The flexoelectric effect of solids is an electromechanical conversion mechanism that occurs in all dielectric materials, often together with other effects such as the piezoelectric. Currently, piezoelectric, electrodynamic and electrostatic conversion mechanisms are mostly used in actuators, some of them use dielectrics. The converse flexoelectric effect, has not yet been widely explored as an additional effect in these dielectric materials. A broad understanding of this effect could lead to new applications with a wider range of materials. In this paper, we attempt to determine the contribution of the converse flexoelectric effect in a lead zirconate titanate (PZT) piezoelectric soft ceramic. For this purpose, strongly varying electric fields were applied to capacitive electrode arrangements. The electrodes were deposited on one side of PZT-wafers (PIC151). Sinusoidal as well as pulsed voltage signals were applied to the electrodes. Doing so, the samples showed displacements in all three spatial directions. To separate the converse flexoelectric effect from the piezoelectric, displacements were measured at different temperatures between 20°C and 350°C i.e. even above the Curie temperature (Tc). The resulting deflection follows the electrical input signal at all temperatures. Because piezoelectric effects can be excluded above the Tc, another effect must be responsible for the displacement. The significant displacement of 30 to 40% in comparison to room temperature is attributed to the flexoelectric effect.
Current state-of-the-art systems for measuring movements at a microscopic scale in MEMS mostly rely on laser Doppler vibrometry (LDV). However, a major downside of LDV is that only one point at a time can be tracked and only in the direction of the incident laser beam. On the other hand, stroboscopic video microscopy (SVM) allows monitoring the inplane displacements of all points in the field of view simultaneously. Commercially available vibrometry systems often provide an SVM mode. However, their resolution typically ranges from several to tens of nanometers. In contrast, some experimental SVM systems described in literature have achieved resolutions down to tens of picometers. Here we compare the performance of our self-built SVM setup to a modern commercial LDV device in characterizing piezoelectric actuators made from sintered lead zirconate titanate (PZT). The samples were stimulated with sinusoidal signals to induce surface strain in all three directions of space. Maps of the induced strain fields were recorded in-plane with SVM and out-of-plane with LDV. Our measurements prove that SVM, as realized in our setup, can be a cost-effective alternative to LDV for monitoring and characterizing of MEMS with sub-nanometer accuracy. Especially at low frequencies and when applied to challenging samples, SVM can outperform LDV in terms of accuracy and time efficiency.
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