Asymmetric propagation of the first order antisymmetric lamb wave in a tapered plate based on time domain analysis

The asymmetric propagation of the first order antisymmetric (A1) Lamb wave in a tapered plate respectively carved with sharp bottom corner and round bottom corner is theoretically investigated. Through numerical simulation of A1 Lamb wave in time domain, we find that when the thickness of the waveguide abruptly decreases to below the cut-off thickness, about half of the A1 mode is converted into the fundamental symmetrical S0 and antisymmetrical A0 modes to pass through the defected region. Furthermore, the transmitted modes A0 and S0 are completely apart from each other and can be quantitatively evaluated. Conversely, when the thickness change is very smooth, most of the energy of A1 Lamb wave is reflected back. It is the unique mode conversion behavior that leads to great transmission difference value of A1 Lamb wave along the opposite directions. Finally, the influence of geometrical parameters on the transmission coefficient is also studied. The higher efficiency and proper working frequency range can be realized by adjusting the slope angle θ, height h1 and h2. The simple asymmetric systems will be potentially significant in applications of ultrasound diagnosis and therapy.