RT Dissertation/Thesis
T1 Engineering non-Hermitian and topological flow of sound
A1 Rosendo López, María
AB During the last decades, acoustic and phononic metamaterial research was focusedon finding new ways to modify the flow of sound waves at will. In this project,we focus on exploring novel properties of sound by developing numerical code andtheoretical methods to understand the acoustic analogy to non-Hermitian systems,topological insulators, and other exciting phenomena in condensed matter physicssuch as the magic angle in twisted bilayer graphene. Succinctly, we wish to translatethese common notions of quantum mechanics into classical acoustics to find newproperties for the case of sound.Non-Hermitian acoustic structures can be achieved by balancing acoustic loss andgain units. Commonly known as Parity-Time (PT) symmetric structures, they haveneither parity symmetry nor time-reversal symmetry, but are nevertheless symmetricin the product of both. In particular, the doctoral research project aims at designingacoustic PT symmetry and demonstrating the extraordinary scattering characteristicsof the acoustic PT medium based on exact theoretical predictions and numericalanalysis. Hence, we investigate the possibilities to realize one-way cloaks of invisibilityand broken symmetry properties with amplifying or attenuating behaviour.Topological sound combines the knowledge of topology in mathematics and electronicswith sound waves. Knowing that artificial sonic lattices have been widely usedto explore topological phases of sound and its properties, we propose to study theproperties of Second Order Topological Insulators when non-hermiticity is involved.Deriving a semi-numerical tool that allows us to compute the spectral dependenceof corner states in the presence of defects, we illustrate the limits of the topologicalresilience of the confined non-Hermitian acoustic states.An attractive motivation of these acoustic structures compared to their electroniccounterparts, is their easy fabrication and tunability, allowing the experimentalverification of this quantum analogies as well as the development of many numericalstudies. Thereby, in the last part of this thesis we mimic twisted bilayer physics in amechanical twisted bilayer configuration and also in an acoustical bilayer. Designingthe mathematical models to describe the physics involved, we show how the twistangle is related to the flat band formation as happens in twisted bilayer graphene.
YR 2022
FD 2022-07
LK https://hdl.handle.net/10016/36385
UL https://hdl.handle.net/10016/36385
LA eng
DS e-Archivo
RD 18 jul. 2024