WP2 | Laboratory experiments
Data acquisitions to prepare and anticipate experimental results at the geophysics scale.
Leader: Institut Langevin, Paris
Manmade metamaterials based on holes in the ground, or solid columns buried inside it, may be, to some extent, ideal metamaterials. As such their properties should be very close to those obtained through analytical or numerical approaches. Yet forests, collections of buildings in a city, and more generally any existing geophysical object approximated as a metamaterial, will deviate from ideal metamaterials due to two main factors:
- the scatterers or resonators may be randomly positioned and,
- their characteristic size may include a random distribution of resonant frequencies (height of the trees, materials of the buildings, etc.).
Within META-FORET, we wish to study at the scale laboratory the transition from ordered to disordered metamaterials, in the context of elastic waves propagating in solids, and more generally in terms of any wave interacting with resonant unit cells.
It is well known that the properties of the bandgap created by locally resonant metamaterials is insensitive to positional disorder, that is, to a random distribution of position of the unit cells. Yet this is true solely if the metamaterial is governed by interferences only. If there exist strong interactions between the unit cells of a metamaterial, it is possible to completely loose the properties of the latter when a large positional disorder is included. For example, we have shown that the bandgap created by elastic rods resonators coupled to asymmetric Lamb waves in a plate give raise to wide band gaps whether the sample are ordered or disordered (Rupin et al, 2014). This means that the physics underlying the metamaterial properties within META-FORET is based on interference effects only to first order.
In WP2, we propose then to study at the lab scale the order-disorder transition in acoustic metamaterials with simple unit cells: soda cans. Part of this work will be studied within the PhD of Simon Yves, who started to work at Institut Langevin this year, while he will later on benefit from the support from the postdoc planned within the META-FORET project.