Biaxial FBG Vibration Sensor With a Single Edge Filter and Matching Demodulation

This work developed, simulated, and characterized a high sensitivity vibration sensor for low-frequency applications. The fiber Bragg grating (FBG) overlapping method was used to demodulate the wavelength shift of the sensing gratings, but only one FBG for each axis was utilized (unlike two FBGs in the common approach), along with another one acting as a filter for both axes and temperature compensator; this enhanced method could measure acceleration in two axes simultaneously, although only the X-axis had constant sensibility in the entire operating range. The difficulty in achieving constant sensitivity in both axes lies in the need to match three Bragg gratings, resulting in a set of gratings with similar Bragg wavelengths. The new results showed constant sensitivity in both accelerometer axes (0.735 and 0.684
$\text{V}\cdot \text{m}^{-1}\cdot \text{s}$
2 for the X- and Y-axis, respectively). The usable frequency and acceleration amplitude ranges were from 0.5 to 20 Hz and from
$14\times10$
−3 to 9 m/s2, respectively, which both meet the requirements for detecting seismic-induced movements. Furthermore, the present results demonstrate that we can utilize a smaller number of gratings in accelerometer development compared to the common approach.