Fig. 1. Analytical object and model of landmine’s multi-modal vibration characteristics. (a) Anti-tank plastic landmine; (b) equivalent cylindrical thin circular plate

Fig. 2. Contour diagrams of landmine mode shapes. (a) (0,1) mode; (b) (0,2) mode; (c) (1,1) mode

Fig. 3. Vibration deformation schematic diagram of the soil surface with and without landmine under the excitation of sound waves

Fig. 4. The optical path of laser speckle interferometry measurement on the mode shapes of the landmine’s upper casing

Fig. 5. Vibration diagram under (0,1) mode. (a) Three-dimensional vibration mode diagram; (b) contour map

Fig. 6. Vibration diagram under (0,2) mode. (a) Three-dimensional vibration mode diagram; (b) contour map

Fig. 7. Vibration displacement gradient change under the (0,1) mode. (a) Three-dimensional diagram of the displacement gradient change; (b) contour map

Fig. 8. Vibration displacement gradient change under the (0,2) mode. (a) Three-dimensional diagram of displacement gradient change; (b) contour map

Fig. 9. Mine modal shapes based on speckle interference fringes. (a) Under the (0,1) mode; (b) under the (0,2) mode

Fig. 10. Acousto-optic mine detection experimental system based on laser speckle measurement

Fig. 11. (a) The type-69 plastic case coach mine in dry sand. Bessel fringes obtained with different excitation sound frequencies and different sound pressure levels. (b) 110 Hz, 100 dB; (c) 110 Hz, 95 dB; (d) 110 Hz, 90 dB

Fig. 12. Bessel fringes of the type-69 plastic case coach mine in wet sand with different excitation sound frequencies and different sound pressure levels. (a) 110 Hz, 100 dB; (b) 110 Hz, 95 dB; (c) 110 Hz, 90 dB

Fig. 13. (a) Type 72 anti-personnel coach mine, and it’s Bessel fringes obtained with different excitation sound frequencies and different sound pressure levels. (b) 145 Hz, 100 dB; (c) 145 Hz, 98 dB; (d) 145 Hz, 95 dB

Fig. 14. (a) Brick in dry sand and (b) it’s speckle interferometer detection results obtained with the excitation sound frequency of 145 Hz and the sound pressure level of 100 dB

Fig. 15. Vibration amplitude of the type-69 plastic case coach mine in dry sand with the excitation sound frequency of 110 Hz and the sound pressure level of 100 dB. (a) Three-dimensional vibration; (b) contour map