Piezoelectric Single-Crystal 32-Mode Tonpilz Transducers: Design and Performance Evaluation for Broadband and High-Power Characteristics

Piezoelectric single crystals, with their high electromechanical coupling coefficient (k33 ≈ 0.9) and large piezoelectric constant (d33 > 1500 pC/N), have been actively researched for acoustic transducers to achieve high efficiency and broadband performance. However, despite their superior piezoelectric properties, the application of single crystals to high-power transducers has been restricted by limitations in driving field, temperature, and mechanical stress. To overcome these limitations, this study designed and experimentally validated a 32-mode Tonpilz transducer using [011]-poled single crystals, which exhibit higher electrical stability than the commonly used [001]-poled single crystals in 33-mode devices. The coercive field of [011]-poled single crystals was measured to be 8.81 kV/cm under 30 MPa-compressive stress—approximately twelve times higher than that of [001]-poled crystals. Based on these results, a 32-mode Tonpilz transducer was designed using [011]-poled PIN-PMN-PT single crystals. The design combined the longitudinal resonance of the piezoelectric stacks with the flapping mode of the head mass to broaden the bandwidth, while electrical and mechanical stress limits were considered to enable high-power operation. The fabricated transducer was experimentally characterized, showing good agreement between simulation and measurement, and source level measurements confirmed linear operation up to 1500 Vrms. These results demonstrate that [011]-poled single crystal-based transducers are promising candidates for high-power underwater acoustic projectors.