The use of piezoelectric materials for power harvesting has attracted significant interest over the past few years. The majority of research on this subject has sought to quantify the amount of energy generated in power harvesting applications, or to develop methods of improving the amount of energy generated. Usually, a monolithic piezoelectric material with a traditional electrode pattern and poled through its thickness is used for power harvesting. However, in recent years several companies and research institutions have begun to develop and market a broad range of piezoelectric composite sensor/actuator packages, each conceived for specific operational advantages and characteristics. Commonly, these devices are employed in control and vibration suppression applications, and their potential for use in power-harvesting systems remains largely unknown. Two frequently implemented design techniques for improving the performance of such actuators are the use of interdigitated electrodes and piezofibers. This paper seeks to experimentally quantify the differences in performance in power-harvesting applications between several of these new actuators and to identify the reasons for their relative performance characteristics. A special focus on the structural and compositional differences between each actuator is incorporated in the discussion of the effectiveness of each actuator as a power-harvesting device.

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 freestrain 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 approximately 400% greater than that of the https://ntrs.nasa.gov/search

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The design, fabrication, and testing of a flexible, planar, 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 approximately 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 (0-4kV/mm) is approximately 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 freestrain 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. Rules-of-mixtures 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.

Economic problems in the optimal management of strategic resource stockpiles can be rigorously studied and solved by formulating them as optimal control problems in continuous time. Often, the real economic systems and stockpiling scenarios of interest exhibit both stochastic features and input saturation effects. Building on work to account for saturation effects into basic optimal stockpile problems, the following paper solves a basic optimal stockpile model with a stochastic saturation limit as well as a stochastic solution interval.