High performance tonpilz transducers utilizing d32-cut piezoelectric single crystals

High frequency sonar is becoming ever more important to the Navy through expanded use of unmanned underwater vehicles (UUV). Proposed missions for many UUV's involve shallow water operation where broad bandwidth is required making these applications ideal candidates to use single crystal piezoelectrics. In addition, many UUV sonar systems have commercial uses including oceanographic research, oil and mineral prospecting, salvage, and undersea equipment inspection and maintenance. The properties of single crystal piezoelectrics were exploited for broad bandwidth, high frequency sonar. Crystal sonar investigations based on Tonpilz transducers utilizing the "33" resonance mode have shown limitations on bandwidth due to less than ideal resonator aspect ratio. This is a result of the crystals' low elastic stiffness, which leads to short resonators with large lateral dimensions. To address this issue an alternative design was proposed utilizing the "32" resonance mode with the resonating length oriented along a special crystallographic cut. Crystals with this orientation are known to have high properties; d ₃₂ values as high as 1600 pC/N have been observed. Since prestress for such a design is applied perpendicular to the poling direction, "32" mode Tonpilz elements exhibit lower loss and higher reliability than "33" mode designs. The feasibility of such "32" mode Tonpilz resonators was presented as determined through property measurements and finite element analysis. A prototype single element Tonpilz will be constructed and tested in future research based on these results. The targeted application for this work is broadband (>100%), high frequency (45 kHz) synthetic aperture arrays for unmanned underwater vehicles.