Development of ultrasound guided optical fiber sensors

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Recently, fiber-optic sensors have seemed promising sensors for structural health monitoring because of their electromagnetic interference immunity, small size as well as lightweight. Conventional fiber-optic ultrasonic sensors, such as fiber Bragg grating sensor and interferometric fiber optic sensors are based on the optical characteristic modulation induced by ultrasonic perturbation and the sensing part is directly bonded to the materials to be monitored.In the present study, we focused on the superior ultrasonic guide characteristics of optical fibers. Optical fiber was bonded to the monitored specimen. Ultrasound propagated through the specimen was caught by the optical fibers bonded to the specimen and ultrasound propagated along the optical fiber was detected with fiber Bragg grating or piezoelectric sensor. First, we have studied basic characteristics of optical fibers on ultrasonic propagation not only experimentally but also analytically. Second, we have developed resonant fiber-optic ultrasonic sensors by devising the installation of optical fiber to the tested specimen. Then, we have applied fiber-optic ultrasonic guide sensors to ultrasonic non-destructive testing of metallic materials. Fiber-optic ultrasonic guide sensors have been demonstrated enough sensitivity of ultrasonic detection to detect defects in metallic materials.Fiber-optic ultrasonic guide sensors can be candidate sensors which are applied to harsh environment such as elevated temperature.