Negative refraction of longitudinal waves in a two-dimensional solid-solid phononic crystal

Abstract

Negative refraction of longitudinal waves is evidenced experimentally in a two-dimensional phononic crystal (PC) with a solid matrix. The PC is made of a triangular arrangement of steel rods embedded in epoxy. The dispersion curves present a branch with a negative slope, corresponding to a mixed mode with a predominantly longitudinal behavior. Experiments are carried out on a prism-shaped PC inserted inside an epoxy block, and excited with a longitudinal transducer. Measurement of the refraction angle at the output side of the PC shows the negative refraction of longitudinal waves through a solid PC. Theoretical results agree quite well with the experimental results. The possibility to use the PC in a fluid background is verified numerically, with the simulation of a focusing flat lens.