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

Resonant microbeams have been demonstrated to be sensitive strain transduce rs that can be used in pressure, acceleration, and temperature sensors. As high-Q strain-sensitive resonators, they can provide a frequency output rep resenting 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 mo dulated by the vibration of the microstructure. Treated as FM sources, they function as combined temperature and vibration sensors, with the average c arrier frequency las measured by a counter, for example) dependent on tempe rature and the FM demodulated signal providing the vibration spectrum. With properly designed acceleration-sensitive microstructures, low-noise la ser sources and detection electronics, and proper packaging, such devices c an provide high performance as both temperature sensors and vibration senso rs. As such, they may prove useful as structural health monitors or as moni tors for condition-based maintenance of rotating machinery. (C) 2000 Elsevi er Science S.A. All rights reserved.