IAS Distinguished Lecture

Complexity and Time-Reversed Waves: From Metamaterial to Medicine


Time-reversal invariance is a very fundamental concept in classical and quantum physics. The objective of this talk is to show how this concept can be used to control waves in complex media and be turned into a huge source of innovations.

It was first in the field of acoustics and later for microwaves, where reversible antenna array technology was available, that “time-reversal mirrors” have been built. Such mirrors allow to refocus in space and time an incident wave field at the original source location regardless of the complexity of the propagation medium. Contrary to intuition, a remarkable property was shown: the more complex the propagation medium, the sharper the focus. Such results have been extended to focus on spots much smaller than the wavelength using new types of metamaterials, opening new avenues toward super-resolution and high rate telecommunications.

Time reversal mirrors are not only unique research tools in the field of fundamentals physics but they have plenty of applications including medical imaging, therapy, telecommunications, underwater acoustics, seismology, human-machine interface. An overview of these applications will be presented.

Recently, new tools available in optics such as sensitive and fast megapixel digital sensors and modulators are opening new perspectives toward time-reversal of light.


About the speaker

Prof. Mathias Fink received his PhD in solid state physics from the University of Paris in 1970. Then he moved to ultrasonic medical imaging and received his Doctorat es Sciences degree in Acoustics. He is currently a Professor at the École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI ParisTech), where he founded in 1990 the Wave and Acoustics Laboratory that became in 2009 the Langevin Institute which today brings together, under his supervision as the Director, over 110 scientists engaged in research on waves and imaging.

Prof. Fink’s area of research is concerned with the propagation of waves in complex media and the development of numerous instruments based on this basic research. He pioneered the development of time-reversal mirrors and Time Reversal Signal Processing. He developed many applications of these concepts from medical imaging, ultrasound therapy, telecommunications, seismic imaging, to tactile objects. He also pioneered several innovative medical imaging methods: transient elastography, supersonic shear imaging and multi-wave imaging that are now implemented by several companies. Four companies with close to 270 employees have been created from his research (Echosens, Sensitive Object, Supersonic Imagine and Time Reversal Communications). He holds more than 60 patents, and has published more than 350 peer reviewed papers.

Prof. Fink is a Member of the French Academy of Sciences and of the French Academy of Technologies. He was elected Chair of Technological Innovation at the College de France in 2008.

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