Mechanical behavior of electroded piezoelectric material systems for smart device applications

Piezoelectric ceramics and composites play a significant role as active electronic components in many areas of science and technology, such as smart structures and MEMS devices [1-3]. In most of the applications as sensors, actuators, transducers and transformers in the field of such devices, piezoelectric ceramics are subjected to both high mechanical stresses and intense electric fields, hence, it is important for reliability and durability to investigate the linear and non-linear electromechanical response under these circumstances [4-9]. This presentation summarizes the recent observations on the mechanical behavior of electroded piezoelectric material systems for device applications through experimental and finite element characterizations. Two special topics are itemized below: 1 Bending of Smart Piezoelectric Devices A variety of strain-amplifying structures have been employed to obtain a larger displacement from piezoelectric ceramics to meet the requirements of many practical applications. In some practical structures such as bimorph, one major concern has been the polarization switching or domain wall motion of the piezoelectric layers [10-12]. First, we describe the electromechanical response of piezoelectric laminated actuators, and discuss the effects of DC electric field and polarization switching on the bending properties. We also examine the effect of electromagnetic fields on the non-linear bending response of piezoelectric/magnetostrictive laminated devices. Next, we present the results on the nonlinear bending behavior due to domain wall motion for the piezoelectric bimorph actuators and piezotransducers under AC electric fields. 2 Electromechanical Field Concentrations near Electrodes Stress and electric field concentrations in the neighborhood of an electrode tip in piezoelectric devices can result in mechanical and electrical degradation. It is therefore important to understand the electromechanical fields in the vicinity of the electrode and to improve the device's design and performance [13-15]. First, we look at the effect of applied voltage on the electromechanical field concentrations ahead of electrodes in piezoelectric devices. We have measured the strain near electrodes at various electrical loading conditions, and calculated the strain, stress and electric displacement concentrations. We have then made a comparison of strain concentration between experiment and simulation, and discussed a non-linear behavior induced by localized polarization switching. Next, we discuss the electromechanical field concentrations due to electrodes in partially poled multilayer piezoelectric film devices.