Electromechanical Properties of a Ceramic d₃₁-Gradient Flextensional Actuator

We examined the static axial displacement of a ceramic d₃₁-gradient flextensional transducer both experimentally and theoretically. Two lead zirconate titanate systems, (PZT)/PZT and PZT/ZnO, were studied. The PZT/PZT transducers consisted of two PZT layers of different d₃₁ coefficients. The PZT/ZnO transducers consisted of a PZT and a ZnO layer. The PZT/PZT transducers were of an inner-type dome structure. The PZT/ZnO transducers were either flat, or had an inner- or outer-type dome structure by varying the thickness ratio between the two layers or the Sb₂O₃ content in the ZnO layer. An inner (outer)-type transducer has the large-d₃₁ layer on the inside (outside) of the dome structure. For the PZT/PZT transducers, the axial displacement varied with the thickness ratio and reached a maximum when the two layers had similar thickness, in agreement with the calculations. With a conductive nonpiezoelectric layer, the PZT/ZnO transducers had higher axial displacements, which varied with the thickness ratio and the Sb₂O₃ content, than the PZT/PZT transducers. With 6 wt % Sb₂O₃, the transducers were flat and the measured displacements at various thickness ratios were similar to the calculated values. With 4 wt% Sb₂O₃, the transducers were of an outer type. The measured axial displacements were about twice the calculated values, suggesting an enhanced d₃₁ value because of the tensile bending stress in the PZT layer. The scaled axial displacements of the PZT/ZnO transducers with 4 wt% Sb₂O₃ were comparable to that of the Rainbow transducers. With 8 wt% Sb₂O₃, the displacements of transducers with thin PZT layers (≤0.3 mm) were lower than the calculated values because of increased conductivity in the PZT layer.