[3A5] A thickness correction algorithm for permanently installed inductively coupled ultrasonic transducer systems

Y Chen, A Croxford, P Wilcox and J Zhang
University of Bristol, UK 

An inductively coupled ultrasonic transducer system (ICTS) in non-destructive evaluation (NDE) is a low-profile, wireless, and battery-free permanently installed sensor system for measuring remaining wall thickness at fixed locations for structural health monitoring (SHM). In an ICTS, a slight variation in measured thickness has been observed that is dependent on the misalignment between the handheld probing unit and the permanently attached sensor. A thickness correction algorithm has been developed to improve the ultimate thickness measurement performance of ICTS even with misalignment. The algorithm eliminates a system delay from the measured first arrival time based on the measured bandwidth of the crosstalk signal. Crucially, the algorithm does not require identification of the second back wall echo as this is not always possible if the back wall is badly corroded. The thickness correction algorithm has successfully reduced the thickness variability from 0.2mm to 0.07mm and enabled the detection of a thickness loss of 0.09mm. Overall, both the accuracy and precision of thickness measurement using ICTS are improved using the proposed algorithm. This is important for future robotic deployment which will become more viable as up to 20mm misalignment can be accommodated.