Tailoring the Properties of Composite Piezoelectric Materials for Medical Ultrasonic Transducers

Abstract

Transducers for medical ultrasonic imaging have been made from composite piezoelectric materials. This paper describes a simple physical model for the material properties which govern the thickness-mode oscillations in thin plates of PZT-rod/polymer composites. We consider the case where the lateral periodicity of the rods is much smaller than all relevant acoustic wavelengths. Expressions are derived for the effective material parameters in terms of the properties of the constituents. The composites' properties can then be tailored to device requirements by choosing appropriate components and by varying the volume fraction of piezoceramic. Our analysis reveals the need for a trade-off between the desired lower acoustic impedance and the undesired smaller electromechanical coupling that occurs as the volume fraction of piezoceramic is reduced. The predictions of this model are in good agreement with measurements made on rod-composite plates containing 5 to 35 percent PZT.