A Fiber Bragg Grating–Based Inclinometer Fabricated Using 3-D Printing Method for Slope Monitoring

A new temperature-insensitive inclinometer was fabricated using a 3-D printing method based on fiber Bragg grating (FBG) sensors. This new tilt sensor is characterized by its light weight, immunity to electromagnetic interference (EMI) small size, quick prototyping, and cost effectiveness. FBG sensors were directly inscribed into polylactic acid, which was also used for fabricating all different parts of tilt sensors. Calibration tests of this new tilt sensor were performed in laboratory to examine its measurement performance. Measurement sensitivity of 0.012 nm/° and a maximum tilt angle of 25° of the FBG inclinometer was approached in the calibration experiment. The measured tilt angles were validated by theoretical angles calculated in terms of all physical parameters of internal functional parts of the inclinometer. A monitoring test of a sandy slope model using this new tilt sensor was conducted in laboratory. Finite element analysis was also used to examine the mechanical behavior of the slope model under different loading levels. Monitoring test results indicate that the FBG-based tilt sensor presented no obvious change before a surcharge load approaching 0.245 kN but exhibited step-by-step rise in tilt angle afterward, achieving a maximum tilt angle of around 6°. Horizontal displacement, which was calculated in terms of the tilt sensor at different loading levels, was found to agree fairly well with the displacement data from both finite element analysis and displacement transducers.