Non-linear electromechanical behaviour of piezoelectric bimorph actuators: Influence on performance and lifetime

Abstract

Piezoelectric bimorph bender actuators find application number of areas, ranging from automotive to health care. High voltage operation in harsh environments poses ever more stringent demands on functionality and lifetime. In these high performance benders, the trade-off between functionality and lifetime becomes of increasing importance, and a model-based understanding is imperative for further tailoring actuator performance. An important issue in this is the non-linear electromechanical coupling and mechanical poling/depoling processes. PZT materials are known to exhibit non-linear stiffness when strained. This effect is attributed to domain re-orientation and can result in mechanical depoling. In bimorph benders where only one of the PZT members is actuated, the non-linear stiffness effect results in higher deflections than are predicted by linear elastic models. This effect is larger for soft PZT materials than for hard PZT materials. In this work, the non-linear behaviour of piezoelectric bimorphs was characterized by dynamic mechanical thermal analysis (DMTA). Unimorph benders were characterized in different configurations. Two different PZT materials (one soft, one hard) were used. The non-linear stiffness behaviour is included in a model for piezoelectric multimorphs. The multimorph model predictions are compared to measured deflection and blocking force of bimorph benders made from soft PZT material. The model incorporating non-linear stiffness predicts deflection and blocking force values more accurately than the linear model for the situation studied. Attention is paid to the stresses induced during poling of the bimorphs and their effect on performance and lifetime.

A short pulse (7 μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams

“…Van den Ende et al 35 measured the static deflection of a similar parallel bimorph, however, this cantilever was made of PZT5K material that had an even higher value of the piezoelectric charge constant, d 31 = −438 pm/ V. They measured the deflection with only one of the piezolayers activated, i.e., their reported deflection correlates to half of the full deflection that we report in Fig. 2.…”

“…32,33 Yao et al 33 studied and modeled the nonlinear static response of piezoelectric materials and applied these models to calculate the deflection and blocking forces of various unimorph and bimorph cantilevers. Furthermore, van den Ende et al 35 recently reported on the effects of nonlinear stiffness when bimorphs are strained when operated in the parallel configuration when only a single piezolayer is actuated. These nonlinear effects are due to mechanical domain reorientation and a model was developed which incorporates the nonlinear stiffness of the passive piezolayer.…”

Direct strain energy harvesting in automobile tires using piezoelectric PZT–polymer composites

“…Designs based on piezoelectric materials have also been considered many times [9,15]. Most are based on bender type energy harvesters [9,17] using ceramic lead zirconate titanate (PZT) in a mass-spring system. This brittle ceramic is not practical to use in automobile tires unless elaborate stress transfer mechanisms are employed [9], requiring very tight manufacturing tolerances in order to function properly.…”

Analysis and optimization of the active rigidity joint

“…For the case of the active rigidity joint under adverse loading, all of these conditions are true-actuator stress-strain behavior extends into a nonlinear region, only one layer is active instantaneously, and arbitrary actuator embedding is allowed. An iterative approach overcomes these obstacles similar to Ende et al (2008), another case where stiffness of at least one composite layer is dependent on strain. Rather than solving for the strains of equation ( 17) based on the solution to equations ( 15) and ( 16), an initial guess for actuator and upper face strains is made.…”