Contact : Pr. Régis Wunenburger (regis.wunenburger @ upmc.fr)

Description : Acoustic metamaterials are composite materials which are designed so that the propagation of acoustic waves exhibits remarkable properties in specific frequency ranges like band gaps or negative effective refractive index. These unique properties allow to foresee original strategies of control of the propagation of acoustic waves with potential applications to guiding, filtering, imaging, non destructive control, isolation, cloaking… In the frame of the ANR funded Metakoustik project (2012---2015), which gathers 4 research teams from CRPP (Bordeaux), I2M (Bordeaux), LoF (Bordeaux), and d’Alembert Institute (Paris), we work on the design, the synthesis by physico--- chemistry and microfluidics, and the acoustic characterization of so---called locally resonant acoustic metamaterials, i.e. whose microstructure is made of mechanical resonators: drops, bubbles, hard core---soft shells particles, with the aim of obtaining these non usual propagation properties in the ultrasonic frequency range.

Two realistic designs of metamaterials supposed to work in the ultrasonic frequency range could be indentified: a dispersion of dense spheres in a hard matrix, and more promisingly, a dispersion of dense spheres coated with a thin polymer shell [1]. These materials are presently being produced in LoF. In close collaboration with the postdoc in charge with their synthesis, the postdoc working in Institut d’Alembert will be in charge of :

• implementing a new acoustic characterization bench in order to extract more precisely the properties of the materials composing the metamaterials (celerity and absorption of longitudinal waves, density), then of the metamaterials themselves,
• measuring the complex shear modulus of the materials composing the metamaterials by using a transverse wave bench, with the aim of evidencing the expected unique propagation properties of the synthesized dispersions (band gap) and possibly of their combination with encapsulated bubbles (negative effective refractive index).

[1] L. Bos, L. Lukyanova, R. Wunenburger, Constraints on the design of core---shell resonators of  locally resonant acoustic metamaterials, Phys. Rev. B 86, 184107 (2012).

[2] R. Tadmouri, et al., Millifluidic production of metallic microparticles, Soft Matter 8, 10704 (2012).

Salary: net 24 400€ / year (gross 30 000€ / year) (CNRS---Solvay postdoctoral grant)