Fig. 1. Diagram of experimental system. Illustration is diagram of reflected light from sample

Fig. 2. Diagram of scanning path by TOFD method

Fig. 3. B-scan image of ultrasonic signal obtained by TOFD method

Fig. 4. Time domain waveform obtained by heterolateral excitation and detection

Fig. 5. Diagram of line scanning path for contact surface

Fig. 6. Diagram of surface scanning path for contact surface

Fig. 7. Peak-to-peak values of direct longitudinal wave, direct transverse wave, and reflected longitudinal wave obtained at different scanning positions

Fig. 8. Peak-to-peak value of each modal signal at different propulsion distances

Fig. 9. Propagation paths of reflected longitudinal wave.(a) Detection after contact surface reflection; (b) detection after plano-convex lens plane reflection

Fig. 10. Average value of peak-to-peak values of longitudinal waves of nine points varies with propulsion distance in upper right corner of Fig. 8