1State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190 2University of Chinese Academy of Sciences, Beijing 100049
Abstract:The dynamic photoelastic technique is employed to visualize and quantify the propagation properties of backward Lamb waves in a plate. Higher energy leakage of second-order symmetric backward wave mode S$_{\rm 2b}$ in contrast to third-order anti-symmetric backward mode A$_{\rm 3b}$ is shown by the dispersion curve of a plate immersed in water, and then verified by experiments. To avoid the considerable high leakage, the plate is placed in air, both group and phase velocities of modes S$_{\rm 2b}$ and A$_{\rm 3b}$ in the glass plate are experimentally measured. In comparison with the theoretical values, less than 5% errors are found in experiments.