Flat lens for pulse focusing of elastic waves in thin plates

The ability of left-handed materials to overcome the diffraction limit was first considered as one of the most exciting and challenging outcomes of the negative refraction concept. Flat lens focusing of elastic waves is, however, a challenge. We demonstrate broadband focusing of elastic waves at 10 kHz carrier frequency, below the first stop band, in a 45°-tilted square array of circular air holes perforated in a Duraluminium thin plate. By adjusting the relative thickness of the outer plate we achieve large-angle negative refraction with diffraction-limited lateral resolution. We find good agreement with a simple beam-lattice model and finite-difference time-domain simulations.