Fig. 1. Fiber Bragg grating based ultrasonic sensor with coupling cone structure. (a) Schematic diagram; (b) physical map

Fig. 2. Simulated dynamic response of coupling cone excited by ultrasonic wave

Fig. 3. Schematic of sideband filtering based FBG demodulation

Fig. 4. Temporal responses of the proposed ultrasonic sensor with different FBG lengths for 150-kHz continuously sinusoidal ultrasonic wave. (a) FBG length is 2 mm; (b) FBG length is 10 mm; (c) FBG length is 15 mm; (d) FBG length is 20 mm

Fig. 5. Peak-to-peak values of the proposed ultrasonic sensor with different FBG lengths at different ultrasonic wave frequencies

Fig. 6. Experimental setup of ultrasonic nondestructive detection system

Fig. 7. Lamb wave signals under different hole-size defects detected by FBG sensing system. (a) 10 mm; (b) 13 mm; (c) 18 mm; (d) 20 mm

Fig. 8. Spectral response of Lamb wave under different hole-size defects

Fig. 9. Amplitudes of S₀ and A₀ modes under different hole-size defects