Efficient focalization of antisymmetric Lamb waves in gradient-index phononic crystal plates

The focalization of elastic waves within a two dimensional gradient-index phononic crystal (GRIN PC) is numerically and experimentally investigated. The structure is formed by a square lattice of air holes in a silicon plate with transverse variation of holes' diameters. The geometry and efficiency of focalization are computed with a finite element method. A non-contact laser-ultrasonic technique is used both to excite flexural Lamb waves and to monitor in situ the displacements field within the GRIN PC. The efficient subwavelength focusing is achieved and analyzed; furthermore, we describe the oscillatory behavior of focusing and show the relationship between the responses of waves in GRIN PC and the source intensity. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773369]