Vincent Walter

Uniaxial Electromechanical Behavior of a Soft PZT: Experiments and Modeling

The aim of this work is to collect a database from uniaxial experiments and model the material behavior. A soft PZT is tested in compression; the influence of stress rate seems to be negligible and the material accommodates to cyclic mechanical loadings. These responses are simulated by means of a phenomenological model taking into account the coupling between remnant strain and polarization thanks to a mechanically induced depolarization function.

Nonlinear dynamics of circular capacitive micromachined ultrasonic transducers

A multiphysics model for capacitive micromachined ultrasonic transducers (CMUTs) is developed taking into account the main sources of nonlinearities in the case of circular plates. The equation of motion is reduced to an asymmetric Duffing equation which is solved using the harmonic balance method coupled with the asymptotic numerical method. Multiple-valued solutions, indicating the occurrence of jump phenomena, are observed numerically and confirmed experimentally on measured frequency responses of micro-machined CMUTs based on anodic bonding of a SOI wafer on a glass wafer. This purely numerical approach allows designers to control the resonator bifurcation topology by tuning the design parameters and thus gives the possibility of driving the CMUT beyond its critical amplitude. As a consequence, the CMUT performances can be enhanced in terms of bandwidth and generated acoustic power.

Investigation of Output Mechanical Power Limits on High-Torque Electrostatic Actuators Using High-Frequency Complementary Metal Oxide Semiconductor (CMOS) Camera Combined with Image Processing Software

The following work investigates output mechanical power limits of electrostatic micromotors using stator/rotor contact interactions. Loading characteristics of micrometer size motors monolithically coupled with elastic polysilicon torque sensors are measured through an high-frequency complementary metal oxide semiconductor (CMOS) camera combined with a specific image processing software. Short duration video sequences recorded during the rotor braking are analyzed by tracking of a target pixel attached to the tested devices. Output mechanical power limits are measured through electrostatic probing on the wafer level within a few milliseconds. Experiments point out an unusual mechanical power per mass unit which is as high as 100 W/gr, considering driving frequencies on the order of 100 kHz.

Electromechanical characterization of screen-printed PZT thick films

Thick soft and hard-PZT films have been fabricated on different geometries of Alumina substrates using a screen-printing technique. Three mechanical characterization tests were set up to determine Youngs modulus of the films: dynamic, quasi-static and nanoindentation tests. A Youngs modulus around 52+/- 7 Gpa was calculated. The piezoelectric coefficient d31 was also investigated and is found to be close to -33pC/N. The fabricated films showed also good performances when used in damping control.