Phase shift and group delay in phononic crystals of pillars on a surface

International audienceThe last years have seen a significant rise in the number of studies of band gap materials for acoustic waves. Basically, these artificial materials can be classified into two distinct families: phononic crystals and acoustic metamaterials. Indeed, they can both prohibit the propagation of acoustic waves in certain frequency ranges for all directions of incidence, but the physical phenomena behind are markedly different. The key parameter to obtain band gaps in the case of phononic crystals is periodicity, while the local frequency resonance of each basic cell dominates in the case of acoustic metamaterial. Propagation of acoustic waves in phononic crystals has been reported for bulk, Lamb and surface acoustic waves. Most of the experimental studies focused on the attenuation involved within band gaps. The purpose of the present paper is to investigate the phase shift and the groupe delay induced by a periodic structure of pillars on a surface in a wide frequency range owning locally-resonant and Bragg band gaps. The experimental dispersion curves are presented accordingly and a very good agreement between theory and experiment is obtained