Fig. 1. Schematic of defect detection of double shadow method with reflected bulk waves at different positions (a, b, c, d, e)

Fig. 2. (a) Schematic of the propagation path and mode-translation of LU bulk waves; (b) simulated diagram of ultrasonic field

Fig. 3. Relationships between the arrival time and W of multi-modes ultrasonic waves in 30 mm thick aluminum plate obtained by (a) theoretical calculation and (b) finite element simulation

Fig. 4. Ultrasonic field simulation results of LU in aluminum plate. (a) Without defect; (b) containing defect with diameter of 0.8 mm

Fig. 5. (a) Experimental setup schematic for inspection of internal defects by LU; (b) X-ray DR image of the sample

Fig. 6. B-scanning figure obtained by LU scanning laser line source method

Fig. 7. Time domain waveforms of ultrasonic signals detected at different positions

Fig. 8. (a) Cross correlation coefficient curve of two ultrasonic signals obtained at different excitation positions; (b) fitting curve for calculating the wave velocity of surface acoustic wave

Fig. 9. (a) B-scanning figure of ultrasonic signals by TOF method; (b) waveforms obtained at positions with or without defect

Fig. 10. B-scanning figures detected at (a) the front-surface and (b) the bottom-surface of sample by double shadow method

Fig. 11. Time delay curves detected at (a) the front-surface and (b) the bottom-surface of sample by double shadow method

Fig. 12. Detection result of defect with 0.8 mm diameter using 10 MHz longitudinal wave transducer