Devant les difficultes rencontrees pour l'exploration de surfaces complexes, en particulier dans l'industrie nucleaire, le traducteur ultrasonore multielements conformable permet un controle non destructif de pieces a geometrie complexe 3D. Ce type de capteur est un reseau matriciel compose d'emetteurs independants moules dans une resine mecaniquement souple. Une analyse vibratoire par elements finis permet de definir la structure emettrice en piezocomposite 1-3, ce qui conduit a l'elaboration d'elements emetteurs. L'etude experimentale de ces dispositifs a mene au developpement du modele semi-analytique, pour prendre en compte les contraintes tangentielles calculees a l'interface entre l'emetteur et le milieu de propagation, par elements finis. Ceci permet de visualiser quelques phenomenes lies au couplant fluide et ameliore la prediction du champ en ondes transverses. De la, un prototype du reseau conformable a ete caracterise en transmission et en echographie.

https://tel.archives-ouvertes.fr/tel-00474393/document

Contribution au développement et à la modélisation d'un traducteur ultrasonore multiéléments conformable pour l'inspection au contact de composants à géométrie complexe 3D

Interface acoustic waves with predominantly longitudinal elastic displacements in continuous materials of lithium niobate and lithium tantalate are reported. The interface is represented by the electrically conducting layer or periodic sequence of metal electrodes. The interface effective permittivity function shows a pronounced resonant behavior in YZ cuts of LN and LT at slowness values slightly higher the point, where longitudinal bulk wave propagates in continuous material. The periodic admittance characteristics are calculated for the metal electrode thickness to wavelength ratios in the range from 0.1 to 10%. The periodic admittance in YZ cut of LT shows a resonant behavior for quite small thickness to wavelength ratios in the range of 0.2 to 1% at the metallization ratio of 0.5. In YZ cut of LN the periodic admittance shows a resonance in the whole range of calculated electrode thicknesses. The propagation velocity determined by resonant frequency approximates the value of 7100 m/s. The relative bandwidth between resonance and anti resonance tends to be wider in the range from 0.33 to 1.43 % with increasing electrode thickness, while the resonant quality factor varies from 1600 to 220. The calculated temperature coefficient of frequency for all calculated values of metal thicknesses in YZ cut of LN does not exceed -33 ppm.

P3I-6 Interface Leaky Longitudinal Waves in Lithium Niobate and Lithium Tantalate

The purpose of the paper is to outline a systematic and unified non-local treat-
ment of mode conversion effects associated with an interface superlattice being a 2D
pseudo-array composed of altered phase inclusions (exemplified by impurity clusters)
and located at a solid-solid plane interface. It will be illustrated, in some detail, for
the instructive case of a Stoneley type acoustic wave (SW), incident on a period-
ically nonhomogeneous portion of an interface and partly transformed into bulk
modes propagating in one of the component solid. An analytical model scheme is
constructed, using a variational method combined with the T matrix approach, ap-
propriate for the 2D periodic array treated, and decaying into the depth of this solid
for the structure in a way determined by the array geometry and element 3D pro-
files as well as the boundary conditions at the interface. An apodization (weighting)
to reduce the side-lobes level is incorporated into the structure by appropriately
varying lateral dimensions and the depth of particular scatterers.

/pdf/elastic-wave-behaviour-in-2-d-acoustic-interface-4yg7fxpwaj.pdf

R.O. Claus

Papers

Effects of Surface Bonding on the Existence of Ultrasonic Stoneley Waves