Design And Study Of Liquid Temperature And Pressure Sensor Based On Distributed Optical Fiber Sensing Technology

Distributed optical fiber sensing technology is the main technology of modern optical sensing,which is widely used in various engineering fields,such as monitoring of oceans,oil wells and dams.To achieve the effect of high-precision liquid temperature and pressure measurement,the sensor needs to be sensitized.To achieve a high-reliability measurement target,it is necessary to make the liquid temperature and pressure directly act on the sensing fiber and protect the sensing fiber to avoid the influence of the complex liquid environment on the measurement,so the encapsulation of the optical fiber is particularly important.This thesis solves the problems encountered in the practical process by combining theory and simulation experiments.The main research contents involved are liquid temperature and pressure sensor design and simulation,theoretical analysis and finite element simulation of surface-mounted optical fiber sensor strain transfer,and the effect of optical fiber winding on the performance of optical fiber sensor.In this thesis,the types and principles of scattering in optical fibers are firstly introduced,the sensing mechanism and development history of distributed optical fiber sensors based on three scattering effects are expounded,and the functional expressions between Brillouin frequency shift and temperature and strain are deduced.It lays a theoretical foundation for this work.For distributed fiber optic sensors,it is necessary to protect the fiber when measuring liquid temperature and pressure,while maintaining the advantages of high repeatability and corrosion resistance of the sensor.In this thesis,a thin-walled cylindrical liquid temperature and pressure sensor is designed,and the influence of the sensor material parameters and structural parameters on the temperature and pressure sensing characteristics of the sensor is analyzed through simulation.The simulation results show that when 316 L stainless steel is selected as the sensor material,the minimum thickness of the sensor cylinder wall is 0.6 mm,the diameter is 25 mm,the pressure sensitivity is 6.37 MHz/MPa,and the temperature sensitivity is 2.5 MHz/℃.When C17200 beryllium bronze is selected as the sensor material,the minimum thickness of the sensor cylinder wall is 0.5 mm,the diameter is 25 mm,the pressure sensitivity is 11.1 MHz/MPa,and the temperature sensitivity is 2.56 MHz/℃.Compared with ordinary single-mode fiber,there is a great improvement,which provides a theoretical basis for sensor design.To make the sensitivity of the designed liquid temperature and pressure sensor closer to the real situation,the average strain transfer efficiency of the thin-walled cylindrical surface-mounted fiber optic sensor was analyzed.The effect of the sensor model physical parameters on the average strain transfer efficiency was analyzed using finite element simulation software,the sensor model physical parameters including not only the upper thickness,lower thickness,Young’s modulus,and Poisson’s ratio of the adhesive layer but also the coating layer’s Young’s modulus and Poisson’s ratio.The simulation results are consistent with the theoretical analysis results.Finally,the optical power loss caused by the winding diameter and winding pitch is analyzed experimentally,and the Brillouin scattering intensity and the Brillouin scattering spectrum changes caused by the winding method are measured by using the existing frequency-shifted local heterodyne BOTDR system in the laboratory.