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 (A(1)) Lamb wave in a tapered plate respectively carved with sharp bottom corner and round bottom corner is theoretically investigated. Through numerical simulation of A(1) 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 A(1) mode is converted into the fundamental symmetrical S-0 and antisymmetrical A(0) modes to pass through the defected region. Furthermore, the transmitted modes A(0) and S-0 are completely apart from each other and can be quantitatively evaluated. Conversely, when the thickness change is very smooth, most of the energy of A(1) Lamb wave is reflected back. It is the unique mode conversion behavior that leads to great transmission difference value of A(1) 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 theta, height h (1) and h (2). The simple asymmetric systems will be potentially significant in applications of ultrasound diagnosis and therapy.