Study On Strain Transfer Characteristics Of Fiber Bragg Grating Sensors

Fiber Bragg Grating (FBG) sensor is a passive device which has some specific characteristics such as immune to electromagnetic interference, long transmission distance, easy to implement large-scale distributed measurement by using wavelength division multiplexing, time division multiplexing and space division multiplexing technologies. Therefore, in recent years, FBG sensors have been demonstrated for measurement of a wide variety of fields, such as civil engineering, petrochemical engineering, advanced aircraft and space vehicles, the electrical power industry, and also being attractive for monitoring in explosive and high electromagnetic environments. However, due to the poor resisting shear ability and being very fragile in nature, bare fiber should be bonded onto the measured structures directly or encapsulated into a certain structure with adhesives while in practical applications. Due to the different mechanical properties of the bare fiber, the coating layer, the adhesive layer and the host material, the strain measured by bare fiber would be different from that of the measured host material, and packaging technologies have a significant influence on strain transfer characteristics of FBG sensors.The paper primarily researches on FBG strain sensors. The strain transfer characteristics of FBG sensors are analyzed with finite element method, and the influencing factors are discussed, which are verified by experiments. The influences of packaging technologies to strain transfer characteristics of FBG sensors are studied by experiments. Sensing characteristics of FBG at cryogenic temperature are investigated as well. The main content is:1. Generally introducing the development and the applications of FBG sensors, as well as the present state of strain transfer theories.2. Sensing principle and strain transfer theories of FBG sensors are analyzed, finite element method is employed for analyses of strain distribution and the influencing factors of strain transferring, which are verified by experiments.3. One FBG sensor bonded onto a polymer substrate is presented, which possess high strain transfer efficiency and easy to be bonded to implement large-scale distributed measurements. The influences of packaging technologies to strain transfer characteristics of FBG sensors are studied by experiments, including encapsulation material, adhesives and bonded lengths.4. The chirping mechanism of FBG at cryogenic temperature is studied, and the sensing characteristics of FBG sensor bonded onto a polymer substrate are investigated with the experiments employed at liquid nitrogen temperatures.