Laurent Hirsinger

Energy harvesting using vibrating structures excited by shock

Energy scavenging research shows a growing interest these last years. This paper aims to demonstrate the ability of micromachined vibrating structures to store mechanical energy and then to convert it into electrical energy through a piezoelectric plate. Such a micro power generator may be used as a mechanical to electrical energy transformer. The energy conversion consists in a mechanical shock enabling to convert low vibrating energy levels at very low frequencies (typically below 10 Hz for human being excitation source) to mechanical energy to the vibrating structure for which resonant frequencies are ranging from 10 kHz to 1 MHz. Moreover this basic low frequencies to high frequencies spectrum conversion enables to avoid frequency tuning designing that is required for adapting the frequency spectrum of the excitation source.

Structural and Mechanical Characterizations of Ni-Mn-Ga Thin Films Deposited by R.F. Sputtering and Heat-Treated

The near-stoichiometric Ni2MnGa ferromagnetic alloys are one of these smart materials, that show a great interest when they are deposited as a thin film by rf sputtering. These thin films of shape memory alloys (SMAs) are prospective materials for micro and nanosystem applications. However, the properties of the SMAs polycrystalline thin films depend strongly on their structure and internal stress, which develop during the sputtering process and also during the post-deposition annealing treatment. In this study, 1μm Ni55Mn23Ga22 thin films were deposited at 0.45 and 1 Pa of Ar and their composition, crystallographic structure, internal stress, indentation modulus, hardness and deflection induced by magnetic field were systematically studied as a function of the temperature of the silicon substrate ranging from 298 to 873 K and the vacuum annealing treatment at 873 K for 21 and 36 ks. A silicon wafer having a native amorphous thin SiOx buffer layer was used as a substrate. This substrate influences the microstructure and blocks the diffusion process during the heat treatment. The crystal structure of the martensitic phase in each film was changed systematically from bct or 10M or 14M. In addition, the evolution of the mechanical properties such as means stress, roughness, hardness and indentation modulus with the temperature (of substrate or of heat treatment) were measured and correlated to crystal structure and morphology changes. It is concluded that the response of a free-standing magnetic SMAs films to a magnetic field of 200 kA/m depends strongly on the martensitic structure, internal mechanical stress (mean and gradient) and magnetic properties. The free-standing annealed film at 873 K for 36 ks demonstrates a considerable magnetic actuation associated with bct or 10M or 14M martensitic structures.

3F-4 Experimental Evidence and Modeling of Microsliding on Cantilever Quartz Beam

The design of mechanical systems requires various studies in order to ensure an optimal behavior during operation. In particular, the study of its dynamic behavior makes it possible to evaluate the role of a connection in the energy dissipation mechanisms. In this context, an experimental setup dedicated to small structures has been developed to quantify damping due to microsliding at the beam-clamp interface. The mechanical characterization of the clamped connection is carried out by experimental dynamic tests on a free-clamped structure. The instantaneous frequencies and damping are identified by the wavelet transform technique of a slightly non-linear system. In parallel, numerical prediction of the equivalent damping is achieved thanks to the implementation of the regularized Coulomb law in a finite element model. A genetic algorithm and artificial neural networks are used to update the stiffness parameter and the friction coefficient. The optimized model is in good agreement with experimental results. It allows for determining the spatial distribution of microsliding and tangential force along the contact interface. The dissipated energy and equivalent damping are finally deduced according to the dynamic deflection of the free part of the beam.

P2E-4 Energy Harvesting Using Composite Silicon/Lithium Niobate Vibrating Structures

Energy scavenging research shows a growing interest these last years. This paper describes all the potential energy losses in an energy harvesting device. Such a micro power generator may be used as a mechanical to electrical energy transformer. A finite element piezoelectric optimization is performed on a cantilever structure and enables to show the best location for the piezoelectric plate.

Influence study of thermal effects on MEMS cantilever behavior

Aluminum nitride (AlN) films have piezoelectric properties that are already used for acoustic wave propagation in miniature high frequency bypass filters in wireless communication [1,2]. This is a promising material also for MEMS applications and sensors using surface acoustic waves, what have already been proposed. For actuation purposes, even if PZT films are frequently used for their better piezoelectric properties, AlN material still represents an alternative that have to be explored [3].