Negative refraction of surface acoustic waves in the subgigahertz range

International audienceWe used the picosecond ultrasonic technique to experimentally demonstrate the negative refraction of surface acoustic waves in a two-dimensional phononic crystal. The sample is made of a square lattice of circular voids drilled at the surface of a thick silica substrate. The lattice parameter is of a few micrometers. Broad band surface acoustic waves with Fourier components in the gigahertz range were excited. The negative refraction is observed for Rayleigh waves with frequencies in the second band and propagating along the direction ΓM in the reduced Brillouin zone. We then used a plane-wave expansion method to calculate the dispersion of the waves in our sample and to analyze our experimental data