Modified single crystals for high-power underwater projectors

Underwater electroacoustic projectors using single crystals based on the lead magnesium niobate-lead titanate (PMNT) composition were investigated. The large electromechanical coupling coefficient (k₃₃ >; 0.90) and piezoelectric coefficient (d₃₃ >; 1500 pC/N) of PMNT have been demonstrated to improve transducer bandwidth and source level relative to conventional piezoelectric ceramics. The low mechanical quality factor (Q_M <; 200) and low temperature stability (T_RT <; 95°C) of PMNT, however, limit its utility in high-power, high-duty-cycle applications. Use of modified single crystals was shown to result in transducers which exhibit up to 5 dB improvement in source level over PMNT when operated at resonance. Compared with a PZT4 transducer, these modified crystals offer similar source level and power handling capability at resonance, but the available bandwidth is doubled and a 6 dB improvement in maximum source level is achieved when driven off resonance.