Numerical Study on Strain Measurements Using the Improved Bonding Fiber Bragg Grating

This study suggests an improved bonding method for a surface mounted fiber grating strain sensor to significantly reduce the mechanical influences from the surrounding cement of a glued fiber grating in the conventional bonding method. The linear relationship between the voltage signals and the average strains within the glue-free fiber grating is the advantage of the improved bonding method over the conventional bonding method (distributing cement along the full fiber grating). The numerical computations based on the coupled-mode theory were conducted to obtain the reflection spectra of a fiber grating, that are induced from different strain fields. The one-dimensional strain fields, that vary linearly within a fiber grating, were considered in this research. In addition, the filtered spectral power interrogation system to obtain the voltage signals from an optical fiber framework was taken in consideration. The filtered spectral power interrogation system is economic, compact, and suitable for on site measurements compared with other systems such as the optical spectrum analyzer. For a glued fiber grating, results show that the distortions in shape and the dilations in area of its reflection spectrum are because of the varied strain gradients within the grating during a strain history. Also, the central wavelength shifts of a reflection spectrum are related to the average strains within a fiber grating. In applications using the improved bonding fiber grating strain sensor, its linear relationship between the voltage signals and the average strains shows the feasibility of obtaining calibrations by using a commonly used resistance strain gauge.