Estimation of time-of-flight based on threshold and peak analysis method for microwaves signals reflected from the crack

This paper will propose a new approach for Time-of-flight (TOF) estimation based on the peak analysis and threshold method, signal processing procedure developed to precisely evaluate crack position in pipes. In order to acquire a crack position, TOF of the waves reflected from the crack can be estimated from the time domain signal. In this regard, to obtain a crack position with sufficient accuracy, there is a necessity to enhance precision of the measured TOF. First, the original signal is denoised by the wavelet transform smoothed with Savitzky–Golay filtering. Next, to extract appropriate peak, Hilbert Transform is used to construct the signal envelope. After applying peak extraction technique to the signal envelope, the time of the extracted peak has been considered as a TOF. Finally, crack position has been evaluated by calculating group velocities of the propagated waves in each waveguide of the detection system and test pipe.