Woodruff School of Mechanical Engineering

Faculty Candidate Seminar


Time-Asymmetric Acoustic Metamaterials for Manipulating Sound in Unprecedented Ways


Mr. Romain Fleury


Department of Electrical and Computer Engineering, The University of Texas at Austin


Monday, February 23, 2015 at 11:00:00 AM


MRDC Building, Room 4211


Dr. Alper Erturk and Dr. Karim Sabra


Metamaterials are artificial structures with anomalous wave interaction capabilities, which are associated with unconventional physical phenomena, such as negative refraction or cloaking. In this talk, I will discuss the unusual acoustic properties of metamaterials and metasurfaces that are not invariant upon time-reversal. First, I will show how time-reversal symmetry breaking can be exploited to break Rayleigh reciprocity, leading to a novel class of non-reciprocal acoustic devices, such as isolators and circulators. Several design examples with promising industrial potential will be discussed, along with experimental results. I will then use them as building blocks to construct the acoustic equivalent of topological insulators, a metamaterial that supports one-way phononic transport on its edges with strong topological protection against defects. Second, I will study the largely uncharted scattering properties of time-asymmetric acoustic systems that are engineered to be invariant under a special kind of space-time symmetry, consisting in taking their mirror image and running time backwards. Known as Parity-Time (PT) symmetry, this property leads to exceptional scattering behaviors such as unidirectional invisibility and phase compensation. I will present an experimental validation of these effects and demonstrate how PT-symmetric metasurface pairs can replicate physical phenomena usually associated with bulk metamaterials, like negative refraction, planar focusing and cloaking, with the clear advantage of being completely loss-immune and potentially broadband.


Romain Fleury is currently a Ph.D. candidate in the department of Electrical and Computer Engineering at The University of Texas at Austin, where he is working with Professor Andrea Alý on new interdisciplinary concepts in wave physics and engineering, with an emphasis on acoustic metamaterials and metasurfaces. He received the M.S. in Engineering from Ecole Centrale de Lille, France, and the M.S. in Micro and Nanotechnologies from the University of Lille, France, in 2010. During his Ph.D., he has published over 20 articles in peer-reviewed scientific journals, including 15 first-author papers in journals such as Science, Physical Review Letters, and Nature Communications. His work on Non-Reciprocal Acoustics was featured on the cover of Science, and attracted the attention of the general public, with appearances in various media including NBC News, Daily Mail, and Scientific American. In 2014, he received the Best Student Paper award in Engineering Acoustics as well as the Young Presenter Award in Noise from the Acoustical Society of America. His research on Parity-Time symmetric Acoustics has been awarded Best Student Paper at the International Congress Metamaterials 2014, the premier conference in the field.


Refreshments will be served.