Time-Domain Second-Harmonic Generation of Primary Lamb-Wave Propagation in an Elastic Plate

We present an experimental observation of the generation of the time-domain second harmonic by propagation of the primary Lamb-wave tone-burst. For a case where the phase velocity matching between the primary and the double frequency Lamb waves is satisfied but the group velocity matching between them is not, our observation clearly shows that the duration of the time-domain second-harmonic tone-burst, as well as its integrated amplitude, increases with the increasing propagation distance. This experimental result is consistent with the theoretical prediction and demonstrates that group velocity matching is not absolutely necessary for the generation of the cumulative time-domain second harmonic by primary Lamb-wave propagation.