Thesis defence : Gabriel Regnault

On The November 22, 2021

at 2:00 PM
Ecole Centrale de Lyon, en amphi 201, bâtiment W1

Behaviour of a pair of micrometric bubbles under ultrasonic excitation

Abstract :

Gas microbubbles are physical agents that allow a redistribution of ultrasound energy in their vicinity. In medical or industrial applications, they allow, among other things, the permeabilisation of cell membranes, the cleaning of surfaces, the optimisation of chemical reactions, etc. These bubbles are generally found in the form of more or less dense clusters. The behaviour of these groups, or clouds, of bubbles is driven by different interactions, acoustic or fluidic. To understand a cloud of bubbles, it is necessary to first study a pair of bubbles, considered as an elementary brick of this cloud. The work presented in this thesis aims to study the acoustic and fluidic couplings governing the behaviour of a pair of bubbles.

First, the behaviour of a single bubble is studied. Under certain conditions of size and acoustic pressure, its interface can oscillate in non-spherical modes. Such deformations allow the development of a slow and localised flow around the bubbles: microstreaming. A new theoretical approach, confronted with experimental data, shows that the patterns of the induced flow vary according to the predominant modal interaction, and can allow a localised action (lobe patterns confined around the bubble) or a larger scale (cross patterns).

In a second step, the analysis is extended to a bubble pair. For this purpose, an original experimental device is proposed, in order to trap two bubbles at a controlled distance, far from any boundary, in a bi-frequency resonant acoustic chamber. This device makes it possible to quantify the secondary radiation force to which the bubbles are subjected, their spherical and non-spherical deformations, the acoustic coupling at the ultrasonic scale and the induced flows. The work presented here shows the influence of non-spherical oscillations on the secondary radiation force and the possible inversion of this force for small inter-bubble distances. For a given excitation frequency, the acoustic coupling is constructive or destructive if the two bubbles of the pair are respectively under-resonant or over-resonant. Non-spherical oscillations only cause significant coupling when the two bubbles are almost in contact. In contrast, the associated flows can interact on a larger scale. A quantification of the stresses generated in the medium by these flows is carried out, and seem sufficient to induce the temporary opening of biological membranes.

Jury composition
- Philippe Marmottant, Directeur de Recherche CNRS, CNRS-Université Grenoble Alpes, rapporteur.
- Michaël Baudoin, Professeur des Universités, Université Lille, rapporteur.
- Caroline Derec, Maître de Conférences, Université Paris 7 Diderot, examinatrice.
- Philippe Blanc-Benon, Directeur de Recherche CNRS, École Centrale de Lyon, directeur de thèse.
- Cyril Mauger, Maître de Conférences, INSA de Lyon, co-encadrant.
- Claude Inserra, Maître de Conférences, Université Claude Bernard Lyon 1, co-encadrant.