Research On Multi-core Fiber Flow Velocity And Flow Direction Measurement Technology

With the rapid growth of Chinese marine economy and the gradual implementation of the strategy of building a maritime power,it is extremely important to develop and utilize water resources and monitor the hydrological environment.Hydrological motion monitoring is one of the core applications of sensing technology.As a hot research topic,multi-core fiber gratings have the characteristics of uniform material,high integration and the same thermal expansion coefficient.The multi-core fiber grating sensor has anti-electromagnetic interference,excellent electrical insulation,corrosion resistance,compact structure,constant core position,small size and light weight.In this paper,we write Bragg gratings of different wavelengths on multi-core fibers and design a sensor that can measure curvature and direction of force simultaneously.It can be applied in fluid environment to realize the simultaneous measurement of velocity and direction of flow,and eliminate the influence of ambient temperature on experimental measurement.The specific research contents are as follows:Firstly,the development and application of multi-core fiber grating sensing technology are introduced,and the current common hydrological flow direction sensors are analyzed.Based on the coupled mode theory,the principle of multi-core fiber Bragg grating sensing is analyzed,and the common fiber grating demodulation technology is introduced.Secondly,multi-core fiber Bragg gratings with different wavelengths are maded in ultraviolet exposure method by selecting suitable multi-core fiber and single-mode fiber connection methods.Making curvature sensor through the research on the packaging method of multi-core fiber grating sensor and designing water flow direction sensor lay the foundation for the following sensing experiment.Thirdly,through the analysis the multi-core fiber Bragg grating curvature measurement and direction determination sensing principle,design a dual-core Bragg grating sensing structure that can simultaneously measure curvature and direction,simulate and analyze the sensing structure and experimental demonstration.The results show that it is sensitive to both curvature and direction of force.The curvature and the direction of the force can be simultaneously measured by the wavelength change.Finally,the study of temperature and stress sensing of multi-core fiber Bragg grating overcomes the problem of temperature and stress cross-sensitivity in practical continuous measurement application.The sensor is applied to the measurement of liquid velocity and flow direction,which has high practical value.