Development of a tilt meter based on a hetero-core fiber optic sensor

This thesis proposes a newly developed tilt-meter by means of optical fiber hetero-core structured sensor. An optical fiber has advantages such as resistance to corrosion and electromagnetic interference. Additionally, the hetero-core optical fiber is sensitive to bending action only on the sensor portion and the fiber transmission line is unaffected to external disturbances such as temperature fluctuation because of its single-mode stable propagation scheme. Therefore, a hetero-core fiber sensor enables to monitoring harsh environment in a long time usage and is suited for landslide detection in various situations. The proposed tilt-meter consists of an aluminum balk, a pendulum with a weight and a bearing. The tilt can be converted into bending by a clamper at the pendulum and an aluminum board in the tilt-meter. The proposed tilt-meter has indicated a dynamic range of 4.57 dB for ±15 deg., which is needed to check landslide, and accuracy of ±1.5 deg. On the other hand, it was proposed that flat springs added in the tilt-meter so as to decrease hysteresis effect. As a result, the loss for full-scale was decreased to be 2.45 dB, however, the precision was improved to be ±0.2 deg.