Study On Optical Fiber Bragg Grating Based Anemometers

Abstract:Compared with traditional sensors, fiber optic sensors have many advantages, such as immunity to electromagnetic interference, resistance to corrosion, compact, and high sensitivity. In this paper, we combined with the optical fiber sensing technology and flow measurement principle together to carry out a new study of the flow sensor based on fiber Bragg grating (FBG). The main contents are as follows:1, The general situation of fiber sensors and the development of fiber anemometer are introduced. Fiber grating fabrication system in our lab is introduced. And the sensing principle of FBG is investigated.2, An intensity-modulated anemometer by using a biconical optical fiber taper incorporating with a FBG is proposed. The light reflected by the FBG passes twice through the fiber taper, whose insertion loss is tuned by the tested airflow through airflow velocity-dependent fiber bending. High sensitivity of 0.315μW/(m/s) and resolution of 0.042 m/s are achieved within a measurement range up to 6.57 m/s.3, A novel anemometer based on a silver-coated FBG is proposed and experimentally demonstrated with the assistance of a short length of no-core fiber (NCF). The silver coating deposited on the surface of the FBG absorbs light of a pump laser, which is coupled into the fiber cladding by the NCF, to generate the heat, whereas air flow cools down the FBG by taking the heat away. A dynamic thermal equilibrium with a temperature codetermined by the pump laser power and airflow velocity can be reached. Bragg wavelength of the FBG changes with temperature thus is used to measure airflow velocity. Experimental results reveal that the resolution of 0.003 m/s and the sensitivity of 333.3 pm/(m/s) is achieved at the airflow velocity of 0.5m/s, respectively, and the measurement range covers 0-13.7 m/s.4, A fiber hot-wire anemometer based on an optical fiber bitaper and a silver-coated FBG is demonstrated for airflow velocity measurement. The bitaper with an enlarged waist diameter shows high and stable coupling efficiency, and it has enhanced mechanical strength than a normal fiber so that high airflow velocity measurement is possible. Experimental results show that a large measurement range up to 13.7 m/s is realized, and at the airflow velocity of 0.5m/s, respectively, the sensitivity and resolution of up to 1000 pm/(m/s) and 0.001 m/s.