This paper presents a low frequency fiber optic accelerometer for application in high temperature environments of civil engineering structures. The reflection-based extrinsic fiber optic accelerometer developed in this study consists of a transmissive grating panel, reflective mirror, and two optical fiber collimators as the transceiver whose function can be maintained up to 130°C. The dynamic characteristics of the sensor probe were investigated and the correlation between the natural frequency of the sensor probe and temperature variation was described and discussed. Furthermore, high temperature simulation equipment was designed for the verification test setup of the developed accelerometer for high temperature. This study was limited to consideration of 130°C applied temperature to the proposed fiber optic accelerometer due to an operational temperature limitation of commercial optical fiber collimator. The sinusoidal low frequency accelerations measured from the developed fiber optic accelerometer at 130°C demonstrated good agreement with that of an MEMS accelerometer measured at room temperature. The developed fiber optic accelerometer can be used in frequency ranges below 5.1？Hz up to 130°C with a margin of error that is less than 10% and a high sensitivity of 0.18？(m/s2)/rad. 1. Introduction Over the past three decades, many types of fiber optic accelerometers (FOAs) have been developed because optical fibers (OFs) allow structural health monitoring within highly electromagnetic environments .Furthermore, optical fiber with fused silica is useful in a wide temperature range up to about 1000°C  although it depends on the optical fiber material such as fused silica and sapphire (Al2O3, single crystal alumina) [3, 4]. While most intensity-based fiber optic sensor systems are relatively low cost, fiber Bragg grating (FBG) sensor systems are rather higher cost wavelength shift interrogation equipment for high speed sampling frequency rates. Alternatively, intensity modulation techniques have been conducted on grating-based extrinsic type fiber optic sensors (FOSs) [5–7] because the grating-based sensors [8, 9] possess significant advantages : simple mechanical structure and good reliability, among others. Therefore, research on grating-based fiber optic sensors has been conducted based on the shutter effect [9, 11] or the Moiré phenomenon techniques , which require four optical fiber lines and two grating panels. However, these transmission type FOSs [6, 7, 9, 11], including the Moiré fringe-based FOA, depending on the transmitted light
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