Team organization may help swarms of flies to become invisible in closed waveguides

Lucas Chesnel (1, 2) , Sergei Nazarov (3, 4)

1 DeFI - Shape reconstruction and identification
2 CMAP - Centre de Mathématiques Appliquées - Ecole Polytechnique
3 SPbU - St Petersburg State University
4 SPSPU - Saint Petersburg State Polytechnical University

We are interested in a time harmonic acoustic problem in a waveguide containing flies. The flies are modelled by small sound soft obstacles. We explain how they should arrange to become invisible to an observer sending waves from −∞ and measuring the resulting scattered field at the same position. We assume that the flies can control their position and/or their size. Both monomodal and multimodal regimes are considered. On the other hand, we show that any sound soft obstacle (non necessarily small) embedded in the waveguide always produces some non exponentially decaying scattered field at +∞ for wavenumbers smaller than a constant that we explicit. As a consequence, for such wavenumbers, the flies cannot be made completely invisible to an observer equipped with a measurement device located at +∞.

Mots clés: invisibility; acoustic waveguide; asymptotic analysis; small obstacles; scattering matrix

Domaines: Equations aux dérivées partielles [math.AP]

Lucas Chesnel, Sergei Nazarov. Team organization may help swarms of flies to become invisible in closed waveguides. 2016. ⟨hal-01216135v2⟩