The actuation characterization of cantilevered unimorph beams with single crystal piezoelectric materials

An experimental and theoretical electromechanical characterization of beam-like, uniform cross-section, unimorph structures employing single crystal piezoelectrics is presented. The purpose of the research is to understand and compare the actuation capabilities of several piezoelectric materials and substrate configurations so that optimal design choices can be employed in lightweight, low power aerodynamic applications. Monolithic devices made from three kinds of piezoelectrics-single crystal PMN-PZT (lead magnesium niobate-lead zirconate titanate) and the polycrystalline PZT-5A and PZT-5H types-are compared in a unimorph cantilevered beam configuration. A total of 24 unimorph specimens are fabricated and the validity of existing models is examined through experimentation. The tip velocity response to harmonic voltage excitation is measured and compared to the analytical prediction with the perfect bonding assumption. Summarizing, it was confirmed that the substrate-to-piezoelectric thickness ratio and substrate modulus are the important design parameters in determining the measured output of the unimorphs and the accuracy of the model prediction. The single crystal piezoelectrics demonstrated actuation authority two to four times higher (measured in terms of peak displacement per applied voltage) when compared to the polycrystalline piezoceramics for the same substrate material and geometry choice. In contrast to the higher actuation output, practical implementation issues are noted for the single crystal devices. The lack of grain boundaries (as in the polycrystalline material) makes the single crystals very 'brittle' and susceptible to stress concentrations. Another important limitation is the low transition temperature, which limits the use of conventional solder materials in creating electrical connections.