37 research outputs found
Silicon on Nothing Mems Electromechanical Resonator
The very significant growth of the wireless communication industry has
spawned tremendous interest in the development of high performances radio
frequencies (RF) components. Micro Electro Mechanical Systems (MEMS) are good
candidates to allow reconfigurable RF functions such as filters, oscillators or
antennas. This paper will focus on the MEMS electromechanical resonators which
show interesting performances to replace SAW filters or quartz reference
oscillators, allowing smaller integrated functions with lower power
consumption. The resonant frequency depends on the material properties, such as
Young's modulus and density, and on the movable mechanical structure dimensions
(beam length defined by photolithography). Thus, it is possible to obtain multi
frequencies resonators on a wafer. The resonator performance (frequency,
quality factor) strongly depends on the environment, like moisture or pressure,
which imply the need for a vacuum package. This paper will present first
resonator mechanisms and mechanical behaviors followed by state of the art
descriptions with applications and specifications overview. Then MEMS resonator
developments at STMicroelectronics including FEM analysis, technological
developments and characterization are detailed.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Estimating Mean Bedload Transport Rates and Their Uncertainty
Measuring bedload transport rates usually involves measuring the flux of sediment or collecting sediment during a certain interval of time Ît. Because bedload transport rates exhibit significant nonâGaussian fluctuations, their timeâaveraged rates depend a great deal on Ît. We begin by exploring this issue theoretically within the framework of Markov processes. We define the bedload transport rate either as the particle flux through a control surface or as a quantity related to the number of moving particles and their velocities in a control volume. These quantities are double averaged; that is, we calculate their ensemble and time averages. Both definitions lead to the same expression for the doubleâaveraged mean rate and to the same scaling for the variance's dependence on the length of the sampling duration Ît. These findings lead us to propose a protocol for measuring doubleâaveraged transport rates. We apply this protocol to an experiment we ran in a narrow flume using steadyâstate conditions (constant water discharge and sediment feed rates), in which the time variations in the particle flux, the number of moving particles, and their velocities were measured using highâspeed cameras. The data agree well with the previously defined theoretical relationships. Lastly, we apply our experimental protocol to other flow conditions (a long laboratory flume and a gravelâbed river) to show its potential across various contexts
L'acoustique picoseconde colorée (l'outil métrologique qu'attendait la technologie BAW [résonateur acoustique à onde de volume])
Cette thÚse a été réalisée pour le labo-commun ST-IEMN, dans le cadre du projet industriel de STMicroelectronics visant à réaliser des résonateurs à ondes acoustiques de volume (BAW : Bulk Acoustic Wave) pour des applications de fitrage RF. A l'instar du quartz, le BAW exploite la résonance du mode d'épaisseur d'une couche piézoélectrique comprise entre deux électrodes. Pour le passage en production de ces composants le contrÎle de la fréquence est un défi à relever, et il passe par une connaissance précise des paramÚtres mécaniques du dispositif. Pour cela, nous exploitons une technique expérimentale permettant de caractériser acoustiquement des empilements de matériaux en couches minces: l'acoustique picoseconde. Nous avons développé la particularité du montage de l'IEMN : l'accordabilité en longueur d'onde. A partir de cette spécificité, des études plus fondamentales ont donné lieu à l'élaboration de protocoles expérimentaux permettant d'augmenter le nombre de caractéristiques mesurables par acoustique picoseconde. L'exploitation de ces protocoles pour la caratérisation des matériaux liés au BAW nous a permis d'enrichir une base de données des paramÚtres nécessaires à la modélisation et à la conception des dispositifs. D'autre part, nous avons développé des méthodes d'analyse d'empilements complexes, qui ont pu Útre testées sur la version industrielle de la technique d'acoustique picoseconde. Nous avons finalement défini un protocole de suivi de procédé de réalisation des BAW, basé sur une métrologie par acoustique picosecondeThis PhD has been realized for the ST-IEMN Lab, in the frame of an industrial development at STMicroelectronics on Bulk Acoustic Wave (BAW) resonators. The operating principle of a BAW is based on the excitation of the thickness mode of a piezoelectric layer sandwiched between two electrodes. The control of the frequency is a challenging question for the mass production of such components, and requires a precise control of mechanical properties of the device. ln this work, we use an original experimental technique that enables the acoustic characterization of thin films stacks : colored picosecond ultrasonics. We particularly develop the specificity of the IEMN setup : the wavelegth tunability. Through fundamental studies we set up protocols and thus, increase the number of parameters that can be measured with the technique. This work enables us to feed a database ofparameters needed for the design and the modeling of the devices. We also work on complex stacks characterization, a part of the methods has been tested on the industrial version of picosecond ultrasonics. Finally we propose a metrological srategy, based on picosecond ultrasonics, in orde to assist the process of BAW resonators.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF
How bar generate sediment transport pulses in gravel-bed channels
We ran flume experiments with constant water dis- charge and sediment feed rate at the inlet. Experi- ments were conducted over long times (typically 600 h). The bars migrated downstream intermittently, producing the most important pulses. When the bar position was stable for a few hours, additional pulses resulted from sediment transfer from pool to pool, in the form of sediment waves (bedload sheets)
Catégorisations politiques et transformations sociales en agriculture
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