Waves, complexity and information (OCI)

Rod forest : a ultrasonic multiple scattering model

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Alexandre AUBRY

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Julien DE ROSNY

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Arnaud DERODE

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Mathias FINK

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Marc GUILLON

Abdelwaheb OURIR

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Sébastien POPOFF

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Tutorial: How to build and control an all-fiber wavefront modulator using mechanical perturbations Shekel, R., K. Sulimany, S. Resisi, Z. Finkelstein, O. Lib, S. M. Popoff, and Y. Bromberg Journal of Physics: Photonics 6, no. 3, 033002 (2024) Abstract: Multimode optical fibers support the dense, low-loss transmission of many spatial modes, making them attractive for technologies such as communications and imaging. However, information propagating through multimode fibers is scrambled, due to modal dispersion and mode mixing. This is usually rectified using wavefront shaping techniques with devices such as spatial light modulators. Recently, we demonstrated an all-fiber system for controlling light propagation inside multimode fibers using mechanical perturbations, called the fiber piano. In this tutorial we explain the design considerations and experimental methods needed to build a fiber piano, and review applications where fiber pianos have been used.
Solution to the cocktail party problem: A time-reversal active metasurface for multipoint focusing Bourdeloux, C., M. Fink, and F. Lemoult Physical Review Applied 21, no. 5, 054039 (2024) Abstract: The cocktail party effect is the capability to focus one's auditory attention on particular audio sources while ignoring other audio sources. We propose an experimental strategy to reproduce this ability by designing a time-dependent metasurface composed of independent active mirrors. Each active mirror is a programmable acoustic unit cell capable of hearing, computing, and re-emitting acoustic signals: each of them acts as a convolution filter. The proper configuration of the metasurface temporal filters allows one to establish an acoustic communication link between groups of individuals immersed in the noisy environment: a multiple-user multiple-input, multiple-output acoustic system is built. Keywords: metasurface;cocktail party;time reversal
Topology optimization for microwave control with reconfigurable intelligent metasurfaces in complex media Karamanos, T. D., M. Fink, and F. Lemoult Physical Review Applied 21, no. 4 (2024) Abstract: Reconfigurable intelligent metasurfaces have been proposed as an efficient solution for improving wireless telecommunication systems in multiple-scattering or reverberating media. Concurrently, topology optimization has been successfully used as an inverse-design technique in many fields, and particularly in electromagnetics. In this work, we apply a gradient-based topology optimization for tuning the binary elements of a metasurface for a focusing goal in a complex environment. First, the metasurface unit cells are approximated as point sources and, then, the optimization problem is formulated. Afterwards, the proposed method is applied to find the optimal parameter sets for three distinct environments of increasing complexity, and the resulting focus for each case is demonstrated via numerical simulations. The combination of a reverberating cavity and a metasurface inside the latter is very powerful since everything can be solved analytically for focusing outside the cavity.
Airborne ultrasound for the contactless mapping of surface thoracic vibrations during human vocalizations: A pilot study Wintzenrieth, F., M. Couade, F. Lehanneur, P. Laveneziana, M. C. Niérat, N. Verger, M. Fink, T. Similowski, and R. K. Ing AIP Advances 14, no. 3 (2024) Abstract: Physical examination of the thorax is key to the clinical diagnosis of respiratory diseases. Among other examination techniques, palpation evaluates the transmission of high-frequency vibrations produced by vocalizations (tactile fremitus), which helps the physicians to identify abnormalities within the respiratory system. We propose the use of an airborne ultrasound surface motion camera (AUSMC) to quantitatively map the vibrations induced by subject vocalization. This approach could make the examination of vocal fremitus quantifiable, reproducible, and archivable. Massive data collection of vocal fremitus could allow using artificial intelligence algorithms to isolate vibration patterns that could help disease identification. Until now, in contrast, the interpretation of vocal fremitus has been subject to the physician’s experience and remains subjective. In the present work, we demonstrate the capabilities of the AUSMC to measure vocal fremitus thoracic vibration maps on 77 healthy volunteers. We have observed a spatial dependence of vibration maps on vocalization frequency. We observed that the left lung generates fewer surface vibrations than the right one, which was expected according to their respective dimensions. We also discuss the implications of our findings.

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The technological and scientific advances of the past fifteen years, to which the Langevin Institute has made pioneering contributions, have significantly expanded our ability to control optical, electromagnetic, and acoustic fields with unprecedented spatiotemporal precision. Thanks to these developments, it is now possible to explore and exploit an impressive number of degrees of freedom, thus opening up innovative prospects for numerous applications.

On one hand, telecommunications particularly benefit from these advances, enabling faster, more reliable, and more secure transmissions. On the other hand, imaging in complex media has greatly benefited from these progresses through a comprehensive matrix approach, fully leveraging all available information to significantly improve the quality and precision of the images obtained.

In parallel with these applied works, more fundamental studies are being conducted, notably on gravity waves, which are particularly suitable for exploring time-dependent media. These fundamental research efforts are essential to deepen our understanding of complex phenomena and to open new research pathways.

Thus, the manipulation of information in complex environments is becoming more sophisticated and efficient, facilitating developments in various sectors such as medicine, earth sciences, engineering, and many others.

In summary, the contributions of the Langevin Institute play a crucial role in transforming these scientific discoveries into practical and innovative solutions, thereby redefining the boundaries of what is possible.

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