Ultrasonic guided waves have rapidly become an effective device in the field of NDT in recent years. Main reason for this is the ability of transmission from one point on the pipe to travel a long distance along it length. These waves are typically used in relatively low frequencies, and as a result, die out in longer periods of time. In this study, by designing and building a system to generate the needed signal for the stimulation of guided waves through using a piezoelectric crystal, these waves were generated and transmitted along a pipe. After propagation, waves were relieved by an ultrasonic probe and were saved by a digital oscilloscope. The received waves were then processed and filtered to eliminate noise and compared with each other. In order to compare the results and study the effective parameters of inspecting ability by these waves, the receiving probe was moved along the length of the pipe and through clanging the number of entering sinusoidal pulses along with altering the frequency signal; the data was recorded in the highest amplitude frequency. By adjusting the frequency within 30-40 KHz range, it would be possible to receive signals at any point in the experiment. Although the received signals weaken by further distance, however; through increase in the number of pulses of inlet signals, the guided waves better stimulate and become stronger at the outlet signal.
One of the most important parameters in the area of structural inspections is nondestructive testing. In recent years, a
new approach known as "ultrasound guided waves" has been developed in the field of ultrasonic testing. The main
advantages of this method are ability of propagation along the structure and inspection of long distances, high speed and
low cost. In this study, a sinusoidal input signal with three pulses has been used for excitation of guided waves. These
waves have been propagated along the pipe and data capturing has been performed in three positions. Afterwards, a saw
cut has been applied on the pipe as a crack and the receiving signals have been recorded in the same positions. Upon
capturing, signals have been processed and compared via wavelet analysis. Variations in wave amplitudes due to passing
the crack has been investigated and signals have been compared simultaneously in both time and frequency domain by
means of wavelet analysis. Results indicate that even if the crack is not detected, presence of crack in the way of passing
wave will affect the amplitude of propagating wave, yet it does not have any effect on the frequency and time contents of
the signal.
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