High-Resolution Sensors for Mass Deposition and Low-Frequency Vibration Based on Phase-Shifted Bragg Gratings

This work presents high-resolution sensors based on phase-shifted Bragg gratings (PSBGs) for low-frequency vibrations monitoring and mass deposition sensing. We analyzed the reflected spectrum using a commercial interrogator for six values of deposited mass: 0, 0.22, 0.27, 0.32, 0.40, and 0.47 g. For the experimental data, a linear regression was calculated for PSBG 1 (R-2 = 0.9379 with a sensitivity of 0.0491 nm/g) and for uniform fiber Bragg grating (FBG) (R-2 = 0.909 with a sensitivity of 0.05182 nm/g). Machinery fault simulator (MFS) was used for the vibration monitoring setup for engine rotation frequency of 4-14 Hz in steps of 2 Hz. We used an alternative noncommercial interrogation system that consisted of a tunable laser, an optical circulator, an optical power acquisition board, and a prefixed phase-shifted Bragg. The proposed alternative interrogation system has the ability to center the tunable laser in the narrow valley region of the PSBG reflected spectrum, increasing the resolution for monitoring vibration at low frequencies. As a reference, the PSBG measurement results were compared with those of a piezoelectric accelerometer (PZT) fixed at the same bearing. For 4, 6, 8, 10, and 14 Hz, the relative error was 15%, 10%, 0%, 0%, and 1.43%, respectively. According to these results, PSBGs are a suitable option for monitoring low-frequency vibrations and for mass deposition sensing.