A Rugged Fiber Optic Pressure Sensor for Underground Water Level Monitoring

Pressure sensors have many fields of application, ranging from environmental monitoring to the oil and gas industry. Different fiber optic sensors have been proposed for pressure measurement, but either they have small sensitivity, and hence are befitted for large pressure ranges, or they are based on interferometry, and hence require rather expensive laser sources. In this work, we present a rugged FBG sensor prototype capable of measuring underground water level with high sensitivity. The sensor exploits a 3D-printed highly-efficient mechanical transducer that converts external pressure in longitudinal strain along the fiber. The intrinsic temperature cross-sensitivity is compensated by the additional FBG embedded in the sensor. The structure is enclosed in an aluminum alloy case to withstand harsh environments and installation procedures. Pressure and temperature sensitivities of the sensor are about 20 pm / cm H 2 O and 17 pm/°C, respectively. The sensor has been designed to monitor the stability of dikes and embankments, by measuring the underground water level at their foot to detect anomalous filtration.