The excitation and dispersion properties of guided waves in multi-layered plates

The dispersion and excitation mechanisms of the guided waves in multi-layered plates are studied. Firstly, the dispersion equation is obtained by the propagator matrix method. Then, the bisection technique is employed to find all the roots of the dispersion function. The dispersion characteristics of the guided waves are investigated and analyzed. It is found that the velocity limits in high frequency of the first and high modes are equal to the Rayleigh wave and S wave velocities of the low-velocity layer respectively for the multilayered plates in which the S wave velocity increases or decreases from the top to bottom. It is also found that the velocity limit in high frequency of all modes is equal to the S wave velocity of the low-velocity layer for the plate with a low-velocity middle layer. On the aspect of excitation mechanism, the normal displacement spectrum of all the modes excited by the normal force source with a definite width on the surface of the plate is studied. It shows that the dominant mode is the first mode when the S wave velocity increases from the top to bottom, and the dominant mode is different in different frequency range for the plate with decreasing S wave velocity or a low-velocity middle layer.