Fig. 1. Principle of time reversal self-focusing^[2]. (a) Single-array emission; (b) multi-array reception; (c) acoustic beam self-focusing

Fig. 2. Layout of virtual gain time reversal method^[9]

Fig. 3. Diagram of ultrasonic scanning imaging

Fig. 4. Diagram of multi-element synthetic aperture focused imaging

Fig. 5. Phased array. (a) Diagram of phased array focusing; (b) diagram of phased array deflection

Fig. 6. Results of phased array imaging and TR-MUSIC imaging^[14]. (a) Phased array imaging; (b) TR-MUSIC imaging

Fig. 7. Comparison of imaging results^[23]. (a) Imaging of TRIS; (b) imaging of traditional TR

Fig. 8. Imaging comparison of three algorithms^[29]

Fig. 9. Numerical simulation of ultrasonic interactions with defects in solids

Fig. 10. Picture of piezoelectric transducer

Fig. 11. Diagram of laser ultrasound in solids. (a) Thermoelastic mechanism; (b) ablation mechanism

Fig. 12. Laser ultrasonic detection principle for rail^[48]

Fig. 13. Variation of velocity with the temperature^[52]. (a) Velocity of longitudinal wave; (b) velocity of transverse wave

Fig. 14. Laser ultrasonic through air and water^［55］

Fig. 15. OmniScan X3 device

Fig. 16. A1040MIRA device

Fig. 17. Laser ultrasonic visualizing inspector^[61]

Fig. 18. Diagram of visualization principle of laser ultrasonic visualizing inspector ^[61]