CMIP Seminar: Controlling waves in complex media: from time reversal to wave front shaping via metamaterials

Tuesday, November 29, 2016

10:00–11:00 AM
Schiciano Auditorium Side A


Geoffroy Lerosey
Research Scientist
CNRS, Institut Langevin

In this talk I will discuss how waves can be controlled in complex media for imaging, communication or energy deposition purposes. After a brief introduction on waves in complex media, I will start by describing the concept of time reversal, a technique first developed in acoustics by Mathias Fink and later on transposed to the electromagnetic domain during my PhD. Particularly, I will explain the notion of spatial and temporal degrees of freedom offered by complex media, which are as many levers one can use to manipulate waves using arrays of sources. This will allow me to review experimental works we have performed in the microwave and acoustic domains, which prove that it is possible to beat the diffraction limit from the far field using time reversal in a special subset of complex media: metamaterials. I will then show how these works have pushed us to revisit the physics of metamaterials made out of resonant unit cells, and to consider and use them as deep subwavelength photonic or phononic crystals that can be locally or globally tailored, rather than as homogeneous materials. Various outcomes will be discussed, including deep subwavelength cavities and waveguides, simple negative index media, or topological metamaterial crystals. Finally I will rapidly introduce the idea of wave front shaping originally proposed in the optical domain to reproduce the results obtained using time reversal at lower frequencies. This will lead me to show how, using the knowledge acquired throughout the previous works, we have proposed to move from an active control of microwaves in complex media to a passive one, using electronically reconfigurable metasurfaces as spatial microwave modulators. Applications related to wireless communications, reconfigurable cavities, energy harvesting, radar and imaging will be briefly discussed.

Geoffroy Lerosey was born in 1979 in Avignon, France. He received a Master’s degree in engineering specialized in physics and chemistry from ESPCI ParisTech and a Master’s degree in electromagnetics and electronics from University Pierre and Marie Curie in 2003. Then he studied during his PhD under the supervision of Professor Mathias Fink, on the subject of “time reversal of electromagnetic waves and its application to wireless communications”, and received his PhD degree from University Denis Diderot in 2006. He spent a year as a postdoctoral researcher at Professor Xiang Zhang’s laboratory at University of California at Berkeley, CA, USA, working in the field of metamaterials and plasmonics. He came back in 2008 and was appointed as a research scientist by CNRS at Institut Langevin, created by Mathias Fink and now directed by Arnaud Tourin. His research interests cover the areas of wave front shaping and time reversal in complex, multiple scattering or reverberating media, from acoustics to optics, that of composite media such as photonic and phononic crystals or electromagnetic and acoustic metamaterials, and the concepts of imaging and focusing waves below the diffraction barrier. He is the author of 50 publications in internationally renowned journals, is the inventor of 12 patents, and has been invited 40 times for international conferences and seminars worldwide.