A new type transducer for torsional guided wave generation and its application to defect detection in pipes

A new type transducer used to excite and receive torsional modes has been developed. It consists of several shear mode piezoelectric elements which are in identical thickness and are made by commercial lead titanate zirconate composition materials. When the top and bottom segments of these elements vibrate in opposite direction, shearing deformation in the circumference direction of a pipe is obtained and thus torsional modes are generated. By an experiment, signals in the frequency ranged from 40 kHz to 230 kHz are excited in a 4 m-long steel pipe with the developed transducer. Comparing with theoretical results, it is shown that the transducer can excite and receive the lowest torsional mode T(0,1) mode, in pipes. Furthermore, two completely different kinds of artificial defects are detected with T(0,1) mode which is excited by the transducer.