Abstract: The feasibility of producing a practical buried fiber optic sensor with high sensitivity for detecting intruders is demonstrated. Experiments were carried out on such an all fiber Michelson interferometer in which the sensing arm was buried in sand. When a 42 inch sensing arm was buried 8 inches deep in sand, the weight required for a half fringe shift in the sensor output was 22 pounds and the sensitivity was about 10 degrees/pound. The relation between the applied pressure and the phase change was linear. Experimental results indicated that the sensitivity of an optical fiber sensor was sufficient to detect people on foot and vehicles passing over the buried fiber. !8
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