Stress-biased cymbals using shape memory alloys

Cymbals and other flextensional transducers demonstrate high effective displacements due to the amplifying nature of the metal endcaps, while stress-biased RAINBOW actuators display high displacements due to enhanced 90 degrees domain wall translational processes that result from the tensile stress in the surface region of the lead zirconate titanate (PZT) layer created during manufacturing. A new class of transducers, called stress-biased cymbals (SBC), was developed that couples the operational principles of cymbal and stress-biased actuators. Pre-stressing the PZT in the cymbal was accomplished using a flat-trained shape memory alloy endcap. Hysteresis loops were measured using a Sawyer-Tower circuit for different pre-stress levels. Enhancements in the differential dielectric constant of more than 70% and the effective d(33) of the cymbal by similar to 57% were observed, suggesting greater 90 degrees domain wall motion in the SBC compared with the standard cymbal device. The stresses developed during the fabrication process were measured and compared with theoretical models. Additional performance characteristics including dynamic dielectric constant, loss, and radial resonance frequency of the devices are also reported.