Comparison of Metal-Packaged and Adhesive-Packaged Fiber Bragg Grating Sensors

A feasible metallic packaging technique of fiber Bragg grating (FBG) sensors is developed for measurement of strain, and it can be simply achieved via one-step ultrasonic welding. The strain transfer coefficient of the FBG sensor is theoretically evaluated by a proposed model aiming at determining the proper packaging parameters of a surface-bonded FBG sensor. According to analytical results, the metallic packaging shows higher strain transfer coefficient compared with traditional adhesive packaging under the same conditions. Comparisons of the experimental results with the numerical predictions for the strain sensitivity show a satisfactory agreement. Experimental strain tests are performed on an elaborate uniform strength beam for both tensile and compressive strain, and the strain sensitivity of ~1.26 and 1.34 pm/με is obtained for the tensile and compressive situation, respectively. The results of comparison demonstrate that the metal-packaged FBG sensor has a certain advantage in respect of strain measurement in specific sensing field, such as long-term, high-precision, and harsh-environment structural health monitoring.