Designing next generation flextensional transducers by stress engineering

This doctoral research is focused on engineering the stress distribution in the metal endcaps and active piezoelectric disk of cymbal flextensional transducers to enhance piezoelectric response. This dissertation describes the design, fabrication, characterization and modeling of three novel transducers. 2D and 3D piezoelectric models were created using ATILARTM for the donut and wagon wheel devices, respectively, to predict the flextensional resonance frequency (fr) and coupling coefficients (keff). Good agreement was observed between the simulations and the measured values. It was found that the wagon wheel devices demonstrate displacement that is 35% greater, and less hysteretic, than cymbals with similar dimensions. The effect of various endcap dimensional parameters on the fr and keff of the donut devices were modeled. Experimentally measured values suggest that these devices possess keff values that are ∼ 50% higher than comparable cymbals. A novel method of pre-stressing the PZT disk to take advantage of the extrinsic contribution to piezoelectric response in the cymbals and maintain the amplification mechanism associated with the endcaps was undertaken by using a shape memory alloy for the endcap. The resultant devices are called stress-biased cymbals (SBC). A wide variety of experimental techniques were used to study the effect of pre-stress on the dielectric and piezoelectric response of the SBC devices. The magnitude of the pre-stress applied to the PZT was measured and compared with the theoretical model. Enhancements in the differential dielectric constant of more than 70% and the effective d33 of ∼ 57% were observed, suggesting greater 90° domain wall motion in the SBC. A decrease in the coercive field and the radial resonance frequency of the SBC with increasing pre-stress was observed indicating electrical softening.