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The accurate estimation of ultrasonic Time-OfFlight (TOF) is essential in ultrasonic non-destructive testing (NDT). In this paper, a new method for TOF estimation through envelope is proposed. Firstly, the Hilbert transform (HT) is used in ultrasonic signal processing in order to extract the envelope of the echo and to reduce the computational burden. Then, the wavelet denoising technique is applied to the extracted noisy envelope to improve the estimation accuracy. Finally, the Space Alternating Generalized Expectation-Maximization (SAGE) algorithm is adopted to estimate the parameters of M-superimposed echoes. Numerical simulation and experimental results have been carried out to show the performances of the proposed method in estimating TOF of ultrasonic signal.

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