A Pulse/Echo Technique with Compensating Dispersion Effect of Ultrasonic Guided Waves

摘要

A pulse/echo technique using the compensating dispersion effect of ultrasonic guided waves is proposed. The technique is based on excitation of a time-inversed dispersed guided wave that can focus on a particular axial position on a pipe. In the technique, the propagating guided wave has a maximum amplitude at the focal position by being in phase for all frequency components. The technique can be used for the pulse/echo mode in long range testing with the following procedures: determining multiple focal positions along the pipe; transmitting time-inversed dispersed signals suitable for each focal distance; extracting a gated signal corresponding to the focal position; and combining the gated signals into a merged signal. The proposed technique was tested experimentally and its principle was confirmed to be valid for both the pulse/echo and through-transmission modes. It was also confirmed that the technique had the effect of enhancing the wanted mode and relatively suppressing the spurious modes. Small artificial discontinuities that could not be detected by the conventional sine burst transmission technique could be detected by the proposed technique.