A new method for real-time nondestructive measurement of the distribution of defects in pipe-like objects is proposed.
In this system two ultrasonic waves, a probing wave with continuous low pressure amplitude at relatively high frequency and a pumping wave with impulsive high pressure, are used. They are propagated in opposite directions. Then the information on the change of the pumping wave form due to the defects on the inner wall of a pipe is transferred into a phase change of the probing wave; hence the distribution of defects along the probing wave can be detected by demodulating the phase change of the wave.
The principle, physical construction, a number of signal processing steps to increase the sensitivities, and observed results are presented.