Institut Langevin - Ondes et Images : Home

Microbubbles flowing over a gelatin surface.

Multiscale elastography: Optical coherence tomography combined with an ultrfast ultrasound scanner. ©CNRS C. Fresillon

Ultrasound spatiotemporal field at the focus of a transducer.

Water tanks for research on acoustics in complex media. ©INSERM P. Latron

Detection of photoacoustic sigal emitted by gold nanoparticles. ©CNRS C. Fresillon

Human brain imaging with optical coherence tomography.

Localization of sources in a cavity. ©CNRS C. Fresillon

Numerical simulations of elastic vibtation modes in a silicium plate.

Optical coherence tomography setup for endoscopy. <a href='https://www.institut-langevin.espci.fr/spip.php?article337'>[more]</a> ©CNRS C. Fresillon

Weekly seminars at the Langevin Institute. ©CNRS C. Fresillon

View of the Langevin Institute, 1 rue Jussieu, Paris 75005, France. ©CNRS C. Fresillon

News

| 2021/09/08 15:29 |

Probing ultrasound scattering and absorption in earth materials

Determination of ultrasound scattering and intrinsic attenuations in heterogeneous media is an important issue from material characterization (polycrystals, porous rocks, cements) to geophysical (...)

| 2021/09/02 18:26 |

Waves in random time-dependent media exhibit universal statistics

Wave propagation in a homogeneous medium in which the wave velocity fluctuates randomly in time is an emerging topic. Previous studies, including at Institut Langevin, have shown that the average (...)

| 2021/07/16 08:38 |

Matrix image of a seismic fault

In geophysics, seismic faults or volcanoes are particularly difficult to image because of the multiscale heterogeneities of the rocks that compose them. Inspired by previous works in ultrasound (...)

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Publications

Gravitational lens effect revisited through membrane waves Catheline, S., V. Delattre, G. Laloy-Borgna, F. Faure, and M. Fink American Journal of Physics 90, no. 1, 47-50 (2022) Abstract: By means of experiments and curved manifold simulations, we show that wave propagation past a topological deviation on a two-dimensional flat fabric membrane is analogous to gravitational lensing. Using an ultrafast camera, we track a membrane plane wave as it crosses a local warped depression. Finite difference simulation, based on the scalar wave equation in a Schwarzschild metric, fully describes the experimental wavefront shape. Comparison between the theoretical and experimental deviation of wave geodesics from straight lines shows that (i) the nonlinear behavior of fabrics due to stretching induces second order effects only and (ii) the experimental depression is closely approximated by the Schwarzschild metric of a gravity well. The experiment demonstrates, in a simple way, how wave propagation is influenced by the topology of the transmission medium.
Liquid walls and interfaces in arbitrary directions stabilized by vibrations Apffel, B., S. Hidalgo-Caballero, A. Eddi, and E. Fort Proceedings of the National Academy of Sciences of the United States of America 118, no. 48 (2021) Abstract: Gravity shapes liquids and plays a crucial role in their internal balance. Creating new equilibrium configurations irrespective of the presence of a gravitational field is challenging with applications on Earth as well as in zero-gravity environments. Vibrations are known to alter the shape of liquid interfaces and also to change internal dynamics and stability in depth. Here, we show that vibrations can also create an "artificial gravity" in any direction. We demonstrate that a liquid can maintain an inclined interface when shaken in an arbitrary direction. A necessary condition for the equilibrium to occur is the existence of a velocity gradient determined by dynamical boundary conditions. However, the no-slip boundary condition and incompressibility can perturb the required velocity profile, leading to a destabilization of the equilibrium. We show that liquid layers provide a solution, and liquid walls of several centimeters in height can thus be stabilized. We show that the buoyancy equilibrium is not affected by the forcing.
Propagation of scalar waves in dense disordered media exhibiting short- And long-range correlations Rohfritsch, A., J. M. Conoir, T. Valier-Brasier, R. Pierrat, and R. Marchiano Physical Review E 104, no. 6 (2021) Abstract: Correlated disorder is at the heart of numerous challenging problematics in physics. In this work we focus on the propagation of acoustic coherent waves in two-dimensional dense disordered media exhibiting long- and short-range structural correlations. The media are obtained by inserting elastic cylinders randomly in a stealth hyperuniform medium itself made up of cylinders. The properties of the coherent wave is studied using an original numerical software. In order to understand and discuss the complex physical phenomena occurring in the different media, we also make use of effective media models derived from the quasicrystalline approximation and the theory of Fikioris and Waterman that provides an explicit expression of the effective wave numbers. Our study shows a very good agreement between numerical and homogenization models up to very high concentrations of scatterers. This study shows that media with both short- and long-range correlations are of strong interest to design materials with original properties.
Cloaking, trapping and superlensing of lamb waves with negative refraction Legrand, F., B. Gérardin, F. Bruno, J. Laurent, F. Lemoult, C. Prada, and A. Aubry Scientific Reports 11, no. 1 (2021) Abstract: We report on experimental and numerical implementations of devices based on the negative refraction of elastic guided waves, the so-called Lamb waves. Consisting in plates of varying thickness, these devices rely on the concept of complementary media, where a particular layout of negative index media can cloak an object with its anti-object or trap waves around a negative corner. The diffraction cancellation operated by negative refraction is investigated by means of laser ultrasound experiments. However, unlike original theoretical predictions, these intriguing wave phenomena remain, nevertheless, limited to the propagating component of the wave-field. To go beyond the diffraction limit, negative refraction is combined with the concept of metalens, a device converting the evanescent components of an object into propagating waves. The transport of an evanescent wave-field is then possible from an object plane to a far-field imaging plane. Twenty years after Pendry’s initial proposal, this work thus paves the way towards an elastic superlens.