Composite piezaele. ctrics made from Calcium-modified lead titanate rods embedded in a polymer matrix have been evaluated for hydrophone applications. These composites behave quite differently from the conventional 1–3 composites made with lead zirconate titanate ceramics. Specifically, in the modified lead-titanate case the magnitude of the d31 coefficient is enhanced in the composite structure, and consequently the hydrostatic dhcoefficient is suppressed. Nevertheless, these composites exhibit a large gk coefficient and a remarkable pressure stability. An analysis shows that a substantial contribution to the composite's d31 coefficient arises from internal stresses which develop along the ceramic rods and produce a piezoelectric charge through the d33 coefficient of the ceramic. This effect is particularly pronounced in the composite structure of the modified lead-titanate ceramic since the ratio d33ld31 in this ceramic is exceptionally large.
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This work was supported in part by the Office of Naval Technology. We are indebted to: John %la. Donald Dorman. Michael Athanas, and Kevin McKeon of Philips Laboratories for help in making and characterizing the samples; and to Virgil Aptolim of the Naval Research Laboratory Underwater Sound Reference Detachment for help in the hydrostatic measurements.