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Asymptotic and Numerical Analysis of MOdels of Resonant Physics Involving Structured Materials

Final Report Summary - ANAMORPHISM (Asymptotic and Numerical Analysis of MOdels of Resonant Physics Involving Structured Materials)

One way to expand the range of material properties is to adjust the composition of materials at the molecular level using chemistry. An alternative approach is to design structured media (fluids or solids) in which the effective electromagnetic, hydrodynamic or elastodynamic responses result from a macroscopic patterning or arrangement of two or more distinct materials. This project explores the latter avenue to enhance control of ocean waves within artificially structured fluids and seismic waves propagating in structured soils.

Pendry's perfect lens, the paradigm of electromagnetic metamaterials, is a slab of negative refractive index material that takes rays of light and causes them to converge with unprecedented resolution. This flat lens is a combination of periodically arranged resonant electric and magnetic elements. Similar ideas have been implemented in two large scale experiments on structured soils in collaboration between Institut Fresnel (CNRS/Aix-Marseille University/Ecole Centrale Marseille) and the Menard Company (Vinci Group) : In the first experiment led near Grenoble at the foot of the French Alps in August 2012, a seismic source of frequency 50 Hertz has been detoured by an array of boreholes (0.3 m in diameter), which can be considered as a step towards a seismic cloak; in the second experiment led a month afterwards near Lyon (which is a city situated half-way between Paris and Marseille), a seismic source of lower frequency (2 to 10 Hertz) has been refocused by an array of larger boreholes (3m in diameter), which can be attributed to some negative refraction of surface Rayleigh waves. In parallel, small scale experiments have been performed for lensing and cloaking of Lamb waves in thin structured plates, which can be somewhat considered as approximate models for Rayleigh waves in structured soils. Large scale auxetic structures (i.e. displaying a negative Poisson ratio) and inertial resonators buried in the soil have also been investigated, and shown to efficiently damp not only Rayeligh waves but also coupled shear and pressure waves.

Research in acoustic metamaterials also encompasses the design of invisibility cloaks for non-linear surface water waves (e.g. tsunamis) propagating in structured fluids. Maritime and civil engineering applications are sought in the protection of harbours and off-shore platforms. A first design of invisibility carpet for non-linear water waves has been tested in a 17 meters long water channel at Ecole Centrale Marseille in from 2012 to 2014, with subsequent filing of a French patent in 2015 (extended to Europe and USA in 2015) against coastline errosion caused by ocean waves. A small scale ocean cloak has been successfully tested in 2016 in a large wavepool near Marseille (BGO La Seine Sur Mer) in sea storm conditions, and a second patent has been filed, again with CNRS-owned innovation company SATT-SE.

Finally, acoustic wormholes (one can think of them as being undetectable acoustic waveguides, rather than space-time machines!) for an enhanced control of pressure waves in fluids are also being designed for underwater camouflaging.