Responses of Fiber Grating Ultrasound Sensors and Development of a Sensing System
Dr. Ching-Chung Yin
|Keywords:||光柵光纖;超音波;感測系統;fiber grating;ultrasound;sensing system|
The thesis investigates responses of fiber Bragg grating sensors due to ultrasound and reports the experience in development of a sensing system. The influences resulted from various coupling conditions between optic fibers and the plate-like host materials as well as their corresponding manufacturing problems are reported. A fiber optic sensing system includes a broadband light source, interferometer-based fiber optic sensors, demodulation devices, optic detectors, and so on. In the experiment, laser-induced plate waves and acoustic bulk wave were impinged upon one fiber grating sensor mounted on the surface of a carbon/epoxy composite plate and another embedded in a plate made of acrylic resin. Wavelength of the reflected light from fiber grating is dynamically changed once upon the pitches of Bragg grating are disturbed by the incident acoustic waves. The infinitesimal shift in optical fiber wavelength is demodulated to phase change using an unbalanced Mach-Zehnder fiber optic interferometer. The demodulation is performed near the quadrature point to keep a linear relationshop between the phase shift and light intensity output of the interferometer. Working principles of each fiber-optic device, various experimental setups and their results are discussed and commented.
|Appears in Collections:||Thesis|