Capteur piézoélectrique

Résumé

thumb|Schéma de principe de fonctionnement d'un capteur piézoélectrique Un capteur piézoélectrique est un capteur utilisant l'effet piézoélectrique afin de mesurer des grandeurs physiques telles que la pression, l'accélération, ou tout autre grandeur physique engendrant des contraintes ou des déformations mécaniques par le biais de matériaux actifs (magnétique, électrique, thermique, mécanique...). En effet, la notion de capteur piézoélectrique peut être étendue à des dispositifs couplant l'utilisation de matériaux piézoélectriques avec celle d'un matériau actif (matériau au sein duquel existe un couplage physique entre plusieurs grandeurs physiques: matériau magnétostrictif, magnétoélectrique p. ex.). Parmi les capteurs piézoélectriques, on distingue ceux exploitant l'effet piézoélectrique en statique (excitation par une tension continue) et ceux utilisant l'effet piézoélectrique en dynamique (excitation fréquentielle). Parmi ces derniers, on peut distinguer plusieurs classes selon l

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https://fr.wikipedia.org/wiki/Capteur_pi%C3%A9zo%C3%A9lectrique

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Un transducteur est un dispositif convertissant un signal physique en un autre ; par exemple un signal lumineux en signal nerveux (vision animale) ou signal électrique (photorécepteur). Types

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XBAR resonators in 128° Y-cut Lithium Niobate LiNbO3

Manal Zeddoug

The increasing demand of higher frequencies technologies in RF (Radio frequency) components, especially for telecommunication, create a need to develop wider and higher frequency bands filters, with optimal performances. Thus, constant effort are made to develop new resonators that outperform excited technologies mainly in terms of electromechanical coupling and quality factor. Excited Bulk Acoustic Resonator XBAR which are composed of a single piezoelectric crystal layer, with metallic electrodes on the top surface, seem to be an interesting solution. It has indeed been shown that it can achieve higher frequency than others acoustic waves propagation technologies. The different characteristics of these resonators are mainly determined by their dimensions and the properties of the piezoelectric membrane. Lithium Niobate has shown interesting piezoelectric properties such as a high phase velocity and large electromechanical coupling which enable wider filter bandwidths. Therefore, using this material in the XBAR represents an attractive way to respond to this flourishing need. The aim of this project is thus to explore the potential of using LiNbO3 substrate with a new orientation. The case of a 128° Y-cut Lithium Niobate LiNbO3 membrane is going to be studied. For that we are first going to review the proprieties of the 128° Y-cut material and how the resonator composed of this substrate has been modeled. Finally, we will search for the combination of geometrical parameters which permits the optimal performance of the resonator.

2021

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Brachial artery waveforms for automatic blood pressure measurement

Nikolaos Stergiopulos

Theoretically the auscultatory method using Korotkoff sounds is more related to the maximum artery closure status, while the oscillometric method is more related to the overall artery closure status under the cuff. Therefore, the latter is less accurate than the former. This work introduces a new method, which is more accurate than the oscillometric method and suitable for automatic devices. To monitor the maximum artery closure status, a piezoelectric film sensor is attached to the skin just above the brachial artery and under the central section of the cuff where maximum cuff pressure is transferred to the arm. Using the waveform features obtained by this sensor, measurement errors of 0.7 +/- 2.5 and 1.27 +/- 4.53 mmHg were obtained for the systolic and diastolic pressure, respectively. These reflect small deviations from auscultatory clinical data. (C) 2012 Elsevier Ltd. All rights reserved.

Elsevier2013

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A novel fiber-interface directional waveguide coupler was inscribed on the surface of a coreless fiber by femtosecond laser, and was successfully applied to highly sensitive refractive index (RI) measurements. The primary arm was first inscribed to couple light from a lead-in single mode fiber to the fiber interface, then back to a lead-out single mode fiber. A side arm was inscribed parallel and in close proximity to the primary arm. Light propagating in the primary arm could then be efficiently coupled into the side arm when a phase-matching condition was met, which produced a dramatic spectral dip at the coupling wavelength. The proposed device achieved a sensitivity as high as similar to 8249 nm/RIU over an RI range of 1.44-1.45, due to strong evanescent fields excited in fiber-interface waveguides. The proposed in-fiber directional coupler exhibits high mechanical strength, a compact configuration, and excellent RI sensitivity. As such, it has significant potential for practical applications in biochemical sensing. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

OPTICAL SOC AMER2020

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