Compact Waveguide and Guided Beam Pattern Based on the Whispering-Gallery Mode of a Hollow Pillar in a Phononic Crystal Plate

We report on the experimental evidence of the guiding of the lowest-order antisymmetric Lamb mode (A0) through a compact waveguide consisting of aligned hollow pillars in between a square-latticed array of solid pillars on a thin slab. We analyze both numerically and experimentally the guiding achievements and we highlight the role played by the whispering gallery mode of the hollow pillars. In particular, we highlight the evolution of the displacement field pattern behind the waveguide that we relate to the emission of a quadrupolar wave interacting with the surrounding solid pillars. We also show the asymmetric transmission of a compact waveguide based on the same mechanism.