Session: 4G

Stacks of longitudinally polarized piezoelectric elements with alternating polarity have long been used to achieve high acoustic outputs, such as in lithotripter transducers. Crystals exhibiting a shear piezoelectric response can also be stacked in this manner, and the alignment of their shear axes is a strong factor in their behavior. For crystals whose piezoelectric response includes both longitudinal and shear, the two orthogonal modes can be considered to exist within separate virtual crystals which are electrically in parallel (common electrodes) but mechanically uncoupled (orthogonal modes). The goal of this research is development of multi-mode transducers, which can detect and separate longitudinal and shear modes by exploiting this electromechanical behavior. Transducers were constructed using stacks of lithium niobate crystals having three different cuts: 36◦ Y-cut (having 4 MHz longitudinal resonance), 41◦ X-cut (having 2.5 MHz shear resonance), and 10◦ Y-cut (having both 4.15 MHz longitudinal and 2.5 MHz shear resonances). Single-mode stacks were constructed using pairs of 36◦ Y-cut and of 41◦ X-cut crystals with their polarizations anti-parallel. To achieve dual-mode, 10◦ Y-cut crystals were stacked with their longitudinal polarizations anti-parallel, and their shear polarizations parallel. When the resulting transducers were excited by longitudinal and shear incident modes, the electrical responses from the separate crystals were found to exhibit in-phase and out-of-phase nature according to their relative polarizations. These results suggest that these signals might be combined to separate longitudinal and shear modes incident simultaneously on the transducer.