Enhanced PDMS-embedded FBG devices for displacement sensing

In recent years, the importance of reliable displacement detection for structural condition monitoring has grown significantly for applications requiring high-sensitivity devices to meet the diverse needs of various applications, ranging from millimeters to micrometers. This study focuses on fabricating and characterizing three polydimethylsiloxane (PDMS) based devices designed for displacement detection through curvature variation, each incorporating an embedded fiber Bragg grating (FBGs). These devices comprise a solid piece, one with three central perforations (hollow) and another with three notches (notched), that allow greater deformation in the structure, which implies greater sensitivity. A comprehensive assessment was conducted for various displacement and temperature conditions. Because embedded FBGs experience tensile or compressive deformations contingent on the bending direction of the devices, they demonstrate a wider measurement range without compromising sensitivity. One of the most notable findings of this study is the heightened sensitivity observed in hollow and notched devices compared with solid devices. Incorporating these geometric variations facilitates stress concentration owing to the curvature changes. In a simultaneous evaluation, the three devices were subjected to millimetric and micrometric displacements, which allowed the evaluation of individual parameters such as curvature and displacement sensitivity, in addition to temperature sensitivity, hysteresis errors, linearity, and repeatability of the measurements. The Solid device has a sensitivity of 112.7 pm/mm, while the perforated and notched devices show higher sensitivities of up to 159.5 pm/mm and 162.7 pm/mm, respectively. This represents increases of 41.5 % and 44.36 %, respectively. This study contributes to the advancement of displacement sensing technologies and offers practical solutions for various structural monitoring applications.