Superlensing effect for surface acoustic waves in a pillar-based phononic crystal with negative refractive index

We demonstrate super resolution imaging for surface acoustic waves using a phononic structure displaying negative refractive index. This phononic structure is made of a monolithic square lattice of cylindrical pillars standing on a semi-infinite medium. The pillars act as acoustic resonator and induce a surface propagating wave with unusual dispersion. We found, under specific geometrical parameters, one propagating mode that exhibits negative refraction effect with negative effective index close to -1. Furthermore, a flat lens with finite number of pillars is designed to allow the focusing of an acoustic point source into an image with a resolution of λ 3, overcoming the Rayleigh diffraction limit.