Structural Health Monitoring using Apodized Pi-Phase Shifted FBG: Decoupling Strain and Temperature Effects

摘要

Fiber Bragg Gratings (FBGs) as tools for structural health monitoring are broadly used for assessing the composite structures behavior under different scenarios to secure the system in a reliable and accurate way. Due to cross-sensitivity effects in optical sensors, one way to enhance the accuracy is to disentangle the strain from other affecting parameters such as temperature or vibration for recognizing the real strain that is experienced by the composite structure. In this work, design and numerical simulations of Apodized Pi-Phase Shifted FBG (π-PSFBG) are presented to evaluate the performance of non-uniform FBG for simultaneous strain and temperature monitoring. Due to specific accuracy and spectral characteristics of the π-PSFBG, it is selected as an optical sensor to enhance the sensitivity of the measurements. Sensor signals are designed and simulated by solving coupled mode equations using the transfer matrix to represent the reflection spectrum of π-PSFBG. To accomplish spectral improvement, the Gaussian apodization function is applied to the FBG reflected spectrum in order to optimize its spectra by suppressing side lobes. Moreover, we have developed π-PSFBG sensor using Neural Networks (NNs) approach to sense and discriminate strain from other affecting gauges such as temperature. The proposed neural networks is trained to learn the relationship between the reflection spectrum and the external parameters such as strain and temperature. Our investigations not only characterize the performance of an apodized π-PSFBG to simultaneously measure two parameters with high sensitivity, but also yield the minimum error in compensation of strain from temperature.