The total focusing method (TFM) is a synthetic aperture beam forming technique that has been under active development in the NDT industry over the past decade.
In this paper, we introduce a newly developed semi-analytical model to predict the total focusing method (TFM) amplitude sensitivity map for both nondirectional and directional flaws. For complicated acoustic paths that involve multiple interface interactions and wave-mode conversions, a knowledge of the Acoustic Influence Map (AIM) enables an inspector to refine the scan plan to maximize the signal-to-noise ratio of the resultant TFM image and increase the probability of flaw detection. The accuracy of this new acoustic model was tested and validated by experiments using test blocks that contain side-drilled holes and flat-bottom holes. Results from the validation experiments show good agreement between the empirical TFM amplitude maps and theoretical AIM. The results also indicate that the model can be used to guide the selection of the optimal TFM inspection mode.
The total focusing method (TFM) is a synthetic aperture beam forming technique that has been under active development in the NDT industry over the past decade [1]. By applying appropriate transmission and reception delays to A-scan data collected in a full matrix capture (FMC) dataset, TFM can electronically focus on every location within an inspection region. Since every point is electronically focused, TFM can provide better resolution compared to conventional phased array ultrasound inspection techniques. In addition, by calculating and applying the time of flights of multiple acoustic modes, multi-mode TFM that can provide additional information about the specimen being inspected [2].