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Study of Low-frequency FBG Vibration Sensor System

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Tutor: MengZhou LuoHong
School: National University of Defense Science and Technology
Course: Underwater Acoustics
Keywords: Low-frequency probe,Vibration sensor,FBG
CLC: TP212
Type: Master's thesis
Year:  2010
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Abstract:
Fiber Bragg grating (FBG) vibration sensor with high sensitivity , strong anti-jamming capability , good low-frequency detection performance , easily into the array reuse advantages the FBG sensing has become the new field of applied research . FBG vibration sensor demodulation system to achieve high performance for low frequency vibration signal detection theory analysis and simulation and experimental study , three different structure of the low-frequency FBG vibration sensor developed on this basis . First , through the method of analysis of the basic theory of FBG sensing technology and FBG vibration sensor design , design the metal drums encapsulated single cylinder mandrel type , the polyurethane encapsulated single cylinder mandrel type and double cylinder symmetrical push-pull mandrel - three sensor structure , and theoretical analysis and simulation . Accurate vibration sensor signal demodulation design and build a FBG vibration sensor demodulation system based on the unbalanced Michelson Interferometer PGC phase demodulation technology , and the demodulation system performance testing . The demodulation system is stable , the noise floor is less than - 90dB , the wavelength offset the minimum measured 3.8 ¡Á 10 ? 3pm, the dynamic strain the minimum detectable reach 3.2n¦Å . In order to improve the demodulation system stability and low-frequency demodulation capability , the structure of the double-grating sensor demodulation functions , this article is based on interferometry demodulation scheme to build a the Michelson interferometers double FBG demodulation system , through the dual match demodulation the technology can effectively reduce the system noise floor , the noise floor of the system below 200Hz reduced by approximately 10 dB . Finally, three different structures developed sensor experimental study . Mandrel type in which the metal drums package single cylinder FBG vibration sensor structure is simple , the natural frequency is 388Hz , applicable to low frequency vibration sensing below 200Hz , acceleration sensitivity to 80pm / g ; polyurethane encapsulated single cylinder mandrel type FBG vibration sensor high sensitivity , low-frequency detection performance , the natural frequency of about 155 Hz , applies to less than 100Hz low frequency vibration sensing acceleration sensitivity for 450pm / g ; the double cylinder symmetrical push-pull mandrel FBG vibration sensor with temperature compensation function high sensitivity and good low-frequency detection performance , high stability , good direction , simple structure , convenient extended to three-dimensional , etc. eigenfrequencies 210Hz sensitivity is approximately 450pm / g .
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