Increasing piezoelectric effect in radially polarized soft lead zirconate titanate (PZT) by pressure treating and its practical applications

Abstract

Soft PZT/NAVY type II ceramic material is commonly used for underwater acoustics sensing applications due to its softer composition and higher electromechanical coupling coefficient than Navy Type I or Type III materials but can also be used for projector applications. The effective coupling coefficient (k-eff) of soft PZT hollow cylinders can be improved from 0.33 to 0.40 (20%) under axial pressure treatment and remains stable with time. The sensitivity of dielectric constant and piezoelectric modulus to compressive stress for hard and soft tangentially polarization ceramics is shown to be less than radially polarized ceramics. Effect of planar stress in spheres at moderate and deeper depths are presented. An experimental method is introduced that utilizes an air-pressurized chamber to deliver stress loads to the piezoceramic. The electromechanical properties (including k-eff, dielectric constant, piezoelectric modulus, and compliance) are measured dynamically using an impedance analyzer and resonance/antiresonance techniques. Pressure treated cylinders with improved k-eff is shown to be suitable for application that utilize pressure equalized (free-flooded) transducer designs and for air-backed transducer designs under moderate depths. The improved k-eff improves the power factor bandwidth of the transducer is further studied using equivalent electrical circuit model including the effect of external pressure.