Improved synthetic aperture focusing technique by Hilbert-Huang transform for imaging defects inside a concrete structure

Abstract

A useful nondestructive testing tool for civil engineering should immediately reveal defects inside concrete structures at the construction sites. To date, there are few effective methods to image defects inside concrete structures. In this paper, a new nondestructive testing method using elastic waves for imaging possible defects inside concrete is developed. This method integrates the point-source/point receiver scheme with the synthetic aperture focusing technique (SAFT) to increase functioning depth and enhance received signals. To improve image quality, received signals are processed by Hilbert-Huang transform (HHT) to get time-frequency curves for the SAFT process. Compared with conventional SAFT method processing with time-amplitude signals, this new method is capable of providing a better image of defects not only in the numerical simulation but also in the experimental result. The image can reveal the number of defects and their locations and front-end profiles. The results shown in this paper indicate that this new elastic-wave-based method exhibits high capability in imaging the defects of in situ concrete structures.

Research on SAFT Imaging Method of Array Probes in Concrete Structures

“…Here F(d m ,t m ) denotes the echo from P in the mth aperture, S(x i ,y j ) is also called the reconstructed pixel [11,12].…”

Extended synthetic aperture focusing technique for ultrasonic imaging of concrete

“…This is often applied along a single analysis axis with each measurement from unique emitting/ receiving pair locations or along a plane with multiple measurements in set shift factors from a single emitting/receiving location [31][32][33]. Using the setup in this study, the general SAFT is formalized to allow for interpretation of signals with sending and receiving transducers located at different locations and to allow for a signal sent from one location to be received at various locations along the surface [34][35].…”

Ultrasonic Pulse Echo Signals for Detection and Advanced Assessment of Reinforced Concrete Anomalies

“…The pulse-echo technique uses the synthetic aperture focusing technique (SAFT), a signal post-processing method that improves the accuracy of an area scan to detect concrete defects. This technique has proved to be highly reliable and has been employed in many studies to locate voids in concrete [2][3][4].…”