Time Reversal Guided Waves for Inspecting Crack in Pipeline by Non-axisymmetric Excitation
Currently guided wave time-reversal method for pipe inspection requires using multi-channels to excite and receive signal at the same time.After studying the flexural modal cluster exciting properties,a new time-reversal method based on single oblique transducer with partial loading exciting L(M,2) modal cluster is presented.The feasibility of time reversal focusing method with L(M,2) modal cluster is verified using oblique transducer array and self-developed excitation/receiving board.The focusing effect is experimentally studied in pipeline with crack by using different initial excitation signal types,center frequencies and time reversal window width.The results show that in different inspection frequencies with narrow or wide bandwidth initial excitation signal,amplitude of the defect echo and S/N ratio have significant improvement after using time reversal focusing method,thus defect echo signal can be obviously distinguished by time reversal focusing inspection.