Fiber-optic vibration sensor based on frequency modulation of light-excited oscillators

Abstract

Resonant microbeams have been demonstrated to be sensitive strain transducers that can be used in pressure, acceleration, and temperature sensors. As high-Q strain-sensitive resonators, they can provide a frequency output representing the variable being sensed. This paper describes vibration sensors, a new application for optically self-resonant microbeam oscillators that are driven and sensed by a single multimode optical fiber. When fabricated into acceleration-sensitive microstructures, the oscillator frequency is modulated by the vibration of the microstructure. Treated as FM sources, they function as combined temperature and vibration sensors, with the average carrier frequency (as measured by a counter, for example) dependent on temperature and the FM demodulated signal providing the vibration spectrum. With properly designed acceleration-sensitive microstructures, low-noise laser sources and detection electronics, and proper packaging, such devices can provide high performance as both temperature sensors and vibration sensors. As such, they may prove useful as structural health monitors or as monitors for condition-based maintenance of rotating machinery.