V. Walter

Active damping of a micro-cantilever piezo-composite beam

Thick PZT films are of major interest in the actuation of mechanical structures. One of the promising fields deals with active damping. Since it is a dynamic application, hard-PZT type of screen-printed films are suited to this kind of use. Nevertheless, the drop in dielectric, ferroelectric and piezoelectric properties induced by the fabrication process is a serious constraint and it needs to be evaluated. The first section of this paper will present the mechanical system used for the experimental investigations. These investigations look to quantify the electromechanical properties of the films once the deposition process is achieved. The experimental observations highlighting the efficiency of hard-PZT thick films in active damping despite the drop in the electromechanical properties will then be considered. The control strategy used in the experiments can be called pseudo-direct-velocity feedback. Then the constitutive relations of the composites will be needed to derive the roots locus analysis by means of finite element modelling on one hand and through the roots of the partial derivative equations on the other hand. The unconditional stability of the uncollocated system will be demonstrated and its typical asymptotic behavior when the gain tends towards infinity will be explained.

A nonlinear electromechanical model for ferroelectric materials: application to soft-PZT thick films screen-printed on alumina substrate

Motivated by experimental observations made on soft-PZT/alumina cantilever bimorphs, a nonlinear electromechanical model is presented describing the characteristic phenomena of ferroelectricity: the dielectric hysteresis, the butterfly loop, and the ferroelastic hysteresis. This model uses a phenomenological formulation, written within the general framework of thermodynamics of irreversible processes. The one-dimensional formulation of the model is successfully validated using experimental data from the literature. The model is used to predict the electromechanical behavior of a PZT/alumina cantilever bimorph. The results of the simulations are very promising.

Active damping with piezoelectric MEMS devices

Thick PZT films are of major interest in the actuation of mechanical structures. One of the promising fields deals with active damping. Piezoelectric actuators have proved to be effective control devices for active stabilization of structural vibrations and are now used in a wide range of engineering applications. Piezo materials can be integrated in various structural components as distributed sensors or actuators. In this context, Micro-Electro-Mechanical Systems appear very attractive in improving the mechanical efficiency of structural active control. These systems can be distributed on a structure and are very powerful since it induces a very high level of stress density. They can effectively present a good opportunity in a large class of problem. The studied micro controlling system is a micro beam totally covered by a piezoelectric, PZT, film. This sample system can be considered as a suspension element being able to support very light and sensitive systems like frequency generator or MEMS sensors. We first describe modeling and the experimental updating methods used to characterize piezoelectric behavior. Secondly, we show the observations highlighting the efficiency of hard-PZT\ thick films in active damping of sensitive devices by using pseudo direct velocity feedback.

Dynamic characteristics of circular CMUTs with air-filled cavities

Our work deals with the study of the dynamic characteristics of a single circular CMUT transducer under squeeze film damping effect. A simplified analytical approach is developed for parallel plate approximation for the electromechanical behavior and the squeeze film damping. Analytically calculated results demonstrates, that trends of resonant frequency with bias voltage are defined by the ratio of air spring constant to mechanical spring constant. At the same time FEM multiphysics model is built to define the influence of membrane flexibility and venting boundary conditions to the dimensionless viscous and elastic damping forces. FEM study shows the presence of viscous loss in the sealed air-filled cavity and the insensitivity of squeeze film damping forces to the type of lateral venting boundary conditions in high squeeze number region which is typical for CMUT operation. Finally, the experimental dynamic characterization is conducted on CMUT with 67 μm - 167 μm radii fabricated utilizing an anodic bonding technology. Experimental data are in a good agreement with the results of multiphysics FEM calculation, which take into account bias voltage, initial plate deflection, radiation loss and squeeze film damping.