Personal mobilities made of carbon fiber reinforced plastic (CFRP) laminates are likely to suffer from barely visible impact damages (BVIDs) while the owner is not aware. The BVIDs may cause a significant degradation in the performance, and seriously affect the safety of daily use. Hence, structural health monitoring (SHM) systems that can detect the BVIDs in mobilities are urgently needed. Guided waves (e.g., Lamb waves in plates) are elastic perturbations that can propagate for long distances in thin-wall structures with small attenuation. Hence, they are suitable for SHM system monitoring a large area from a single point. In the previous research, burst waves were used as the input signals to excite Lamb waves, in order to detect an artificial delamination in a CFRP plate by measuring the Time of Flight (ToF) of Lamb waves. However, burst signals with the limited frequency bandwidth are not effective to evaluate the actual impact damage in CFRPs. This is because the actual impact damages are much more complicated than the artificial delamination, and the interaction between ultrasonic waves and the actual damages may vary depending on the frequency. Hence, it is more efficient to detect and evaluate the actual impact damage comprehensively using one broadband signal.
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