Strain transfer mechanism of quadrate-packaged FBG sensors embedded in rectangular structures

Fiber Bragg grating (FBG)-based sensors have been increasingly used to measure the strain of structures. For the material characteristic of optical fiber, FBG is usually clad with protective coatings in practical engineering. Existence of the protective layer absorbs a portion of strain of the monitored structure and contributes to the strain transfer error. To correct this error and improve the testing accuracy, theoretical analysis on strain transfer mechanism of a three-layered mechanical model with quadrate-packaged FBG sensor embedded in rectangular structure is conducted in this paper. Numerical simulation is adopted to verify the correctness and laboratory tests are planned to validate the effectiveness of the proposed strain transfer formula. Sensitivity of geometrical and material parameters that influence the strain transfer efficiency and optimum analysis is studied. Results indicate that the proposed strain transfer mechanism is feasible to modify the strain transfer error and improve the testing accuracy of the sensor embedded in rectangular structure, and sensitive parameters and optimum design are provided as well for the better use of FBG sensors in engineering.