Calibration of ultrasonic hardware for enhanced Total Focusing Method imaging

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 ultrasonic data. In this paper, a quick, easy-to-use and robust methodology is proposed to reduce this uncertainty from images generated using the Total Focusing Method (TFM). Using a 128 element linear phased array, multiple Full Matrix Capture data sets 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 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 sample with three side-drilled holes. The time delay errors from transmission and reception are introduced into the time-of-flight calculation for each ray path in the TFM. This results in an enhancement in the accuracy of the defect localisation in the TFM image.