Mesoscopic wave physics in fish shoals

Benoit Tallon,Sergey E Skipetrov,Guillaume Matte,Jean Guillard,Philippe Roux

doi:10.1063/5.0005145

Abstract

Ultrasound scattered by a dense shoal of fish undergoes mesoscopic interference, as is typical of low-temperature electrical transport in metals or light scattering in colloidal suspensions. Through large-scale measurements in open sea, we show a set of striking deviations from classical wave diffusion, making fish shoals good candidates to study mesoscopic wave phenomena. The very good agreement with theories enlightens the role of fish structure in such a strong scattering regime that features slow energy transport and brings acoustic waves close to the Anderson localization transition.

Highlights

Since the late 1980s, physicists have achieved great progress in the fabrication of strongly disordered materials that would allow for the Anderson localization of “classical” waves (e.g., light, microwaves, and sound) in three dimensions.1–3 Anderson localization is a halt of propagation due to disorder.4,5 very few experiments have succeeded,6–8 these studies have revealed the “mesoscopic” interference phenomena9,10 that are analogous to that of low-temperature electrical transport10,11 (for instance, weak localization,12,13 strong fluctuations, and long-range correlations of scattered intensity14,15)
Since the late 1980s, physicists have achieved great progress in the fabrication of strongly disordered materials that would allow for the Anderson localization of “classical” waves in three dimensions.1–3 Anderson localization is a halt of propagation due to disorder.4,5 very few experiments have succeeded,6–8 these studies have revealed the “mesoscopic” interference phenomena9,10 that are analogous to that of low-temperature electrical transport10,11
We show that shoals of fish trapped in large cages—an example of live, active matter—allow the examination of various mesoscopic interference phenomena in ultrasound scattering for fish densities that are comparable to those encountered in natural fish schools at sea

Summary

Introduction

Since the late 1980s, physicists have achieved great progress in the fabrication of strongly disordered materials that would allow for the Anderson localization of “classical” waves (e.g., light, microwaves, and sound) in three dimensions.1–3 Anderson localization is a halt of propagation due to disorder.4,5 very few experiments have succeeded,6–8 these studies have revealed the “mesoscopic” interference phenomena9,10 that are analogous to that of low-temperature electrical transport10,11 (for instance, weak localization,12,13 strong fluctuations, and long-range correlations of scattered intensity14,15). The scattering strength of fish shoals is demonstrated via the measurements of long-range correlations or the non-Rayleigh distribution of the intensity speckle, as well as via the dynamic coherent backscattering (CBS) effect, revealing the lowest energy velocity observed in underwater acoustics.

Results

Conclusion