Anisotropic laminar piezocomposite actuator incorporating machined PMN-PT single-crystal fibers

The design, fabrication, and testing of a flexible, laminar, anisotropic piezoelectric composite actuator utilizing machined PMN-32%PT single-crystal fibers is presented. The device consists of a layer of rectangular single-crystal piezoelectric fibers in an epoxy matrix, packaged between interdigitated electrode polyimide films. Quasistatic free-strain measurements of the single-crystal device are compared with measurements from geometrically identical specimens incorporating polycrystalline PZT-5A and PZT-5H piezoceramic fibers. Free-strain actuation of the single-crystal actuator at low bipolar electric fields (+/- 250 V/mm) is approximate to 400% greater than that of the baseline PZT-5A piezoceramic device, and 200% greater than that of the PZT-5H device. Free-strain actuation under high unipolar electric fields (0-4 kV/mm) is approximate to 200% of the PZT-5A baseline device, and 150% of the PZT-5H alternate piezoceramic device. Performance increases at low field are qualitatively consistent with predicted increases based on scaling the low-field d(33) piezoelectric constants of the respective piezoelectric materials. High-field increases are much less than scaled d(33) estimates, but appear consistent with high-field free-strain measurements reported for similar bulk single-crystal and piezoceramic compositions. Measurements of single-crystal actuator capacitance and coupling coefficient are also provided. These properties were poorly predicted using scaled bulk material dielectric and coupling coefficient data. Rule-of-mixture calculations of the effective elastic properties of the single-crystal device and estimated actuation work energy densities are also presented. Results indicate longitudinal stiffnesses significantly lower (50% less) than either piezoceramic device. This suggests that single-crystal piezocomposite actuators will be best suited to low induced-stress, high strain, and deflection applications.