Finite element simulation of laser-generated surface acoustic wave for identification of subsurface defects

Abstract The characteristics of laser-generated ultrasonic wave with subsurface defects are investigated by finite element method (FEM). We used this method to model a subsurface hollow with a rectangular shape, which was used to represent a subsurface defect. The diffracted bulk modes and oscillation modes result from the interaction between R-waves (Rayleigh waves) and subsurface defects are analyzed in detail. The amplitude of RE-waves (Echo waves) and O-waves (oscillating waves) results from subsurface defects change when the depth of subsurface defects increases. The sources and mechanism of E-waves and O-waves were studied. The maximum amplitude of 1-2 MHz, 2-3 MHz and 3-4 MHz changed very obvious and performed oscillation characteristics, we can select the maximum amplitude of laser-generated ultrasonic wave at different frequency can be used to detect the size and location of subsurface defect. The proposed method may provide a useful way to detect other types of subsurface structures.