Contrôle par ultrasons

Résumé

Le contrôle par ultrasons est une méthode de contrôle non destructif permettant la détection de défaut à l'intérieur d'un matériau. Le contrôle par ultrasons est basé sur la transmission et la réflexion d'onde de type ultrasons à l'intérieur d'un matériau. Les ondes utilisées peuvent être libres (de compression ou de cisaillement) ou guidées (de surface ou de plaque). Principe Une onde ultrasonore est émise par un transducteur placé sur la surface du matériau à contrôler et se propage dans le matériau. Il existe des méthodes par contact (le palpeur est en contact avec la pièce) ou par immersion (la pièce et le palpeur sont immergés dans de l'eau). Dans le cas de la méthode par contact, il est nécessaire d'ajouter un couplant (eau ou gel) entre le palpeur et la pièce pour assurer la transmission des ondes. Lorsque ces ultrasons rencontrent une interface délimitant deux milieux ayant des impédances acoustiques différentes, il y a réflexion. Les ultrasons réfléchis sont ca

Source officielle

https://fr.wikipedia.org/wiki/Contr%C3%B4le_par_ultrasons

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Acoustophoretic Synchronization of Mammalian Cells in Microchannels

Jonathan David Adams, Herbert Shea

We report the first use of ultrasonic standing waves to achieve cell cycle phase synchronization in mammalian cells in a high-throughput and reagent-free manner. The acoustophoretic cell synchronization (ACS) device utilizes volume-dependent acoustic radiation force within a microchannel to selectively purify target cells of desired phase from an asynchronous mixture based on cell cycle dependent fluctuations in size. We show that ultrasonic separation allows for gentle, scalable, and label-free synchronization with high G1 phase synchrony (∼84%) and throughput (3 × 106 cells/h per microchannel).

American Chemical Society2010

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The in-plane component of the wavefield provides valuable information about media properties from seismology to nondestructive testing. A new compact scanning laser ultrasonic interferometer collects light scattered away from the angle of incidence to provide the absolute ultrasonic displacement for both the out-of-plane and an in-plane components. This new system is tested by measuring the radial and vertical polarization of a Rayleigh wave in an aluminum half-space. The estimated amplitude ratio of the horizontal and vertical displacement agrees well with the theoretical value. The phase difference exhibits a small bias between the two components due to a slightly different frequency response between the two processing channels of the prototype electronic circuitry. © 2010 American Institute of Physics.

American Institute of Physics2010

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Piezoelectric acoustic sensors and ultrasonic transducers based on textured PZT thin films

Nicolas Ledermann

This work dealt with the establishment of a reproducible and industrially exploitable fabrication technology for piezoelectric MEMS based on PZT thin films. {100}-textured piezoelectric 1-4 μm thick films were found to be the most suited materials for MEMS applications where a strong transverse e31,f coefficient is required. Values of 11.5 to 12.5 C/m2 throughout the investigated thickness range have been obtained. PZT MEMS requires some special microfabrication processes. The patterning of platinum electrodes in ICP reactor with an Ar/Cl2 gas mixture gave satisfying results. For 1 μm PZT films, excellent results were achieved with dry etching in an ECR/RF low-pressure reactor. Above 1 μm thickness, wet etching technique was used. The chosen process flow was such that all layers up the top electrode were first deposited, and then sequentially patterned. In this way, the functional properties were completely maintained. Finally, the process flow related to PZT was successfully combined with deep silicon etching techniques to produce free standing structures. The applicability of the processes has been demonstrated by means of two piezoelectric micro-electro-mechanical devices. First, a cantilever acoustic sensor for low frequency applications (< 50 Hz) has been developed for integration in photoacoustic gas detectors. A high device sensitivity of up to 150 mV/Pa has been obtained with noise level corresponding to a few mPa, mainly due to the preamplifier. The second device was based on a silicon/PZT diaphragm to produce a vibrating structure in view of fabricating ultrasonic transducers for position sensors and non-destructive testing probes. The study of the basic properties of such structures has shown excellent results as coupling factors k2 up to 5% for PZT 2 μm / Si 4 μm SOI membranes held with four small bridges. Ultrasonic wave transmission between two devices has been achieved up to a distance of 200 mm. The microfabrication of piezoelectric MEMS was found to be a complex task where all aspects from materials, microfabrication, and device design to assessment of performance are closely interconnected. Piezoelectric MEMS can offer exciting opportunities to fabricate innovative and performing devices.

EPFL2003

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Piezoelectric acoustic sensors and ultrasonic transducers based on textured PZT thin films

Nicolas Ledermann

EPFL2003