We will first focus our research on the addition of spatial disorder to locally resonant sonic crystals, in order to study the formation of localized modes near the band edges of these regularly-ordered media. To do so, low density soda cans samples will be studied in an anechoic chamber using arrays of speakers, microphones, and a 2D translation stage (see Fig. 1). We will perform frequency/space cartography of the acoustic wave field supported by a random medium constituted of Helmholtz resonators with average spacing close to the Bragg frequency of a crystal, that is, half a wavelength.

This experiment will be the small-scale analog of the tree forest experiment in a poplar grove where the density of trees do not exceed 200 trees per hectare with trees height of 40 m that behave as very strong resonators. Indeed 200 trees per hectare correspond roughly to one tree every 7 meters, to be compared with a 15-m wavelength at 30 Hz. An analysis of the locally resonant disordered crystal behavior with respect to the scattering cross-section of the resonators and the amount of disorder added will be performed. Links will be made with the phenomenon of Anderson localization of waves. The results will be compared to analytical approaches based on multiple scattering techniques.

Updated on 5 octobre 2016