plates. Successful generation of the So mode is demonstrated by means of a scanning laser vibrometer.