Calibration of ultrasonic hardware for enhanced total focusing method imaging

• Published in: Insight (Northampton) Vol. 62; no. 7; pp. 408 - 415
• Main Authors: Ingram, M, Gachagan, A, Nordon, A, Mulholland, A J, Hegarty, M
• Format: Journal Article
• Language: English
• Published: The British Institute of Non-Destructive Testing 01.07.2020
• ISSN: 1354-2575; 1754-4904
• DOI: 10.1784/insi.2020.62.7.408

Experimental variation from ultrasonic hardware is one source of uncertainty in measured ultrasonic data. This uncertainty leads to a reduction in the accuracy of images generated from these data. In this paper, a quick, easy-to-use and robust methodology is proposed to reduce this uncertainty in images generated using the total focusing method (TFM). Using a 128-element linear phased array, multiple full matrix capture (FMC) datasets of a planar reflection are used to characterise the experimental variation associated with each element index in the aperture. Following this, a methodology to decouple the time-domain error associated with transmission and reception at each element index is presented. These time-domain errors are then introduced into a simulated array model used to generate the two-way pressure profile from the array. The side-lobe-to-main-lobe energy ratio (SMER) and beam offset are used to quantify the impact of these measured time-domain errors on the pressure profile. This analysis shows that the SMER is raised by more than 6 dB and the beam is offset by more than 1 mm from its programmed focal position. This calibration methodology is then demonstrated using a steel non-destructive testing (NDT) sample with three side-drilled holes (SDHs). The time delay errors from transmission and reception are introduced into the time-of-flight (TOF) calculation for each ray path in the TFM. This results in an enhancement in the accuracy of defect localisation in the TFM image.