Determination of Condition for Fastest Negative Group Velocities of Lamb‐Type Waves under each Density Ratio of Solid and Liquid Layers

Abstract

Lamb‐type waves are coupling modes of leaky Lamb waves on a layer structure. The Lamb‐type waves have complicated propagation characteristics more than ordinary Lamb waves on a uniform elastic plate. In the characteristics, we examine the negative group velocities. Generally, the negative group velocities of Lamb waves are slower than positive group velocities under the same condition. If the negative group velocities are applied to fabricating some new application, it is desired that the speeds of negative group velocities are comparable to those of positive group velocities. Consequently, we aim to obtain the faster negative group velocities. Lamb‐type waves show more discriminative characteristics in negative group velocities than ordinary Lamb waves. In this research, we consider the Lamb‐type waves in a solid/liquid/solid structure. It is described the conditions for obtaining the fastest negative group velocities of Lamb‐type waves. The conditions, which are the acoustical impedance ratio, are expressed as the function of the density ratio of solid and liquid layers. These results are verified by numerical calculations.