Piezoelectric transducer excitation for guided waves propagation on pipeline with flexural wave modes

Ultrasonic guided wave inspection is one of the non-destructive testing (NDT) techniques available for the structural health monitoring of engineering structures. Compared with other NDT techniques, guided waves can propagate over tens of metres with a relatively high sensitivity to defects in the structure. For pipeline inspections, by using an array of transducers, guide waves enable the identification of the location of defects on the pipe circumference. The general sensitivity range of the operation is 3% - 9% reduction of the cross-sectional area, depending on the signal-to-noise ratio. However, optimisation of guided wave testing method is still a requirement, as the technique is currently subject to a complex analysis due to wide number of guided wave modes generated. This can be done by optimising the transducer array design. In this paper, the behaviour of a single piezoelectric transducer upon excitation in a tubular structure is assessed. This is achieved through a combination of finite element analysis and experimental studies. A group of wave modes are considered from the torsional T(0,1) mode to several flexural wave modes. The behaviour of a single transducer element is evaluated at a specific frequency of 35 kHz, as it is the interaction of the generated wave modes with simulated notches. The core objective of the work is to use the information gathered to optimise the design of transducer arrays aimed at exciting the T(0,1) mode with a significant level of mode purity. This will significantly reduce the complexity of guided wave analysis, enhancing effectively the health evaluation of structures, and subsequently reduce the industry maintenance cost.