Description du sujet de thèse

Project Context
Acoustic and elastic waves are ubiquitous in our life, from the propagation of sound in air (which allows us to communicate) to micro-electromechanical systems (MEMS) for sensing applications, to large-scale catastrophic events, such as earthquakes and tsunamis. Although the full control of wave propagation is not possible yet, recent developments of the Solid State of Physics has proposed a new class of composite materials, generally referred as phononic crystals (PCs) and metamaterials (MMs), capable of unconventional dynamic behaviors (negative refraction, wave focusing, cloaking, …).
PCs and MMs are periodic (or quasi-periodic) composites made of building blocks, i.e., unit cells, capable of performing spatial and spectral control of waves due to frequency-dependent directionality or band gap (BG) effects (i.e., frequency regions where the propagation of waves is strongly attenuated) induced by nondestructive interferences created by either the scattered wave field from periodic abrupt stiffness / mass changes (Bragg BGs) or resonating inhomogeneities (locally resonant BGs). The concept of BG naturally implies applications involving vibrations, wave filtering and attenuation, which could be exploited in various frequency regimes ranging from Hz to kHz: reduction of ground motion of seismic (surface) waves, acoustic or underwater noise reduction, and reduction of vibrations, to cite a few.

Objectives of the thesis
The main objective of this PhD thesis is to design new metamaterial-based barriers to reduce the propagation of elastic and acoustic waves. Both the cases of airborne and underwater wave propagation will be explored with the idea of adapting, when possible, some of the airborne acoustics metamaterial concepts to the underwater context, tackling problems deriving from the (heavy) fluid-structure interactions (which invalidate some of the airborne acoustics assumptions).
The optimization of the performances by introducing new (possibly topologically protected) interfaces for the conversion and guiding of waves will also be explored.
Due to the scalable nature of wave equations, potential applications in other domains will be explored.

Contexte de travail

Location: The Institute of Electronic, Microelectronic and Nanotechnology (UMR CNRS 8520 – https://www.iemn.fr/en/) is in Villeneuve D'Ascq, close to the city of Lille (France). With a total staff of over 500 people, the institute has a broad area of research activity ranging from physics to materials science, acoustics, micro- and nanotechnology.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.