Reverse Time Migration based Ultrasonic Wave Detection for Concrete Structure

摘要

Ultrasonic wave testing is a classic NDT method to detect, locate and monitor the crack/fracture in construction materials. In this paper, a new ultrasound data interpretation technique is introduced: The reverse time migration (RTM) is a wave equation based pre-stack method used in seismic exploration. Since RTM can utilize all kinds of waves, such as reflection waves, refraction waves and diffraction waves, it has no dip limits in migration and can image the inside of complicated structures. However, the large data generation and sophisticated velocity field analysis are the bottlenecks for RTM that hinder its wide applications. A hybrid boundary condition (including random boundary and absorption boundary simultaneously) is suggested in this paper to reconstruct the source wave field to address the memory storage issues. A numerical model with S-shaped internal fracture is presented to demonstrate the technique for detection of internal flaws. The results indicate that the accuracy of detecting the embedded flaw within construction material is affected by the sampling space and the range of wave frequency.