Doppler effect-based fiber-optic sensor and its application in ultrasonic detection

Based on the Doppler effect of light wave transmission in optical fiber, Doppler effect-based fiber-optic (FOD) sensor possesses outstanding advantages in acquiring vibration/acoustic waves with high sensitivity. Furthermore, when shape of the FOD sensor was properly selected, its sensitivity was bonding direction-independent, namely non-directionality. In this paper, characteristics of the FOD sensor were investigated for the purpose of ultrasonic detection. A piezoelectric wafer was applied as an actuator to excite Lamb waves, a kind of ultrasonic wave, in an aluminum-alloy plate. Features of the ultrasonic wave signals, collected using a number of spiral FOD sensors with various inner diameters and outer diameters, were compared to investigate characteristics of FOD sensor. Amplitude curves of the FOD sensors were hereby obtained for the future applications in ultrasonic acquisition. The results demonstrated that sensitivity of the spiral FOD sensor with longer optical fiber length was higher than that with shorter fiber length.