Mode identification and extraction of broadband ultrasonic guided waves

Lamb waves have dispersion and multimodal characteristics, which are the major reasons for the complexity of their signals. A signal processing technique is established to extract individual dispersive waveforms from raw received Lamb wave signals, even when they interfere with each other in the time-frequency domain. In this technique, the prior knowledge of the dispersion characteristic is utilized for mode identification. On this basis, the propagation distances of concerned modes are estimated and ridge tracking is completed in the interfered neighboring area. Subsequently, an effective time-varying filter, the Vold-Kalman filter, is introduced to isolate these interfered wave modes. When each mode is extracted from the overall Lamb wave signal, accurate quantitative data on propagation characteristics such as energy, attenuation, amplitude, and reflection coefficients can be accurately estimated. The results illustrate a strategy for optimal design of Lamb wave inspections in either a pulse-echo or pitch-catch configuration.