A Fiber-Only Optical Vibration Sensor Using Off-Centered Fiber Bragg Gratings

Vibration monitoring of rotating machinery is crucial for operational safety and optimized maintenance. In this work, we propose a fiber Bragg grating (FBG) vibration sensor that does not involve any other components beyond the optical fiber on which the FBG is inscribed. The optical fiber is supported at one end to form a cantilever arrangement. The FBG is positioned at the support, intentionally offset from the center of the fiber core. Continual bending of the cantilever beam due to vibration induces axial tensile and compressive stresses away from the neutral axis, where the off-centered FBG is located. This causes a reciprocating shift in the FBG's central wavelength, enabling us to measure the frequency and amplitude of the applied vibration. Since central wavelength is the measurand, the proposed sensor is compatible with wavelength division multiplexing, thereby expanding its utility across diverse industries. The sensor prototype fabricated and tested in this study, performed linearly within a wide range of frequencies (20–1500 Hz), and was responsive to accelerations as low as 0.3 g. The sensor characteristics can be tailored to a specific application by fine-tuning the dimensions and support configurations.