Lamb waves filtering by waveguides with linear varying section

Abstract

This experimental and numerical work deals with the study of Lamb modes propagating in a plate with a linear variation of thickness. The varying section area exhibits a filtering phenomenon for Lamb modes having a frequency-thickness cutoff. If the incident Lamb wave, excited at a given frequency and propagating downslope, reaches its thickness cutoff in the varying section area, it is reflected and propagates upslope. Otherwise, it is transmitted outside the varying section domain with modes conversion. The S2 incident mode is a particular case : when it reaches its cutoff , it is converted into the S1 mode with negative groupe velocity and a downslope propagation; then the S1 Lamb wave is reflected at its cutoff. The experimental and numerical studies are in good agreements.