Lamb Wave Arrival Time Extraction Using Hilbert-Huang Transform for Improved Tomography Image

Travel time Lamb wave tomography has been shown to be an effective nondestructive evaluation (NDE) technique for plate-like structures.The methods used previously to extract arrival times of the fastest or multi Lamb wave modes are mostly based on various time-frequency methods such as Wigner-Ville distribution,short-time Fourier transform,and recently explored wavelet transform(WT).Frankly speaking,uses of these signal processing methods improve the accuracy of the arrival time extraction to a great extent relative to directly extract arrival times in time-domain from Lamb waveforms.Hilbert-Huang transform(HHT) is also an efficient way for analyzing and processing non-stationary signals.The resolving power of time and frequency is restricted from Heisenberg principle in wavelet analysis,while in HHT,the time resolving power is precise and steady,and frequency resolving power is adaptive according to signal intrinsic characteristics.Conclusion can be made that the HHT method is more adaptive than WT analysis in analyzing non-stationary signals.Based on the above,HHT method is attempted to extract arrival times from Lamb waveforms in this paper.The Lamb wave tomography images generated with arrival times from HHT method were compared with those of WT.The results show that the new method improves the quality of tomography image,which demonstrates the applicability of HHT method in extracting arrival times of Lamb waves.