Comparison of the frequency and physical nature of the lowest order parasitic mode in single crystal and ceramic 2-2 and 1-3 piezoelectric composite transducers.

This work describes an investigation into the first order parasitic mode (i.e., that closest to the fundamental thickness mode) that can occur in 2-2 and 1-3 thickness drive piezoelectric composite transducers. Specifically, the authors compare the performance of piezoceramic and piezocrystal composites with a common passive phase. A local Lamb wave approach is used to describe the generation of such modes, and the validity of this theory is investigated over the entire volume fraction range. It is shown that, when the parasitic mode is primarily generated by Lamb wave activity in the passive phase, both active materials demonstrate similar behavior. However, at higher volume fractions, the first order mode is related to the lateral resonance of the active material, and quite different behavior may be observed between the two sets of devices. The phase velocity of the parasitic modes in each device configuration was investigated by a combination of experimental measurement on a number of transducers along with simulations using the finite-element code PZFlex. Both 2-2 and 1-3 composites made from the single crystal materials pzn-4.5%pt, pzn-8%pt, and pmn-30%pt were investigated along with composites made from pzt5h ceramic. The PZFlex results are compared with experimental impedance analysis and laser scanning of surface displacement, with good agreement demonstrated. By comparing two very different active materials, additional insight into parasitic resonant activity within composite devices is demonstrated.