Piezoelectric Composite Materials for Ultrasonic Transducer Applications. Part I: Resonant Modes of Vibration of PZT Rod-Polymer Composites

Abstract

Abstmcr-The objective of the present work was to gain a deeper mensions of the transducer are much smaller than the understanding of the behavior of lead zirconate titanate (PZT) polymer composites for applications such as ultrasonic medical diagnosis in the megahertz frequency range. These composites were originally developed for low-frequency hydrophone applications. The PZT rod-polymer composites have been prepared with five to 30 volume percent PZT using 0.28 mm and 0.45 mm rods. In a disc of PZT rod-polymer composite material, there are three principal types of resonance: the planar mode, the thickness mode, and various lateral modes caused by the regular periodicity of the PZT rod in the composite. These resonance modes have been studied with the following techniques: 1) electrical impedance measurement as a function of frequency and 2) laser probe dilatometry of the dynamic displacement as a function of frequency and position in the composite lattice. The observed resonance behavior is found to be a result of lateral interactions in the composite through the epoxy medium. The effect of temperature on the electromechanical properties of the composite has also been investigated. Implications of these results for optimizing the design of ultrasonic transducers are discussed.