Ray-based SAFT for Imaging Concrete Structures from Ultrasonic Data

Synthetic aperture focusing technique (SAFT) is one of the most-used ultrasonic imaging algorithms. However, by considering only the direct sound path (i.e., pulse-echo signals) for image reconstruction, this technique is unable to show steeply inclined interfaces and bottom boundaries of objects in concrete structures. To address this problem, the current study considered various sound paths when applying SAFT for concrete elements. The proposed hypothesis is that different sound paths will provide access and imaging opportunities to previously inaccessible areas of the inspected volume/region. As a proof of concept, the proposed method, namely the ray-based SAFT, was tested with ultrasonic shear wave data for two concrete slab specimens. The results indicated a significant improvement compared to conventional SAFT imaging for simulated rebar debonding, vertical boundaries of slabs, and bottoms/sides of tendon ducts.