Surface Green's function of a piezoelectric half-space

International audienceThe computation of the two-dimensional harmonic spatial-domain Green's function at the surface of a piezoelectric half-space is discussed. Starting from the known form of the Green's function expressed in the spectral domain, the singular contributions are isolated and treated separately. It is found that the surface acoustic wave contributions, i.e. poles in the spectral Green's function, give rise to an anisotropic generalization of the Hankel function $H_0^{(2)}$, the spatial Green's function for the scalar two-dimensional wave equation. The asymptotic behavior at infinity and at the origin (for the electrostatic contribution) are also explicitely treated. The remaining non-singular part of the spectral Green's function is obtained numerically by a combination of fast Fourier transform and quadrature. Illustrations are given in the case of a substrate of Y-cut lithium niobate

Theoretical analysis of damping effects of guided elastic waves at solid/fluid interfaces

International audienceA theoretical description of ideal and viscous fluid media is proposed to address the problem of modeling damping effects of surface acoustic waves and more generally of any guided elastic waves at the interface between viscous fluids and solids. It is based on the Fahmy-Adler eigenvalue representation of the elastic propagation problem, adapted to provide Green's function of the considered media. It takes advantage of previous efforts developed to numerically stabilize Green's-function computation process. This function is used to compute a harmonic admittance according to the Blötekjaër approach. The influence of acoustic radiation and viscosity effects on different kinds of waves excited on various substrates is reported and discussed

Fast contactless vibrating structure characterization using real time field programmable gate array-based digital signal processing: Demonstrations with a passive wireless acoustic delay line probe and vision

International audienceVibrating mechanical structure characterization is demonstrated using contactless techniques best suited for mobile and rotating equipments. Fast measurement rates are achieved using Field Programmable Gate Array (FPGA) devices as real-time digital signal processors. Two kinds of algorithms are implemented on FPGA and experimentally validated in the case of the vibrating tuning fork. A first application concerns in-plane displacement detection by vision with sampling rates above 10 kHz, thus reaching frequency ranges above the audio range. A second demonstration concerns pulsed-RADAR cooperative target phase detection and is applied to radiofrequency acoustic transducers used as passive wireless strain gauges. In this case, the 250 ksamples/s refresh rate achieved is only limited by the acoustic sensor design but not by the detection bandwidth. These realizations illustrate the efficiency, interest, and potentialities of FPGA-based real-time digital signal processing for the contactless interrogation of passive embedded probes with high refresh rates

High overtone Bulk Acoustic Resonators: application to resonators, filters and sensors

International audienceAcoustelectric devices have been used now for several decade to stabilize oscillators, to filter radio-frequency signals or to allow for physical and even chemical detection and measures.Among all the structures that have been developed in that purpose, one has been revealing particularly interesting for the development of high quality factor resonator on an extended range of frequency. It is based on the generation of high overtones in bulk acoustic wave resonant structure and therefore are currently called HBARs. These devices may be fabricated along various approaches but they always consist of a thin (or thinned) piezoelectric layer deposited or bonded onto a high quality single crystal material. The spectral response of this kind of device exhibit a periodic comb of peaks modulated by the transducer response, yielding resonances on a very large spectrum with various characteristics and properties. We present here the basic principles of such devices, their remarquable properties, the etchnologies required to manufacture them and the various applications they can be applied for. A focus is partcularly dedicated to oscillator stabilization and to wirelss sensor development

Simulation of 3D periodic piezoelectric transducers radiating in layered media using Finite Element/Boundary element Analysis

Abstract. This paper is devoted to the description of a mixed finite element/boundary element analysis for the simulation of any periodic transducer radiating in any combination of solid and fluids assuming flat interfaces and linear operation regime. The theoretical developments required in that purpose are described and different examples of transducers are considered to demonstrate the interest of the proposed approach. 1

Sensibilite des oscillateurs a quartz a ondes de surface aux contraintes et gradients thermiques

SIGLEINIST T 77066 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Chronologie holocène des dépôts de mise en place catastrophique dans une haute vallée alpine. Le cas du comblement de l'ombilic du tour (Alpes françaises du Nord) [ Brutal genesis deposits holocene chronology in a high alpine valley : the case of the filling-up of the tour ombilic.]

