A FBG-based, temperature-insensitive vibration sensor

Abstract

ABSTRACT In this paper, a novel temperature-insensitive vibration sensor based on a FBG is demonstrated. The FBG is glued in a slanted direction onto the lateral side of a right-angled triangle cantilever beam with an eccentric gear installed on its free end. Vertical vibration applied by the eccentric gear to the cantilever beam lead s to a uniform bending along the beam length. As a result, the FBG is chirped and its reflection bandwidth and power change periodically with the variation of the displacement of the free end. The experimental results we re compared with the data of vibration measurement of a conventional electrical strain sensor. Furthermore, this sensor is temperature insensitive, owning to the temperature-independence nature of reflection bandwidth and power of the FBG. Keywords : Vibration, Fiber Bragg grating, cantilever beam, temperature insensitive measurement. 1. INTRODUCTION Fiber Bragg gratings (FBGs) have attracted considerable interests in various fiber-optic sensor implementations for the past two decades. Sensing occurs through the monitoring of the variation in the reflection peak wavelength of the FBG. The reflection peak wavelength varies with the changes of the grating period and/or the effective index of the fiber core. The changes depend on the local ambient temperature and/or the strain field applied to the FBG. The sensitivity of the FBGs’ tuning variability and potential uses of the device have been studied by numerous groups. In addition to the well-known advantages of fiber-optic sensors such as electrically passive operation, immunity to RFI and EMI, high sensitivity, compact size and potentially low co st, FBG-based sensors have an inherent self-referencing capability and are easily multiplexed in a serial fashion along a single fiber. The success of FBG-based sensors on the measurement of strain has facilitated the modification of trans ducer designs that can deal with other measurands such as vibration [1-6]. Most of previously reported vibration sens ors relied on the demodulation of reflection wavelength shift, but the wavelength shift is sensitive to temperature. Additional temperature compensation techniques are therefore necessary, which add to syst em cost and complexity. In this paper, a novel temperature-insensitive vibration sensor based on a strain-chirped FBG is proposed. The FBG is glued in a slanted direction onto the latera l side of a right-angled triangle cantileve r beam with an eccentric gear installed on its free end. Vertical vibration app lied by the eccentric gear to the cantileve r beam leads to a uniform bending along the beam length. As a result, the FBG is chirped and its reflection bandwidth and power change periodically with the variation of the displacement of the free end. Besides, this sensor is temperature insensitiv e, owning to the temperature-independence nature of reflection bandwidth and power of the FBG.