Diapason

Résumé

En musique, le diapason est à la fois un instrument matériel produisant un son de référence et cette référence elle-même : un son dont la hauteur est dans presque tous les cas un la (corde à vide du violon). Cette référence permet aux musiciens d'accorder ensemble leurs instruments de musique. La note de référence standard est le la 440, qui fixe la fréquence du la3 à à 20 °C. Néanmoins, le diapason des orchestres symphoniques professionnels en France et en Europe est basé sur le la3 à 442 Hz donné par le hautbois. Les diapasons des instruments à vent à trous latéraux montent lorsque ces instruments sont joués (« chauffent ») et sont conçus pour cette hauteur de note. Il existe également des diapasons soufflés à plusieurs tubes pour les instruments à cordes, à quatre tubes pour les violons et six pour les guitares. Des appareils électroniques, parfois appelés accordeurs, permettent également d'accorder des instruments comme le violon, en émettant les notes : mi - la - ré - sol cal

Source officielle

https://fr.wikipedia.org/wiki/Diapason

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Effective quality factor tuning mechanisms in micromechanical resonators

Azadeh Ansari, Luis Guillermo Villanueva Torrijo

Quality factor (Q) is an important property of micro- and nano-electromechanical (MEM/NEM) resonators that underlie timing references, frequency sources, atomic force microscopes, gyroscopes, and mass sensors. Various methods have been utilized to tune the effective quality factor of MEM/NEM resonators, including external proportional feedback control, optical pumping, mechanical pumping, thermal-piezoresistive pumping, and parametric pumping. This work reviews these mechanisms and compares the effective Q tuning using a position-proportional and a velocity-proportional force expression. We further clarify the relationship between the mechanical Q, the effective Q, and the thermomechanical noise of a resonator. We finally show that parametric pumping and thermal-piezoresistive pumping enhance the effective Q of a micromechanical resonator by experimentally studying the thermomechanical noise spectrum of a device subjected to both techniques. (C) 2018 Author(s).

2018

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Hill et al. reported for the first time in 1978 the formation of refractive-index gratings in germanium doped silica fibers exposed to UV laser radiation. Since then many studies have been performed on fiber gratings and a widespread range of applications has been found. For example, gratings are today used as sensors, for the measurement of strain, temperature and pressure, or in telecommunications, as multiplexers, filters, dispersion compensators, mode converters and fiber laser mirrors. The aim of this work is to conceive and to realize a fast and broadband tunable optical filter device for telecommunications. Up to now, no in-fiber filters combining wide tuning range and high tuning speed have been reported in literature. The main elements of the realized filter are two piezoelectric stack actuators permitting to push and/or pull the optical fiber exploiting the Bragg grating strain sensitivity. Two independent control loops are used to control and to adjust the actuators position. To minimize bending problems during compression, the fiber is inserted in a specially conceived guiding system. Any kind of fiber grating, e.g. Bragg, chirped, ... could be strained. However, the tuning range is inversely proportional to the strained length. A prototype, integrating the piezoelectric stack actuators, the control loops, the guiding system and the fiber grating, was realized. It operates both in reflection and in transmission. Maximum tuning speeds are around 19 nm/ms with setting times less than 1.5 ms. A tuning ranges of ∼45 nm was obtained for a grating of 2.5 mm length. The repeatability in the wavelength selection is better than 0.3 nm. This prototype is tunable over the Erbium Doped Fiber Amplifier range without spectral, reflectivity and bandwidth changes. This device is designed to work with a channel spacing of 100 GHz according to the International Telecommunications Union specifications for Wavelength Division Multiplexing systems. In addition this filter has been successfully used to continuously tune the output mirror of a cw praseodymium doped all fiber laser emitting in the 1.3 μm region. This device is of potential use in telecommunication networks for wavelength multiplexing, switching and routing or as wavelength selective filter.

EPFL1999

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In this paper, we report on the integration technique and fabrication of a scanning probe interrogating the location of charges and their tracks inside quantum devices. Our unique approach is to pattern the charged sensor into a high topography micromechanical structure. A single-electron transistor (SET) is directly integrated onto the microfabricated cantilever that extends out from the body of a scanning force microscope (SFM) probe of standard dimensions. In a novel tactic and by reversing their traditional roles, a tuning fork (TF) completes the probe to provide the self-actuating and self-sensing qualities necessary for an oscillatory force sensor. We show sharp edges on the Coulomb diamonds, indication that the SET fabrication step yields devices of high quality. We demonstrate topographical scans with this probe. All stages of the fabrication process are executed on batches of probes which is an essential step away from the time-consuming and individual preparation of other implementations. It opens the door to a more reproducible and large volume production.

2010

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