Second-harmonic generation of Lamb waves in a solid layer on a half space

This is work develops an effective approach for studying second-harmonic generation of Lamb waves in the composite structure consisting of a solid layer on a half space. Using a second-order perturbation approximation and a modal expansion analysis approach for waveguide excitation, an effective theoretical model has been established. The fields of second harmonics of Lamb waves can be regarded as superpositions of a finite series of normal double frequency Lamb waves (DFLW). Despite the strongly dispersive nature of Lamb waves, it is found that a DFLW can grow with propagation distance down the composite structure when the DFLW phase velocity equals that of the primary Lamb wave.