Single mode extraction from multiple modes of lamb wave and its application to defect detection

Lamb waves generally consist of many dispersive modes, which makes mode identification difficult. This study describes the extraction of a single mode from multiple modes. The single mode extraction is based on two-dimensional Fast Fourier Transform (2D FFT) in time and space, signal filtering, and 2D inverse FFT. An aircoupled ultrasonic technique was adopted for non-contact fast measurements. Using this technique, the A0 and S0 mode were clearly detected in preliminary tests of intact plates. Furthermore, multiple reflections of the A0 mode, which were shown only in the computer simulation, were experimentally confirmed in reflection tests of plates with a rectangular notch. In the reflection tests, two reflected waves were extracted in the intervals corresponding to notch widths.