[Caustique en « corne de croissant » et focalisation des ondes acoustiques générées par une antenne paramétrique]
Ce travail est consacré à l'étude de la caustique en « corne de croissant » à la surface d'un réflecteur hémi-cylindrique illuminée par des ondes planes. En vue de générer des ondes planes acoustiques de basse fréquence (autour de 4 kHz), une antenne paramétrique disponible commercialement a été utilisée. Elle produit une onde ultrasonore porteuse de forte puissance à 40 kHz qui peut-être modulée en amplitude de façon électronique entre 200 Hz et 10 kHz. Le processus d'auto-démodulation au cours de la propagation dans l'air permet de générer un champ acoustique ultra-directif (c'est-à-dire des ondes quasi-planes) autorisant une étude précise de la focalisation le long de la caustique. Le coefficient de focalisation est alors calculé localement, en utilisant deux approches numériques différentes, d'une part en calculant la densité de rayons tangents à la caustique et d'autre part en mettant en œuvre une méthode de calcul du type tracé de rayons. Des résultats expérimentaux préliminaires sont alors décrits avec l'objectif de valider les prédictions numériques (position spatiale de la singularité et coefficient de focalisation).
The present Note is devoted to the study of the so-called cuspidal caustic at the surface of a hemi-cylindrical reflector illuminated with plane waves. In order to generate low frequency (e.g. in the range of 4 kHz) acoustical plane waves, a commercially available parametric array has been used. It produces powerful ultrasonic carrier waves at 40 kHz which can be electronically modulated between 200 Hz and 10 kHz. Further self-demodulation process during propagation in air generates an ultra-directive acoustical field (i.e. quasi-planar wavefronts) enabling to accurately study the focusing process occurring along the cuspidal caustic. The focusing coefficient can be computed locally by using two numerical tools, on one hand by computing the density of tangent rays to the caustic, and on the other hand by using some numerical results provided by a ray tracing algorithm. Some preliminary experimental data are then provided in order to validate the numerical predictions (spatial position of the caustic and focusing coefficient).
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Publié le :
Mot clés : Acoustique, Propagation sur un réflecteur hémi-cylindrique, Caustique en corne de croissant, Coefficient de focalisation, Calcul du type tracé de rayons
Bernard Castagnède 1 ; Sohbi Sahraoui 1 ; Vincent Tournat 1 ; Najat Tahani 1
@article{CRMECA_2009__337_9-10_693_0,
author = {Bernard Castagn\`ede and Sohbi Sahraoui and Vincent Tournat and Najat Tahani},
title = {Cuspidal caustic and focusing of acoustical waves generated by a parametric array onto a concave reflecting surface},
journal = {Comptes Rendus. M\'ecanique},
pages = {693--702},
publisher = {Elsevier},
volume = {337},
number = {9-10},
year = {2009},
doi = {10.1016/j.crme.2009.09.006},
language = {en},
}
TY - JOUR AU - Bernard Castagnède AU - Sohbi Sahraoui AU - Vincent Tournat AU - Najat Tahani TI - Cuspidal caustic and focusing of acoustical waves generated by a parametric array onto a concave reflecting surface JO - Comptes Rendus. Mécanique PY - 2009 SP - 693 EP - 702 VL - 337 IS - 9-10 PB - Elsevier DO - 10.1016/j.crme.2009.09.006 LA - en ID - CRMECA_2009__337_9-10_693_0 ER -
%0 Journal Article %A Bernard Castagnède %A Sohbi Sahraoui %A Vincent Tournat %A Najat Tahani %T Cuspidal caustic and focusing of acoustical waves generated by a parametric array onto a concave reflecting surface %J Comptes Rendus. Mécanique %D 2009 %P 693-702 %V 337 %N 9-10 %I Elsevier %R 10.1016/j.crme.2009.09.006 %G en %F CRMECA_2009__337_9-10_693_0
Bernard Castagnède; Sohbi Sahraoui; Vincent Tournat; Najat Tahani. Cuspidal caustic and focusing of acoustical waves generated by a parametric array onto a concave reflecting surface. Comptes Rendus. Mécanique, Volume 337 (2009) no. 9-10, pp. 693-702. doi : 10.1016/j.crme.2009.09.006. https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.1016/j.crme.2009.09.006/
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