Abstract
Piezoelectric ring-shaped sensor (PeRS) has been widely used for guided wave inspection of piping. The PeRS is normally consisted of plural transducer elements located along circumference at regular interval. Due to the structure, in addition to the axially propagating torsional mode guided waves, circumferential (C-) Lamb waves have also been generated as spurious waves at the same time. Especially in the resonant conditions determined by both the specific frequencies and locations of sensor elements, the C-Lamb waves are dominantly and preferentially generated as actual spurious signals that may distort axially propagating waves. In this paper, this troublesome phenomenon is used not for the axially propagating guided waves but usefully for the measurements of wall thicknesses. The Principle, the verification and the accuracy of the measurements were shown.
