Properties of Transducer Ceramics under Maintained Planar Stress

In order to predict the performance of certain types of deeply submerged underwater transducers, measurements have been made of the properties of piezoelectric ceramics as a function of pressure, time, and electric field. Planar compressive stresses up to 35 000 psi were imposed on barium titanate and lead zirconate titanate ceramic by subjecting thin hollow spheres to uniform external pressure. With increasing stress, the dielectric constant, piezoelectric constant, coupling factor, and elastic compliance decreased by as much as 70%, part of the change being permanent but most of it reversible. The stability of the ceramic properties with duration and number of cycles of the imposed stress varied widely with ceramic composition. Large increases in high-field dielectric loss were observed at high stress in ceramics usually considered suitable for high-power projectors. The results indicate that transducers that utilize ceramic under planar stress may suffer significant degradation in performance when deeply submerged.