Ferroelectric lead magnesium niobate–lead titanate single crystals for ultrasonic hydrophone applications

Ferroelectric lead magnesium niobate–lead titanate (PMN–PT) single crystals with a composition around the rhombohedral–tetragonal morphotropic phase boundary (65 mol% of PMN) were used to fabricate single-element needle-type hydrophones for measuring the spatial and temporal characteristics of medical ultrasonic transducers. PMN–PT single crystal was grown by a modified Bridgman method. Discs (0.5 mm thick) with normal along the 〈0 0 1〉 direction were cut and then poled by a dc field in the thickness direction. The single crystal has a high relative permittivity (εr∼4000) making it appropriate for small area hydrophone applications. Single-element needle-type hydrophones with this material as the sensing element have been fabricated and characterized. The hydrophones have flat frequency response and good receiving sensitivity over certain frequency range in the megahertz region.