Study On Airflow Velocity Sensors Based On Cladding-Thinned Optical Fiber Bragg Gratings

Hot-wire optical fiber anemometers are used in many fields such as chemical engineering,aerospace industry,automotive industry and medical equipment technology because of its advantages of high sensitivity and large measurement range,but their sensitivity still needs to be improved.The initial temperature is a key parameter that affects the sensitivity of the sensor.This thesis focuses on the research of hot-wire anemometer based on fiber Bragg grating.The optimal coupling structure is designed through theoretical analysis and simulation optimization.By reducing the diameter of the fiber Bragg grating(FBG)and replacing the material of the film,the sensing performance of the anemometer is improved.The main contents are as follows:1.The research and development of optical fiber anemometers are reviewed.Interference fiber anemometers and fiber grating anemometers are introduced,and their sensing principles are explained.The hot-wire fiber grating anemometer based on different coupling structures and its sensing principle are introduced.Select the waistenlarged bitaper as a better structure.2.The sensor head of optical fiber is optimized and designed.By simulating the temperature of optical fiber with different diameters,we conclude that the optical fiber diameter is inversely proportional to the initial temperature.For the simulation of the coupling structure,we selected a lumbar width of 14 ?m and a length of 1 mm.3.A hot-wire anemometer based on cladding-thinned optical fiber Bragg grating is proposed.Its initial temperature is increased by?50%.The sensitivities obtained at different airflow velocities of 0.1,0.5,1.5,and 20 m/s were-1978,-443,-133,and-4.8 pm/(m/s).A significant improvement up to 61.2%in magnitude of sensitivity has been achieved.A new round of experiments was conducted focusing on the influence of FBG cladding thickness on the sensor performance to verify the correctness of the theory.4.A cladding-thinned FBG anemometer based on graphene-coated is proposed.Experiments were performed by replacing the silver layer with a graphene layer.The comparative experimental results show that the graphene-coated FBG anemometer has higher sensitivity than the silver-coated FBG anemometer.