Tilted Micro Air Jet for Flow Control

In this paper, we present an interesting method to microfabricate a tilted micro air jet generator. We used the well-know deep reactive ion etching (DRIE) technique in order to realize in a silicon substrate a double side etching. For aircraft and cars, micro air jets will take an important place for fluid control. Micro air jets are characterized by their speed, frequency and tilt. Usually, this micro air jets are produced by fluidic microsystems. We presented experimental results about micro tilted air jets. A comparison between finite element method simulation, theory and experimental results are performed to define the microsystem geometry leading a specific air jet angle

Image Compression Using Subband Wavelet Decomposition and DCT-based Quantization

International audienceThe aim of this work is to evaluate the performance of an image compression system based on wavelet-based subband decomposition. The compression method used in this paper differs from the classical procedure in the direction where the scalar quantization of the coarse scale approximation sub-image is replaced by a discrete cosine transform (DCT) based quantization. The images were decomposed using wavelet filters into a set of subbands with different resolutions corresponding to different frequency bands. The resulting high frequency subbands were vector quantized according to the magnitude of their variances. The coarse scale approximation sub-image is quantized using scalar quantization and then using DCT base quantization to show the benefit of this new optional method in term of CPU computationa1 cost vs restitution quality

Etude par microvibrométrie de films minces et de dispositifs micromécaniques

L'objectif de ce travail de thèse était de développer un système optique permettant la caractérisation sans contact du spectre de vibration et des modes de vibration de dispositifs micromécaniques et de modéliser les mesures pour différents types de dispositifs micromécaniques de test (micropoutres, microponts, membranes). Dans le chapitre II sont recensés les modèles analytiques et semi-analytiques existants qui décrivent le comportement dynamique des principaux dispositifs micromécaniques. Ces modèles sont comparés à des simulations par éléments finis effectuées avec le logiciel ANSYS et différents facteurs de corrections sont proposés pour les micropoutres et les microponts afin de tenir compte de la variation du module d'Young effectif avec la largeur des dispositifs ainsi que des imperfections géométriques et des contraintes résiduelles présents dans les microdispositifs réels. Dans le chapitre III les principales techniques de vibrométrie optique ponctuelles et plein champ et d'excitation des vibrations sont analysées à partir des besoins pour la caractérisation des microsystèmes ce qui a permis de sélectionner l'excitation piezoélectrique et la vibrométrie interférométrique comme étant des techniques adaptées pour nos expériences. Dans le chapitre IV le système de vibrométrie interférométrique qui a été développé est présenté et son fonctionnement et ses performances pour la mesure de spectres et de modes de vibration sont illustrées sur différents types de microdispositifs. Enfin les modèles et le vibromètre optique ont été appliqués à la caractérisation du module d'Young et des contraintes résiduelles de différents films minces à partir des fréquences de résonance de membranes, de micropoutres et de microponts. Dans le cas des membranes un bon accord a été obtenu entre les mesures par vibrométrie et par la technique de gonflement. Dans le cas des micropoutres et des microponts, les résultats montrent le rôle important de la configuration de l'encastrement sur la précision des résultats.The aim of this thesis work was the development of an optical system which allows non contact characterization of vibration spectra and vibration modes of micromechanical device and the modeling of the measurements for various type of micromechanical test device (cantilever microbeams, microbridges, membranes). Chapter II presents a survey of the analytical and semi-analytical models of the dynamical behavior of the main micromechanical devices. These models are compared with finite elements simulations with ANSYS software. Several correction factors are proposed for cantilever microbeams and microbridges in order to take into account the effective Young's modulus variation with devices as well as the geometrical imperfections and residual stress occurring in real microdevices. In chapter III, the main optical vibrometry techniques for point vibration spectra and vibration modes measurements are analyzed from the needs of microsystems characterization. This allowed to select piezoelectric excitation and interferometric vibrometry as suitable techniques for our experiments. In chapter IV, the optical vibrometer which has been developped is presented in details and its performances for vibration spectra and vibration modeshapes are illustrated on diffrent types of micromechanical devices. At last, models and the optical vibrometer have been applied to the characterization of the Young's modulus and residual stress of various thin films from the resonant frequencies of membranes, microbridges and mcantilever microbeams. In the case of membranes, results obtained by vibrometry and bulge test are in good agreement For cantilever microbeams and microbridges, it is demonstrated that the accuracy of results is largely dependent of the modeling of the clamping configuration.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Amplifier Limitation Mechanisms in Quartz Crystal Oscillators

