Lamb wave mode decomposition for structural health monitoring

• A Lamb wave mode decomposition method is proposed based on two rules.
• The first rule is the group velocity ratio rule.
• The second rule is the mode amplitude ratio rule.
• The proposed method is validated through the experiment.

Lamb waves propagate over large distances in plate-like thin structures and they have received great attention in the structural health monitoring (SHM) field as an efficient means to inspect a large area of a structure by using only a small number of sensors. The times-of-flight of the Lamb wave modes are useful for detecting damage generated in a structure. However, due to the dispersive and multi-mode nature of Lamb waves, it is very challenging to decompose Lamb wave modes into symmetric and anti-symmetric modes for potential applications to structural health monitoring. Thus, we propose an efficient Lamb wave mode decomposition method based on two fundamental rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of A0A0 and S0S0 modes must be constant. The mode amplitude ratio rule means that the ratio of the magnitudes of A0A0 and S0S0 modes in a measured response signal must be always greater than one once the center frequency of the input signal is determined, such that the magnitude of the A0A0 mode in the excited signal is larger than that of the S0S0 mode, and vice versa. The proposed method is verified through experiments conducted for a plate specimen.