FISO Technologies (Canada)

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 different realities. This paper presents, with practical examples, several OFS technologies ranging from single-point to distributed sensors used to address the health monitoring challenges in medical and in civil engineering fields. OFS for medical applications are single-point, measuring mainly vital 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 interventions or examinations under medical resonance imaging (MRI). Temperature OFS are also the ideal monitoring solution for such harsh environments. Most of OFS for structural health monitoring are distributed or have long gage length, although quasi-distributed short gage sensors are also used. Those sensors measure mainly strain/load, temperature, pressure and elongation. <i>SOFO</i> type deformation sensors were used to monitor and secure the Bolshoi Moskvoretskiy Bridge in Moscow. Safety of Plavinu dam built on clay and sand in Latvia was increased by monitoring bitumen joints displacement and temperature changes using <i>SMARTape</i> and <i>Temperature Sensitive Cable </i>read with <i>DiTeSt</i> unit. A similar solution was used for monitoring a pipeline built in an unstable area near Rimini in Italy.

Changes observed in polarized light transmission through an anisotropic material, such as birefringent porous glass, upon contact with air bearing vapors of volatile organic compounds serve as the basis for a very sensitive broadband chemical sensor. When properly designed, vapor sensors based on such porous glasses show changes in transmitted light intensity or spectral content (color) detectable by eye. When placed between two crossed polarizers, the form-birefringent porous glass produces an observable phase shift that undergoes a readily detectable decrease upon exposure to all organic vapors we tested thus far. The optical effects resulting from exposure to vapors are reversible and believed to result from capillary condensation of solvent vapors and attendant reduction of anisotropy. A good control of the microporous structure as well of the surface chemistry offers flexibility for tuning the sensor response to VOC industrial applications. Simple sensor miniaturization with low cost materials is possible.

As opposed to other techniques’ using translating mirror to change the optical cavity length in response to a displacement, our transducer requires no alignment and no optical element to condition the light beam. Hence, it is very robust to various mechanical shocks and temperature variation.

Throughout the years, Bomem get involved in a number of state-of-the-art remote sensing projects from balloons, planes and satellites. MIPAS, a Michelson Interferometer for Passive Atmospheric Sounding is among the recent activities of Bomem. This paper will focus on several aspects of this device designed to measure concentration profiles of stratospheric constituents on a global scale. After this introduction, we present the purpose of MIPAS and its different subsystems. We list the specifications of MIPAS and discuss some details of its different parts. We finally look at the signal processing and the calibration of the instrument.