Mingli Dong

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.

Error assessment of helicoidal surfaces

Helicoidal surfaces are very useful in many aspects, their error assessment has become more and more important. In this paper, studied the method of the error assessment, and the key point was focused on how much number of measuring points to be enough. Firstly, the current methods of the error assessment were analyzed. Then, the study was spread out from general equation of the helicoidal surfaces to general model of the error and the error assessment, and pointed out the number of the measuring points could be determined with the variations of the means and the variances of the errors. Finally, took a worm as an example to explain that the method is feasible.