Impact of embedding techniques in FBG sensors

Embedded fiber Bragg gratings (FBGs) have been fabricated for use as pressure sensors to measure forces applied in the direction perpendicular to the fiber axis. The 1 cm length acrylate-coated FBGs were embedded into fiber-reinforced composites in two orientations in separate samples to test the properties of pressure sensor in each case. In samples where the FBG is embedded in parallel to the carbon fiber, the reflected spectrum remains a single wavelength peak as expected from an FBG. However, for samples where the FBG is placed at 90deg to the carbon fiber, peak split was observed. Scanning electron microscopy (SEM) of the embedded acrylate-coated fiber shows that the FBG embedded parallel to the carbon fiber is wrapped completely while the FBG embedded at 90deg to the carbon fiber is difficult to be wrapped well, suggesting the existence of longitudinal inhomogeneity