The high catchment of the Arve river (upper valley of Chamonix, French Alps) offers a great variety of deposits due to catastrophe. These deposits start during Boreal period with a phase of torrential spasmody activity. The Ancient Atlantic period is marked by the brutal «opening» of the «combe de la Vormaine» catchment, which generates a big upheaveal of the morphogenesis. A contrario, there is a cutting- down phase during the Subboreal period. In the Subatlantic period, and more particularly during the Little Ice Age, a recrudescence of torrentiality in relation with a phase of intense solifluxion on the slopes can be observed. The present dynamic of the river Arve, not very developped during the Holocene period, is the consequence of the recent activation of a slide of great importance on the slope of the Posettes.Le haut bassin-versant de l'Arve présente une grande variété de dépôts de mise en place catastrophique. Ils débutent au Boréal, avec une phase d'activité torrentielle spasmodique. L'Atlantique ancien est marqué par l' « ouverture » brutale de la «Combe» de la Vormaine qui engendre de grands bouleversements dans la morphogenèse. Après une phase d'incision durant le Subboréal, le Subatlantique, et plus particulièrement le Petit Age Glaciaire, voient une recrudescence de la torrentialité en relation avec une phase de solifluxion intense sur les versants. La dynamique torrentielle stries, actuelle de l'Arve, peu développée pendant l'Holocène, est la conséquence de l'activation récente d'un mouvement de terrain de grande ampleur sur le versant des Posettes.Ballandras Stephane, Jaillet Sylvain. Chronologie holocène des dépôts de mise en place catastrophique dans une haute vallée alpine. Le cas du comblement de l'ombilic du tour (Alpes françaises du Nord) [ Brutal genesis deposits holocene chronology in a high alpine valley : the case of the filling-up of the tour ombilic.]. In: Quaternaire, vol. 7, n°2-3, 1996. pp. 85-96

La transition Tardiglaciaire/Holocène à travers les fluctuations du glacier du Tour (Vallée de Chamonix, Alpes du Nord françaises) [Lateglacial/Holocene transition through glacier du Tour fluctuations (upper Chamonix valley, French Alps)]

Below the glacier du Tour and the moraines settled during the Little Ice Age, four frontal moraine systems can be seen ; only the last three of them extends out of the Tour ombilic. The 9935 ± 200 ¹⁴C BP datation of the youngest of them allows to confer these three moraines to the Younger Dryas and to propose this datation as Lateglacial terminus post quem. The setting down of the last one — Tour stadial — takes place between 9935 ± 200 BP and 8414 ± 50 BP. Several hypothesis are presented to set precisely this stadial at circa 9000 BP.En contrebas du glacier du Tour, on remarque quatre ensembles morainiques se situant à l'aval des moraines mises en place lors du Petit Age Glaciaire. Seuls les trois plus externes débordent de l'ombilic du Tour. La datation de ¹⁴C 9935 ± 200 BP, obtenue pour le plus interne d'entre eux, permet d'attribuer ces trois vallums au Dryas récent et de proposer cette datation comme terminus post quem du Tardiglaciaire. La mise en place du plus interne - stade du Tour - est comprise entre 9935 ± 200 et 8414 ±50 ¹⁴C BP. Un ensemble d'hypothèses est avancé afin de caler plus précisément ce stade vers 9000 BP (transition Préboréal-Boréal).Jaillet Sylvain, Ballandras Stephane. La transition Tardiglaciaire/Holocène à travers les fluctuations du glacier du Tour (Vallée de Chamonix, Alpes du Nord françaises) [Lateglacial/Holocene transition through glacier du Tour fluctuations (upper Chamonix valley, French Alps)]. In: Quaternaire, vol. 10, n°1, 1999. pp. 15-23