Effects of array transducer inconsistencies on total focusing method imaging performance

The total focusing method (TFM) is a post-processing imaging algorithm for ultrasonic array data in which the array is synthetically focused at every image pixel. In this paper, the performance of the TFM imaging algorithm is examined in the presence of inter-element variability in the array, coupling and instrumentation. The inter-element variability includes amplitude, phase and delay inconsistencies. First, typical experimentally observed inter-element variations are extracted by back-propagation of the pulse-echo signals reflected from the planar back wall of a defect-free sample. The effect of different degrees of variability in the amplitude, phase and time delay associated with each element is then investigated through simulation. The peak amplitude and a measure of the size of the point spread function are used to assess the quality of TFM images simulated for a 1 mm side-drilled hole. It is shown that the performance is most sensitive to variability of time-delay rather than amplitude or phase. (C) 2011 Elsevier Ltd. All rights reserved.