Enhancements to the Synthetic Aperture Focusing Technique for Through-Transmission Ultrasonic Testing Applied to Concrete Elements

The Synthetic Aperture Focusing Technique (SAFT) is a widely used method for image reconstruction in engineering applications, originally developed for ultrasonic pulse-echo testing. This study introduces an Enhanced Synthetic Aperture Focusing Technique (E-SAFT) specifically adapted for through-transmission ultrasonic testing in concrete elements. E-SAFT key innovations include: (1) suppression of mirror artifacts through the separation and subtraction of dual-image sets arising from symmetric wave paths, (2) retention and use of first-arrival signals to exploit diffraction effects and improve inclusion detection, and (3) application of bidirectional Hilbert transforms to enhance envelope uniformity in multi-directional measurements. The methodology is evaluated in three phases: numerical simulation, experimental testing, and performance quantification using different metrics. Results demonstrate that E-SAFT significantly improves image clarity and inclusion detectability, outperforming conventional SAFT. These findings underscore E-SAFT's potential to advance through-transmission ultrasonic testing in non-destructive evaluation (NDE) of concrete structures.