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There are various energy dissipation mechanisms that affect the dynamic response of microstructures used in MEMS devices. A cumulative effect of such losses is captured by an important characteristic of the structure called Quality factor or Q-factor. Estimating Q-factor at the design stage is crucial in all applications that use dynamics as their principle mode of operation. A high Q-factor indicates sharp resonance that, in turn, can indicate a broad flat response region of the structure. In addition, a high Q-factor typically indicates a high sensitivity. Microstructures used in MEMS are generally required to have much higher Q-factors than their macro counterparts. However some damping mechanisms present in microstructures can reduce the Q-factor of the structure significantly. In the present work, we investigate the dependence of Q-factor on the squeeze film damping an energy dissipation mechanism that dominates by a couple of orders of magnitude over other losses when a fluid (e.g., air) is squeezed through gaps due to vibrations of a microstructure. In particular, we show the effect of nonlinear terms in the analysis of squeeze film damping on the Q-factor of a structure. We also show the effect of rarefaction, surface roughness along with their coupled effect and with different boundary conditions such as open border effect, blocked boundary effect on the squeeze film damping. Finally, we develop similitude laws for calculating squeeze film damping force in up-scaled structures. We illustrate the effects by studying various type of microstructures including parallel plates, beams, plate and beam assemblies such as MEMS microphone, vibratory gyroscope etc. We view the contributions of this work as a significant in investigating and integrating all important effects altogether on the squeeze film damping, which is a significant factor in the design and analysis of MEMS devices.

Afin de pallier aux problèmes dus aux limites de détection des capteurs et des détecteurs usuels, un système de préconcentration est indispensable. Ce microcomposant permet d’accumuler le ou les vapeur(s) à détecter à l’aide d’un adsorbant et permet de les libérer sous l’effet d’une montée brutale de la température vers un détecteur. Une amplification de la concentration et donc du signal est ainsi obtenue.Cette thèse poursuit le développement d’un préconcentrateur pour la détection de vapeurs toxiques et d’explosifs. Ce préconcentrateur sera constitué d’un microcomposant en silicium rempli d’un adsorbant et muni d’une résistance de chauffage sur sa face inférieure. Des capillaires métalliques permettent d’assurer la circulation du gaz dans le dispositif. Différents types de préconcentrateurs ont été développés avec différents adsorbants afin satisfaire les conditions pour des applications concernant les composés organiques volatils (COV) et les explosifs. L’optimisation des phases d’adsorption et de désorption est cruciale pour le procédé.Le couplage entre un micro-chromatographe et un préconcentrateur a été réalisé et a montré l’apport de ce microcomposant pour la chromatographie. L’analyse d’un mélange de COV a pu être réalisée avec des concentrations initiales de l’ordre de 40 ppb alors que la limite de détection de l’appareillage était de quelques ppm. Un facteur d’enrichissement de 800 a été atteint.L’avantage de l’utilisation du silicium poreux a également été mis en évidence pour l’adsorption de gaz avec des faibles pressions de vapeur saturante. Cette propriété est intéressante pour la préconcentration de vapeur d’explosifs. / In order to overcome problems due to the conventional sensors detection limits, a preconcentration system is required. Accumulation of vapor(s) for detection is possible with an adsorbent and allows releasing them toward a detector, under the effect of a sudden rise of the temperature. Amplification of the concentration and the signal are obtained.This thesis continues the development of a preconcentrator for the detection of toxic gas and explosives. This preconcentrator is made of a silicon microcomponent filled with an adsorbent and a heater at its back. Two metal capillary allow ensuring the gas flow into the device. Various designs of preconcentrators were developed with different adsorbents to satisfy the requirements for volatile organic compounds (VOCs) and explosives applications.The optimization of adsorption and desorption phases is very important for the process.The coupling between a micro-chromatograph and a preconcentrator was conducted and showed the contribution of the microcomponent to the chromatography. Analysis of a VOCs mixture was achieved with initial concentrations in the order of 40 ppb, whereas the detection limit was of a few ppm. An enrichment factor of 800 was achieved.The advantage of using porous silicon was also demonstrated for the gas adsorption with low saturation vapor pressure. This result is interesting for explosive vapor préconcentration.