Single-crystal ferroelectrics for sonar devices

Abstract

Single-crystal ferroelectrics or piezocrystals were recently introduced into the electroactive materials community. The 33-mode electromechanical coupling factor of piezocrystals is typically greater than 0.90, which is significantly larger than typical values for piezoelectric ceramics (0.62–0.74). For sonar projector applications this large, k33 has been responsible for more than doubling the bandwidth of active sonar arrays over what is currently achievable with ceramics. More recently, a crystal grower produced a cut of lead magnesium niobate-lead titanate (PMN-PT) single crystal with piezoelectric shear coefficient values of 7000 pm/V and shear coupling factors of 0.97. (For PZT5H, d15 is 730 pm/V.) This piezocrystal d15 coefficient implies significantly improved sensitivity and signal-to-noise ratio for accelerometers and hydrophones, while the high coupling promises bandwidth increases greater than those realized in 33-mode projectors using piezocrystals. The 31-mode is also being investigated. By measuring the response of the materials to high- and low-level electrical bias and excitation fields, mechanical prestresses, over temperature, the material’s effective material properties as a function of these operational variables have been determined. [This work sponsored by ONR and NUWC ILIR.]