Studies of PZT/EPOXY and PMN-PT/EPOXY composites for ultrasonic transducer applications

Abstract

Two piezoelectric materials, lead zirconate titanate (PZT) and lead magnesium niobate-lead titanate (PMN-PT), have been characterized by using the resonance method and laser interferometry. PMN-PT (with 0.33PT) single crystal is an important new piezoelectric material for ultrasonic transducer and actuator applications. The stiffness constants and piezoelectric coefficients of PMN-PT are important parameters which have been measured in the present work. These are essential data if the crystal is to be used in device fabrication, but some of them are presently not available in the literature. Two types of composites have also been studied in this work: 1. Ring-shaped PZT/epoxy composites have been produced for fabricating Langevin sandwich-type transducers for high power ultrasonic applications, e.g. in the driver of an ultrasonic wire bonding transducer. The composites were prepared by a dice-and-fill technique in which poled PZT rings were cut in different patterns using a diamond saw. The grooves in the ceramic were filled with epoxy. Four composite rings were bolted together between two metal front and back plates to form the sandwich transducer. The performances of these composite transducers were characterized. It was found that the use of composite rings instead of ceramic rings in the sandwich transducer could eliminate the coupling of radial modes to the useful axial mode, thereby increaseing significantly the efficiency of the transducer. The composites have lower mechanical quality factor and the transducer fabricated using these rings have broader bandwidth. A US patent has been filed based on this work. 2. PMN-PT single crystals are reported to have very high electromechanical coupling factor k33 (>90%) compared to PZT (k33 - 60%). In order to exploit the advantage of the extra-high k33 of the crystal, a 1-3 PMN-PT/epoxy composite which PMN-PT rods embedded in an epoxy matrix has been fabricated by the dice-and-fill technique. Original results on the study of the coarsely-diced 1-3 PMN-PT/epoxy composite have been obtained and reported in this thesis.