Reverse time migration: introducing a new imaging technique for ultrasonic measurements in civil engineering

Abstract

Ultrasonic echo testing is widely used in non-destructive testing in civil engineering to investigate concrete structures, to measure thickness, and to locate and characterise built-in components or inhomogeneities. Currently, synthetic aperture focusing techniques are mostly used for imaging. These algorithms are highly developed but have some limitations. For example, it is not possible to image the lower boundary of built-in components like tendon ducts or vertical reflectors. We adopted reverse time migration for non-destructive testing in civil engineering in order to improve the imaging of complicated structures in concrete. By using the entire wavefield, including waves reflected more than once, there are fewer limitations compared to synthetic aperture focusing technique algorithms. As a drawback, the required computation is significantly higher than that for the techniques currently used.Simulations for polyamide and concrete structures showed the potential for non-destructive testing. The simulations were followed by experiments at a polyamide specimen. Here, having acquired almost noise-free measurement data to test the algorithm, we were able to determine the shape and size of boreholes with sufficient accuracy. After these successful tests, we performed experiments at a reinforced concrete foundation slab. We obtained information from the data by reverse time migration, which was not accessible by traditional imaging. The imaging of the location and structure of the lower boundary of the concrete foundation slab was improved. Furthermore, vertical reflectors inside the slab were imaged clearly, and more flaws were found. It has been shown that reverse time migration is a step forward in ultrasonic testing in civil engineering.

Development of an Accurate and Robust Air-Coupled Ultrasonic Time-of-Flight Measurement Technique

“…The specimen was a polyamide 6 block with dimensions mm, and the signal was transmitted through the mm wide dimension. Due to its homogeneity, polyamide is often used as a reference material for bulk wave ultrasonic testing [ 50 , 51 , 52 ]. A PCB 352M66 accelerometer (PCB Piezotronics, USA) was mounted to the specimen using 1 mm double-sided adhesive tape as the back wall sensor.…”

Zerstörungsfreie Ultraschallprüfung dicker und hochbewehrter Betonbauteile

“…B. in Transmissionsanordnung, ausgewertet werden können. Dabei soll unter anderem die derzeit in Erprobung befindliche RTM‐Methode zum Einsatz kommen .…”

A non-reflecting wave equation through directional wave-field suppression and its finite difference implementation

“…Recently, RTM, which has been developed for geophysical imaging, has also found its way to ultrasound applications like civil engineering 8 , 9 and photo-acoustic imaging 10 . In medical applications, RTM has also shown to be successful in imaging breast-tissue using frequency domain finite difference modeling (FDFD) 11 , 12 .…”