Non-contact, single-sided access ultrasonic guided waves for the assessment of materials mechanical properties

Abstract: Research about material characterization without contact has been carried out by many authors using immersion or laser-based ultrasonic techniques. Immersion techniques however imply that the material is not water sensitive and that the sample fits within the immersion tank. Therefore, it is important to develop a characterization process that is suitable for all types of materials, and ideally not requiring access to both sides of the tested specimen, as this is often not possible in industrial context.Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

Wafer-scale detachable monocrystalline Germanium nanomembranes for the growth of III-V materials and substrate reuse

Germanium (Ge) is increasingly used as a substrate for high-performance optoelectronic, photovoltaic, and electronic devices. These devices are usually grown on thick and rigid Ge substrates manufactured by classical wafering techniques. Nanomembranes (NMs) provide an alternative to this approach while offering wafer-scale lateral dimensions, weight reduction, limitation of waste, and cost effectiveness. Herein, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process, which consists of the fabrication of wafer-scale detachable monocrystalline Ge NMs on porous Ge (PGe) and substrate reuse. We demonstrate monocrystalline Ge NMs with surface roughness below 1 nm on top of nanoengineered void layer enabling layer detachment. Furthermore, these Ge NMs exhibit compatibility with the growth of III-V materials. High-resolution transmission electron microscopy (HRTEM) characterization shows Ge NMs crystallinity and high-resolution X-ray diffraction (HRXRD) reciprocal space mapping endorses high-quality GaAs layers. Finally, we demonstrate the chemical reconditioning process of the Ge substrate, allowing its reuse, to produce multiple free-standing NMs from a single parent wafer. The PEELER process significantly reduces the consumption of Ge during the fabrication process which paves the way for a new generation of low-cost flexible optoelectronics devices.Comment: 17 pages and 6 figures along with 3 figures in supporting informatio

Vibrations non linéaires et rayonnement acoustiques de structures minces de type haut-parleur.

It has been experimentally shown that the shape and the materials of loudspeaker membranes have an influence on sound reproduction. From those observations the present thesis aims at modeling the nonlinear behavior of loudspeakers subjected to large amplitude motions over the audible bandwidth (including electrical and geometrical nonlinearities). The first part describes a theoretical approach of the influence of materials and shape on the vibration pattern of an idealized loudspeaker. The dynamic analog of the Von-Kármán equations is used and the solutions are projected over the linear modes of the structure. The second part proposes a resolution scheme of the electromechanical couplings using the state space formalism. The problem is first developed in the case of an unique mode of vibration and then extended including resonance modes and geometrical nonlinearities of the structure. In the third part, a time-domain approach of the radiation problem based on the Rayleigh integral is proposed. The method uses the Spatial Impulse Response technique which allow to reduce calculation costs directly in the time-domain. Finally, the present approach is applied in the case of a prototype developed at the LAUM by Guy Lemarquand. A good agreement between measurements and predictions using the present model can be achieved and the influence of geometrical nonlinearities on sound radiation is discussed.Si la forme et les matériaux utilisés dans la facture des membranes de haut-parleurs ont une influence notoire sur la qualité de restitution, leur étude reste majoritairement empirique. Cette thèse propose une modélisation du comportement vibratoire et acoustique de haut-parleurs en incluant les phénomènes non linéaires apparaissant en régime de grandes amplitudes. Dans la première partie, l'influence de la forme et des matériaux sur le comportement vibratoire d'une structure de haut-parleur idéalisée est étudiée de manière théorique en utilisant les analogues dynamiques des équations de Von-Kármán et une approche modale. La seconde partie propose une méthode de résolution du problème électromécanique incluant tous les types de non-linéarités connus. La formulation sous forme d'espace d'état est exprimée lorsque l'on prend en compte les modes de résonance de la structure. Dans la troisième partie, le calcul du champ de pression rayonné par une structure axisymétrique est approché par l'intégrale de Rayleigh. La résolution temporelle se fonde sur la technique de Réponses Impulsionnelles Spatiales qui permet un gain de temps de calcul important. Enfin la quatrième partie propose une analyse expérimentale sur un prototype de haut-parleur sans suspension développé au LAUM par Guy Lemarquand. Mesures et prédictions en régime linéaire et non linéaire sont comparées et l'influence des non-linéarités géométriques est discutée

Vibrations non linéaires et rayonnement acoustique de structures minces de type haut-parleur

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Development of ultrasonic thickness measurements of solidification front inside metallurgical reactors

The corrosive molten salts used for aluminum electrolysis attack the walls of the electrochemical reactors, reducing their lifetime and increasing production costs. Fortunately, a ledge is formed on those walls by the solidification of the molten salts used as the electrolytic bath, due to the heat losses through the sides of the reactors. This ledge is essential, protecting the sidewalls from the corrosive effect of the bath. Its thickness must however be controlled to avoid a reduction of the efficiency caused by a partial reduction of the electrolysis surface. One challenge is to measure the ledge thickness inside operating cells. The originality of this work resides in the development of an ultrasonic device to provide a non-intrusive ledge thickness measurement. Experimental results are obtained on a specially developed setup using the proposed ultrasonic device and are compared to ledge thicknesses obtained with an intrusive probe. The ultrasonic thickness measurement concept is validated up to 950 °C with a satisfactory accuracy inside 6 mm of the intrusive measurement

Characterization of viscoelastic moduli and thickness of isotropic, viscoelastic plates using multi-modal Lamb waves

This paper presents an approach exploiting the sensitivity of Lamb waves for characterizing the viscoelastic moduli and thickness of plates. The analytical sensitivity functions are first derived in the case of an isotropic plate and are integrated into an iterative inverse problem to optimize its viscoelastic moduli and thickness based on a zero-finding approach (Gauss–Newton algorithm for a multivariable problem). This method is validated numerically for a viscoelastic plate and shows high accuracy and low computational cost when compared to existing methods. Experimental validation demonstrates the ability of the algorithm to assess simultaneously the viscoelastic moduli and the thickness of isotropic plate-like structures

Optimization of virtual sources distribution in 3D echography

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