Nouveaux concepts pour l’imagerie et la détection (NCIS)

Coordinateurs

Julien DE ROSNY

Tél. : 01 80 96 30 52

Claire PRADA

Tél. : 01 80 96 30 53

Actualités

Viscoelastic dynamics of a soft strip subject to a large deformation Delory, A., D. A. Kiefer, M. Lanoy, A. Eddi, Prada C., and F. Lemoult Soft Matter (2024) Résumé: To produce sounds, we adjust the tension of our vocal folds to shape their properties and control the pitch. This efficient mechanism offers inspiration for designing reconfigurable materials and adaptable soft robots. However, understanding how flexible structures respond to a significant static strain is not straightforward. This complexity also limits the precision of medical imaging when applied to tensioned organs like muscles, tendons, ligaments and blood vessels among others. In this article, we experimentally and theoretically explore the dynamics of a soft strip subject to a substantial static extension, up to 180%. Our observations reveal a few intriguing effects, such as the resilience of certain vibrational modes to a static deformation. These observations are supported by a model based on the incremental displacement theory. This has promising practical implications for characterizing soft materials but also for scenarios where external actions can be used to tune properties.
Beating resonance patterns and extreme power flux skewing in anisotropic elastic plates Kiefer, D. A., S. Mezil, and C. Prada Science advances 9, no. 51, eadk6846 (2023) Résumé: Elastic waves in anisotropic media can exhibit a power flux that is not collinear with the wave vector. This has notable consequences for waves guided in a plate. Through laser-ultrasonic experiments, we evidence remarkable phenomena due to slow waves in a single-crystal silicon wafer. Waves exhibiting power flux orthogonal to their wave vector are identified. A pulsed line source that excites these waves reveals a wave packet radiated parallel to the line. Furthermore, there exist precisely eight plane waves with zero power flux. These so-called zero-group-velocity modes are oriented along the crystal's principal axes. Time acts as a filter in the wave-vector domain that selects these modes. Thus, a point source leads to beating resonance patterns with moving nodal curves on the surface of the infinite plate. We observe this pattern as it emerges naturally after a pulsed excitation.
Decomposition of acousto-elastic matrices for contactless modal analysis and vibration shaping Palerm, C., C. Prada, B. Gerardin, A. Talon, and J. De Rosny Journal of Sound and Vibration 571 (2024) Résumé: A contactless method based on acousto-elastic transmission matrix analysis is proposed to recover the modal properties of weakly damped mechanical structures. The matrix is acquired using eight loudspeakers and a laser vibrometer probing hundreds of points. The matrix analysis is particularly interesting in case of overlapping modes. The proposed measurement set-up and associated data processing using the Singular Value Decomposition are applied to two symmetric samples, a gear and two monobloc impellers. Further analysis are performed taking advantage of their particular modal behavior, common to many rotationally symmetric structures. The method also enables to clearly identify the effect of damages on the modal organization. Additionally, the setup can also be used to excite specific patterns on the elastic structures. Finally, the acousto-elastic results are compared to the ones obtained with a classical impact hammer and high resolution algorithms.
Piezo-orbital backaction force in a rare-earth-doped crystal Louchet-Chauvet, A., P. Verlot, J. P. Poizat, and T. Chanelière Physical Review Applied 20, no. 5 (2023) Résumé: We investigate a system composed of an ensemble of room-temperature rare-earth ions embedded in a bulk crystal, intrinsically coupled to internal strain via their sensitivity to the surrounding crystal field. We evidence the generation of a mechanical response under resonant atomic excitation. We find this motion to be the sum of two fundamental, resonant optomechanical backaction processes: a conservative, piezo-orbital mechanism, resulting from the modification of the crystal field associated with the promotion of the ions to their excited state, and a dissipative, nonradiative photothermal process related to the phonons generated throughout the atomic population relaxation. Our work expands the horizons of research in hybrid optomechanics, and unveils unexplored interactions that may be key for understanding the dephasing dynamics of ultracoherent rare-earth ions.

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Présentation du thème

Les recherches menées au sein de ce thème sont tournées vers les applications, elles reposent sur une alliance de compétences variées en physique des ondes, traitement de signal et instrumentation et se nourrissent principalement des travaux menés dans le thème ondes en milieux complexes. L’idée est d’exploiter la diversité temporelle et/ou spatiale des ondes pour développer de nouvelles méthodes de détection et d’imagerie dans des contextes applicatifs variés allant de l’imagerie biologique au contrôle non destructif. Ces méthodes sont implémentées pour différents types d’ondes, acoustiques, élastiques et optique et sont souvent multi-ondes (ultrasons laser, acousto-optique, élasto-acoustique). Elles reposent sur des principes physiques tels que la réciprocité, l’invariance par retournement temporel, l’émergence des fonctions de Green par corrélation de bruit et exploitent les technologies de réseaux multiéléments : réseaux de microphones ou de transducteurs piézo-électriques, réseaux d’antennes, capteurs CCD, modulateurs spatiaux de lumière.

Le thème est structuré en quatre axes : l’imagerie optique plein champ, l’acousto-optique en milieu diffusant, les méthodes multi-éléments en acoustique et les ondes élastiques guidées appliquées à l’évaluation des matériaux.