Visualization of negative refraction of surface acoustic waves by numerical simulations and experiments

We investigate numerically and experimentally the negative refraction of surface acoustic waves in two-dimensional phononic crystals in the MHz range. We performed high-performance time-domain simulations of propagating broadband surface acoustic waves with the Finite Element Method (FEM) and spatio-temporal imaging by means of pulsed optical excitation and interferometric detection. Experimental and numerical evidence is found for negative refraction from surface wave focusing at particular frequencies after wave propagation through a parallel-sided phononic crystal layer. Obliquely incident plane waves on a phononic crystal were also investigated by numerical simulations. The transmitted waves show a clear shift of the wave front at particular frequencies, providing further evidence for negative refraction of the surface acoustic waves.