Nicolas LAFORGE : "Topological phononic crystal waveguides"

 PhD works of Nicolas LAFORGE : "Topological phononic crystal waveguides"

Abstract : Metamaterials are materials designed by man with static or dynamic properties inaccessible to natural materials. Among them, phononic crystals consist of a periodic assembly of two or more materials, and are mainly used for the design of waveguiding and filtering devices. During the past decade, a new mechanism allowing waveguiding started to be used. It is based on topology, more precisely on the creation of an interface resulting from the juxtaposition of two crystals with chiral symmetry properties. While this mechanism has proven its effectiveness in a large number of applications, it has never been used in a highly dispersive medium, or for a crystal having a geometry not similar to that of graphene. The objective of this thesis is to design such topological phononic crystals. First, we designed a phononic crystal exhibiting topological behavior for surface water waves by using a geometry exhibiting the same topological behavior as for acoustic waves in air. This similarity is allowed by the form of the equations governing these two domains, which allows us to transpose topological behaviors from one physical domain to another. We then designed a topological phononic crystal that did not rely on the geometry of graphene, still for surface water waves. This geometry allows for the design of a three-way wave splitter device. While we have demonstrated the topological behavior of this crystal, we have not confirmed the possibility of splitting a wave in three directions. Using such a geometry, but for underwater acoustic waves, we highlighted the possibility of separating a wave in three directions. This observation paves the way for the design of new waveguiding circuits.

Jury Composition :
M. Vincent LAUDE Directeur de Recherche, Université Bourgogne Franche-Comté, PhD Director
M. Muamer KADIC Maître de Conférences, Université Bourgogne Franche-Comté, PhD Co-Director
M. Yan PENNEC Professeur des Universités, Université de Lille, Reporter
M. Vincent PAGNEUX Directeur de Recherche, Le Mans Université, Reporter
Mme. Thérèse LEBLOIS Professeur des Universités, Université Bourgogne Franche-Comté, Reviewer
M. Romain FLEURY Professeur Associé, École Polytechnique Fédérale de Lausanne, Reviewer
M. Sébastien GUENNEAU Directeur de Recherche, Imperial College of London, Reviewer
M. Pierre DELPLACE Chargé de Recherche, Université de Lyon, Reviewer

Localization : Amphithéâtre J.J Gagnepain, FEMTO-ST, 15B, Avenue des Montboucons - 25000 Besançon