Research On Key Technologies Of Distributed Fiber Temperature/ Dynamic Strain Sensing

Distributed optical fiber sensors have attracted many scholars' interest because of their outstanding advantages such as fully distributed detection along an optical fiber,high accuracy,long-range sensing,resistance to electromagnetic interference,cost-effectiveness,etc.In the past decades,distributed optical fiber sensors have been widely used in structural health monitoring,such as oil and natural gas,and perimeter intrusion monitoring.The amplitude,phase,polarization and wavelength of the transmitted signal in the fiber will be modulated by the external temperature,strain,vibration,etc.We can achieve these physical parameters sensing by a series of demodulation algorithms.Compared with traditional single-point sensors,fiber sensors have a fully distributed detection because of fibers not only act as transmission media but also have sensing function.Temperature and strain are crucial parameters in many physical measurements.In this paper,the methods of temperature and vibration distributed measurement are studied in detail,including temperature measurement,vibration measurement and simultaneous measurement of temperature and vibration.The main content of the thesis includes:(1)In recent years,the research progress of temperature-strain dual-parameter optical fiber sensors is introduced in this paper,including point-type and distribution.The advantages and disadvantages of each sensor and its main performance are analyzed and summarized.(2)The basic principles of temperature distributed measurement based on Raman scattering is studied.And the corresponding calculation formula is deduced.According to its sensing principle,appropriate devices are selected to build the temperature sensing system.Finally,we achieve the temperature measurement in a 1.3 km single-mode fiber with the spatial resolution of 3m and the measurement error of ±0.6 ??(3)The dynamic strain distributed measurement method based on Rayleigh scattering of single mode fibers is studied.The principle of ?-OTDR is mainly studied,including the modulation and demodulation of phase.Finally,distributed vibration measurements with a broadband range of 0.2 Hz-20 kHz and stress measurements with a sensitivity of 0.007 rad / n? and a resolution of 27 n? have been realized through corresponding experiments.(4)A high-precision distributed temperature/dynamic strain dual-parameter distributed optical fiber sensing method based on backscatter enhanced optical fiber is studied.Backscatter enhanced optical fiber is used as sensing fiber to improve the signal-to-noise ratio of the sensing system.Combined with the technology of ?-OTDR,a suitable filter is designed according to the different frequency band of static temperature and dynamic strain to realize the synchronous measurement of two parameters.Finally,a temperature/dynamic strain dual-parameter sensor system is built to verify the synchronous distributed measurement ability of distributed temperature/dynamic strain.Especially,the system can realize highly sensitive distributed temperature measurement in a small-scale sensing area only 10 cm long,and can accurately detect ultra-low frequency dynamic strain at 0.01 Hz.The detection signal-to-noise ratio of distributed dynamic strain is 18.1dB higher than the ?-OTDR system based on single-mode optical fiber.