Negative reflection of elastic waves in complex environments

A negative reflecting mirror converts a wave of positive phase velocity into its negative counterpart and vice versa. Whatever the complexity of the propagation medium, the negatively reflected wave field focuses back towards the initial source location, thereby mimicking a phase conjugation operation while being a fully passive process. In this paper, we experimentally demonstrate this phenomenon with elastic waves in a 2D billiard and in a disordered plate by means of laser interferometry. These proof-of-concept experiments show that negative reflection can be a tool of choice for the control and focusing of waves in complex environments.