Ultrasonic inspection of industrial components with complex geometries using optimised single transmission modulated signals and a flexible ecofriendly ultrasonic array

This work employed a commercial lead-free 20 MHz 64-element 1 mm-pitch 5 mm-elevation linear array combined with coded excitations to inspect thick complex components while achieving higher resolution relative to conventional non-destructive testing frequencies. The imaging performance of the array was assessed via full matrix capture and the total focusing method (TFM). A comparative study (simulation and experimentation) including pulse, Barker and chirp excitations evaluated TFM images employing a novel signal-to-noise ratio (SNR) methodology. The technique considered three frequencies to efficiently select the computation region for SNR characterisation on images. The first study inspected a planar steel component with a target reflector. A representative simulation anticipated sidelobe and matched filter artefacts, along with improved SNR for coded excitation over pulse excitation. This was verified experimentally, with an SNR gain exceeding 1.9 dB. Averaging the single-cycle pulse increases SNR at the expense of slower acquisition, whereas coded excitations improve SNR while maintaining acquisition speed. Moreover, the study was extended to deploying the array and coded excitation methodologies on convex and concave samples. The resulting TFM images detected side-drilled holes showing imaging artefacts. The coded excitation achieved a higher SNR compared to the pulse excitation. These experiments showcased the conformity of the array to the samples.