Numerical Investigation of the Slow Acoustic Wave Modes in a One-Dimensional Phononic Crystal Plate

The propagation of Lamb waves in a two-layered free standing plate composed of a one-dimensional photonic crystal thin layer coated on uniform substrates of different thicknesses is investigated numerically by the finite element method. We concentrate on the theoretical demonstration of the existence of very slow group velocity at the nearly flat band in specially designed phononic crystal plates and show that the group velocity can be tuned from positive to negative gradually as the thickness of the substrate layer increases. Potential applications in new acoustic devices are described.