Experimental results on pre-stressed piezoelectric cantilevers near resonance

Piezoelectrics play a leading role in many applications, ranging from simple commercial products, to microcantilevers in atomic force microscopes. Yet, they still provide some surprises. One such surprise is the enhanced performance of pre-stressed unimorph actuators known as high displacement or THUNDER actuators. They were originally developed by NASA. There is still some debate about how the higher performance is obtained. We measured the displacement response to an applied ac voltage at or near the first resonant mode. Most of our experimental results compare favorably with a nonlinear response theory developed by Wolf and Gottlieb for traditional bimorphs and unimorphs. However, some results on the higher order piezoelectric coefficients are difficult to reconcile with this theory. It is not yet clear if the differences are structural in nature or if they are due to modified (engineered) ferroelectric domains resulting from the pre-stress. NASA Grant number: 0051-0078