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Monitoring of Structure Characteristics, Humidity, Temperature and Torsion Using Optical Fiber Sensor

Esmailzadeh Noghani, Fereshteh | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52510 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Bahrampour, Alireza; Tofighi, Sara
  7. Abstract:
  8. Fiber optic sensors have found industrial applications due to their unique characteristics and wide range of environmental parameters. Specifically, distributed optical fiber sensors which have applications in borders protection, intrusion detection, oil and gas leakage detection and smart irrigation of farms and gardens, have attracted significant attention from research groups around the world in recent years. According to the forecasts, among all kind of optical fiber sensors, the temperature and acoustic/vibration sensors will seize the market during the coming years. In this thesis, three kind of optical fiber sensors are proposed for environment health monitoring. First, distributed optical fiber sensor with sub-centimeter spatial resolution, short measurement time and kilometer dynamic range is introduced. In this method, a train of sub-nanosecond pulses is sent into the fiber to excite the acoustic wave sequentially. The results show that since the intensity ratio of successive Stokes pulses depend on the Brillouin frequency, the local temperature/strain information can be extracted by measuring this intensity without the need for evaluating the Brillouin gain. No the need for scanning causes the measurement time is reduced. In the next, we investigate distributed humidity optical fiber sensor. In this sensor, the optical fiber is coated by humidity sensitive and insensitive polymers periodically and is surrounded by stainless steel. Water molecules absorption by humidity sensitive polymers causes swelling and inducing the strain in the optical fiber. The results show the refractive index modulation due to strain which is proportional to relative humidity is realized by optical time domain reflectometer. At the end, optical fiber torsion sensor base on computer-generated-hologram is investigated. In this sensor, the flex ural mode is excited using acoustic wave in suitable frequency. This results in fiber refractive index modulation and coupling of fundamental mode to the other mode of double mode fiber. Applying torsion to double mode fiber causes the rotation of these two mode profiles. The results show the contribution of each mode in the output field is obtained by using computer generated-hologram with proper interference patterns and photodetectors and so one can measure the twist angle
  9. Keywords:
  10. Temperature Sensor ; Rayleigh Scattering ; Simulated Brillouin Scattering (SBS) ; Computer Generated Hologram ; Torsion Sensor ; Humidity Sensor ; Distributed Optical Fiber Sensor

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