Synchrosqueezing Transform Matched to Nonlinear Group Delay for Mode Estimation of Ultrasonic Guided Waves.

Ultrasonic guided waves (UGW) are often used in structural health monitoring applications to identify possible damage sensitive features in complex materials. It is thus important to characterize the properties of the multiple frequency-dependent modes of UGW propagation in dispersive material. We propose a novel synchrosqueezing transform that is designed to provide high localization to signals with nonlinear time-frequency group delay signatures. The transform is well-matched to the strong modulation of UGW propagation. It can also provide mode separation and reconstruction of highly dispersive signal components. The performance of the transform is demonstrated and compared to other recently developed synchrosqueezing transforms using both simulated and real data.