Mode extraction technique for guided waves in a pipe

Guided waves propagating in a pipe consist of many modes with different velocities and dispersions. To analyze these complex guided waves through a normal mode expansion technique, that is the fundamental theory on guided waves, we must first extract guided wave modes from received signals. In this study, we develop a mode extraction technique in which many received signals at different circumferential positions can be processed based on the fact that guided wave modes have different displacement distributions in the circumferential direction. After discussing the relevant theory, we verify our mode extraction technique experimentally using eight signals at eight different circumferential positions. Moreover, we show that the circumferential position of an excitation transducer, as well as the distance between an excitation transducer and a receiver in a pitch-catch configuration can be identified using the mode extraction technique.