الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Fiber Bragg grating based acoustic sensors are very important nowadays as they have many different applications. They have many advantages over conventional electronic acoustic sensors. They used in military, economical, and civil applications. They are not only sensitive to acoustic waves, but also are sensitive to other measurands. In this report, we study fiber Bragg gratings as acoustic sensors. Fundamentals and effects of acoustic wave on fiber Bragg gratings are presented. Some of interrogation detection methods are simulated. These methods are matched filter and DWDM detection methods in addition to linear edge source detection method. Three structures of FBGs (UFBG, πFBG, and CFBG) are studied and a comparison between them is illustrated. πFBG is simulated using two UFBG with a phase shift between them. By simulating 2 cm πFBG, it gives a spectral response with a bandwidth equals to the bandwidth of 20 cm UFBG and that is one of the comparison points. As the chirp parameter of CFBG increases, the spectral response of it becomes broaden. CFBGs of 0, 0.2, and 0.6 nm chirp parameter are simulated. The effects of the grating length, refractive index modulation depth, and the ultrasonic frequency on the sensitivity of these three structures are presented. At the last, FBG hydrophone with rubber diaphragm and FBG with metal diaphragm are presented. As the young’s modulus of the diaphragm increases, the sensitivity of the hydrophone enhances. Using phase shift FBG hydrophone increases the sensitivity by 20dB compared with the uniform FBG hydrophone.