Optical fibre pressure sensors for small scale studies of groundwater flow

L. Coelho; N. Freitas; J. M. Baptista; O. Frazão; J. L. Santos; T. Restivo; J. Marques

doi:10.1117/12.891913

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26 July 2011 Optical fibre pressure sensors for small scale studies of groundwater flow

L. Coelho, N. Freitas, J. M. Baptista, O. Frazão, J. L. Santos, T. Restivo, J. Marques

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Proceedings Volume 8001, International Conference on Applications of Optics and Photonics; 80013V (2011) https://doi.org/10.1117/12.891913
Event: International Conference on Applications of Optics and Photonics, 2011, Braga, Portugal

Abstract

The underground movement of water through soil and rock is an important phenomenon in Civil Engineering. Its study is made more appealing to students if small scale prototypes are used, where several layouts of soil and water in steady state/transient conditions can be studied in detail. A water tank prototype was built with a reflective optical fibre pressure sensor based on a GRIN lens and a mirror. The mirror is connected to an elastic membrane that is deformed when water pressure is applied and the lens is correctly aligned with the mirror and fixed. The distance between the mirror and the lens changes, so the reflective optical power changes as well and it is directly proportional to the water pressure inside the tank. The results obtained for water pressure up to 4 kPa for filling and emptying operations show that the sensor has a linear response for pressure changes between 1.7 kPa and 3.4 kPa with a slope of 181 μW/kPa for filling and 191 μW/kPa for emptying. It is also observed some hysteresis that may possibly be reduced by choosing another material for the membrane. Using this type of sensor head it is possible to monitor different pressure points in the small scale prototype using the standard OTDR (Optical Time Domain Reflectometer) equipment.

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L. Coelho, N. Freitas, J. M. Baptista, O. Frazão, J. L. Santos, T. Restivo, and J. Marques "Optical fibre pressure sensors for small scale studies of groundwater flow", Proc. SPIE 8001, International Conference on Applications of Optics and Photonics, 80013V (26 July 2011); https://doi.org/10.1117/12.891913

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