The study of Lamb wave dispersion in piezoelectric plate transducers

This paper describes a methodology for the prediction of Lamb wave dispersion in piezoceramic and 1-3 piezocomposite materials. The approach is applicable to both experimental measurement and theoretical modelling using a time domain finite element (FE) code, PZFlex. Initially, the dispersion characteristics of polymeric, poled and unpoled Lead Zirconate Titanate type 5H (PZT5H) piezoceramic materials are derived. The technique is then extended to dual-phase materials, whereby a series of piezoceramic pillars or planks are embedded in a polymer matrix to form a 1-3 piezocomposite material. Finally, the influence of Lamb wave propagation on transducer behaviour is studied for a single-element rectangular transducer, defined in the centre of a piezocomposite substrate. The Lamb wave modes supported in the structure are identified, and their degrading effect on element surface displacement and beamwidth noted. A second transducer array, incorporating a high-loss polymer in the passive phase of the 1-3 material is examined. The improvement in element beamwidth for this device illustrates the benefits of ensuring Lamb wave propagation in any transducer structure is kept to a minimum through judicial transducer design. Throughout this investigation, excellent agreement is achieved between the measured data gathered from devices fabricated within the Centre for Ultrasonic Engineering, and that generated from the PZFlex finite element (FE) code.