SAFT Imaging in Concrete Using Movable Ultrasonic Array Elements

We have investigated ultrasonic array imaging in concrete using longitudinal waves. Due to the large volumes and masses of the piezoelectric elements, including the damping material, in the low-frequency range, the assembled array transducer lacks good portability. Although the full matrix capture (FMC) utilizes a combination of transmission and reception signals, not all elements need to be assembled as a single array transducer. We have developed a prototype jig that enables the elements to move smoothly over the concrete surface, allowing the apparent array aperture and lift-off distance to be varied arbitrarily. In this study, moving the two elements for transmission and reception with the jig produces signal combinations necessary for the FMC. Here, we present internal imaging using the synthetic aperture focusing technique with signal combinations obtained from the jig. Our method enables the reconstruction of artificial flaws at depths exceeding 500 mm in concrete.