Fabry-Perot Fiber Optic Sensors for Civil and Geotechnical Monitoring of Large Structures

Abstract

Miniature optical fiber sensors, based on Fabry-Perot technology, have found numerous applications in both patient monitoring and civil structural monitoring of large and massive infrastructures. Although structural health monitoring and patient monitoring may benefit from the unique advantages of optical fiber sensors (OFS) such as electromagnetic interferences (EMI) immunity, sensor small size and long term reliability, both applications are facing very different realities. This contribution presents the underlying sensing technology, the miniature sensor fabrication technique and numerous application examples in medical and civil engineering-fields. OFS for medical applications are single-point, measuring mainly parameters such as pressure or temperature. In the intra-aortic balloon pumping (IABP) therapy, a miniature OFS can monitor in situ aortic blood pressure to trigger catheter balloon inflation/deflation in counter-pulsation with heartbeats. Similar sensors reliably monitor the intracranial pressure (ICP) of critical care patients, even during surgical intervention or examinations under medical resonance imaging (MRI). Temperature OFS are also the ideal monitoring solution for such harsh environments. The same miniature sensing elements can be packaged differently to allow their use in civil and geotechnical monitoring. In particular, Fabry-Perot optical sensors have been in use for many years as direct replacement of conventional sensors based on the vibrating wire and other electrical technologies. Those sensors are ideal to measure strain, deformation, pressure and temperature in applications subject to strong electromagnetic fields, lighting strikes or requiring long cables. Application examples includes the monitoring of groundwater pressures in tailing dams used for mining applications in Chile, leaks in levees in The Netherlands and displacements in the cryogenically cooled superconducting magnets for ITER project in France.