Cantilever Type Accelerometer Based on a Mirror-Terminated Hetero-Core Optical Fiber

Abstract

This paper describes a novel cantilever type accelerometer using a mirror-terminated hetero-core optical fiber for fault diagnosis of machinery. Hetero-core optical fiber sensors are suitable for long-term measurement in on-site fields with attractive advantages of robustness to environmental disturbances such as electromagnetic interference, chemical corrosion, and temperature fluctuation. Moreover, the proposed sensor contained a mirror termination on the hetero-core fiber in order to form a compact and cantilever-shaped structure. It was experimentally found that the mirror-terminated hetero-core fiber worked as Mach-Zehnder interferometry having interference fringes in transmission spectrum, in which linear changes in peak intensities enabled to detect the deflection of fiber beam using a cost-effective LED/PD measurement instrument. For the vibration response characteristics, the sensor reproduced the waveforms of input vibrations to optical loss changes when sinusoidal vibration was applied. Furthermore, the sensitivities were stable in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.4\times10^{3}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.3\times10^{2}$ </tex-math></inline-formula> dB/g for the frequency ranges less than 620–130 Hz, when setting a fiber beam length by 6–13 mm. Additionally, finite element simulations indicated that the frequency response characteristics were well correlated with the vibration characteristics of the cantilever-shaped fiber beam, which implied that the sensor performance can be optimized with respects to the sensitivity and the measurable frequency range by changing the fiber beam length.