Abstract
Piezoelectric devices with complex electrode geometries often contain ferroelectric regions that experience little or no electric field and remain unpolarised. Since the un-poled and poled material properties differ it is desirable to account for these regions in a device when developing predictive models or to design piezoelectric transducers. The lack of published data on the elastic properties for un-poled ferroelectrics, specifically the numerous commercial compositions such as lead zirconate titanate, reflects the difficulty of experimental measurement. In this work, a method for predicting un-poled properties from more commonly available poled data has been developed. A new method of calculating these properties is presented which provides a rapid and practical solution to the problem of evaluating the isotropic stiffness and Poisson’s ratio for an un-poled ferroelectric material. The way in which this calculation has been derived and validated is presented and detailed comparisons are made with alternative methods and experimental data.
Highlights
Piezoelectric actuators increasingly employ complex electrode geometries for improved performance, such as multi-layer actuators, ring benders, active fibre composites with interdigitated electrodes and microelectro-mechanical systems (MEMS) [1,2,3]
These complex electrode arrangements produce non-uniform electric field distributions throughout the device that can provide enhanced actuation or lower driving voltages, but may result in ferroelectric regions which experience little or no electric field. Since these regions experience negligible electric fields that are below the coercive field (Ec), they can be regarded as un-poled ferroelectric material
The use of incorrect elastic constants in predictive models for piezoelectric transducers such as sensors, actuators and energy harvesters can lead to incorrectly calculated strains, sensor sensitivity or, for devices operating at resonant frequencies, errors in the frequency response of the device
Summary
Piezoelectric actuators increasingly employ complex electrode geometries for improved performance, such as multi-layer actuators, ring benders, active fibre composites with interdigitated electrodes and microelectro-mechanical systems (MEMS) [1,2,3]. These complex electrode arrangements produce non-uniform electric field distributions throughout the device that can provide enhanced actuation or lower driving voltages, but may result in ferroelectric regions which experience little or no electric field. For un-poled materials that are not piezoelectric the conventional electro-mechanical resonance techniques cannot be used to characterise the material
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