Abstract: A narrow band high voltage pulse is employed to excite the piezoelectric wafers array that is mounted on the pipe’s exterior surface. And guided wave time reversal method is implemented, which is an efficient way to improve the inspection ability for small defects. All piezoelectric wafers are simultaneously excited by the pulse signal and receive echo signal separately. Then the L(n,2) mode signal segment which includes defects information is selected and reversed in time domain. The time reversal waves are again used as new exciting signals of the corresponding element. Thus the new echoes received by the array almost are purity L(n,2) mode. Experiment results show that this method can limit the dispersion and multi-modes phenomenon. Both signal noise rate and inspection ability of small defects can be improved. No matter before and after time reversal method, guided wave mode of reflected signal from pipe end and defect is almost the same. So group velocity of L(0,2) mode with special frequency can be used as propagating velocity of defect wave package detected by time reversal waves. And the maximum amplitude wave package in defect echo closely matches with the one of narrow bandwidth initial pulse, which can effectively enhance the resolution of the defect echo.

Key words: Piezoelectric wafer array, Pipe, Time reversal inspection, Ultrasonic guided wave