International audienceThis work presents some results in connection with the amplifier limitation mechanisms in quartz crystal oscillators. These mechanisms were studied using the so called non linear dipolar method. This technique makes it possible to determine the close-loop operating conditions of the oscillator using open loop transient analyses. The well understanding of these limitation mechanisms should allow us to custom made quartz crystal oscillators, specifically for metrology and space applications. Key words: Dipolar method, dipolar impedance, quartz crystal oscillator, high-Q factor, time-domain analysis, SPICE

Les outils CAO pour les Oscillateurs à Quartz Dédiés aux Applications Spatiales

Ce travail présente une étude comparative des différents outils CAO pour les circuits oscillateurs à quartz dédiée aux applications spatiales. Les principales difficultés d'analyse et de conception de ses circuits sont traitées avec un certain nombre d'outils CAO. Les avantages et les limitations de chacun de ces outils sont également détaillés dans ce travail. A l'issue de cette étude, des critères de choix d'outil CAO sont proposés dans le but d'aider les concepteurs des circuits oscillateurs à quartz à choisir correctement l'outil le plus adapté à leur problème spécifiques

Parallel active mixing microdroplet array

In the micro- and nano-fluidics field, the mixing of droplets is a difficult challenge. This function is usually achieved by mixing two or more continuous flows via their injection in the same micro-channel. This strategy may be further improved by the active mixing introduced by an additional energy source plugged into the system to create flow instabilities. For example, ultrasonic mixers using stationary wave patterns or surface acoustic waves (SAW) were developed in order to decrease the mixing time and to improve the homogeneity of continuous-flow mixtures. Some micro-devices using microchanels even permit to generate micro-drops of reagents and to coalesce them in a carrier continuous phase. An alternative approach to continuous microfluidic systems is the manipulation of discrete droplets. The electrowetting-based linear-array droplet mixer, for example, proves that microdroplets can be transported, merged and actively mixed using an electrostatic field. Acoustic field can also be used for that purpose, several examples have been presented using, for the most part, high frequency vibrations such as SAW devices. In this paper, we introduce a parallel microdroplet mixing strategy based on local acoustic field generation using low frequency vibrations. An active acoustic mixer array was designed and fabricated. This microfluidic device permits the creation in parallel of an active mixture in a matrix of 25 microdroplets that are localized on a surface. It was designed to avoid contamination between droplets while they are excited. Experiments showing the independent and active mixture of droplets will be presented

Performing microdroplets mixing using an acoustic transducer with low vibration frequencies

In this paper, we introduce a parallel microdroplet mixing strategy based on local acoustic field generation using low frequency vibrations. An active acoustic mixer array was designed and fabricated. This microfluidic device permits the creation in parallel of an active mixture in a matrix of 25 microdroplets that are localized on a surface. It was designed to avoid contamination between droplets while they are excited. Experiments showing the active mixture of droplets will be presented

Robot intelligent utilisant la carte Altera DE1

National audienceUn robot commandé par un cœur NIOS II synthétisé sur une carte Altera DE1 a été réalisé. Le robot se déplace à l'aide de deux chenilles actionnées par deux moteurs à courant continu indépendants. Un distancemètre ultrasonore, piloté par I2C, permet au robot de détecter des obstacles et ainsi de les éviter. Un GPS (Global Positioning System) permettant de noter ces obstacles a quasiment été fini d'être mis en place