Polymer optical fiber sensors in human life safety

The current state of research into polymer optical fiber (POF) sensors linked to safety in human life is summarized in this paper. This topic is directly related with new solutions for civil aircraft, structural health monitoring, healthcare and biomedicine fields. In the last years, the properties of polymers have been explored to identify situations offering potential advantages over conventional silica fiber sensing technology, replacing, in some cases, problematic electronic technology used in these mentioned fields, where there are some issues to overcome. POFs could preferably replace their silica counterparts, with improved performance and biocompatibility. Finally, new developments are reported which use the unique properties of POF

Time-dependent variation of POF Bragg grating reflectivity and wavelength submerged in different liquids

In this work, we investigate the time-dependent variation of both the reflectivity and resonance wavelength of microstructured polymer optical fiber Bragg grating (mPOFBG) array sensors embedded in silicone rubber and polyurethane resin diaphragms in contact with water and aircraft fuel, respectively. The array sensors were inscribed using two different phase masks with pitches of 557.5 and 580 nm and the thermal annealing of the inscribed fiber was used to change the Bragg wavelengths. Both the reflection and the resonance wavelength shift were monitored over 90 days submerged in liquid and two studies were investigated. In the first study, in addition to the mPOFBGs coated with the diaphragm, also the rest of the fiber is totally protected between the sensors with the same material used for diaphragms. On the other hand, in the second study, the fiber between sensors is unprotected – in direct contact with liquid. PMMA and TOPAS fibers were used and this study suggests that TOPAS fiber should be a good option for long-term liquid monitoring applications

Annealing and etching effects on strain and stress sensitivity of polymer optical fibre Bragg grating sensors

Thermal annealing and chemical etching effects on the strain and stress sensitivity of polymer optical fibre based sensors are investigated. Bragg grating sensors have been photo-inscribed in PMMA optical fibre and their strain and stress sensitivity has been characterised before and after any annealing or etching process. The annealing and etching processes have been tried in different sequence in order to investigate their impact on the sensor’s performance. Results show with high confidence that fibre annealing can improve both strain and stress sensitivities. The fibre etching can also provide stress sensitivity enhancement, however the strain sensitivity changes seems to be random

Multi-objective water allocation in the Alqueva Region

Alqueva dam in the Alentejo Region was developed to solve water scarcity in the South ofPortugal and to ensure pennanent availability ofwater for household and industrial consumption, irrigation, production of electric energy, ecological and environrnental purposes. Competition among some ofthese multiple water uses requires an integrated management framework. This paper uses Interactive Decision Maps (IDM) technique to explore and achieve efficient and equitable water allocation combinations taking into account those multipIe goals and principIes of good water govemance. Results show that multiple water uses do constrain full economic impact for agriculture and suggest that integrated management frameworks and policies are needed at regional territoriallevel to reach a compromise between competing economic, social and environrnental goals and achieve project global development benefits

Acousto-optic modulation in a microstructured plastic optical fibre Bragg grating

The present work addresses the control of the mPOF Bragg grating spectrum properties through acousto-optic modulation. For the first time, the interaction of a flexural acoustic wave, generated by longitudinal excitation of different frequencies, with the Bragg grating will be presented. Also it will be demonstrated the quasi linear relationship between PZT load and maximum reflected power/ 3dB bandwidth of the reflected spectrum

Aviation fuel gauging sensor utilizing multiple diaphragm sensors incorporating polymer optical fiber Bragg gratings

A high-performance fuel gauging sensor is described that uses five diaphragm-based pressure sensors, which are monitored using a linear array of polymer optical fiber Bragg gratings. The sensors were initially characterized using water, revealing a sensitivity of 98 pm/cm for four of the sensors and 86 pm/cm for the fifth. The discrepancy in the sensitivity of the fifth sensor has been explained as being a result of the annealing of the other four sensors. Initial testing in JET A-1 aviation fuel revealed the unsuitability of silicone rubber diaphragms for prolonged usage in fuel. A second set of sensors manufactured with a polyurethane-based diaphragm showed no measurable deterioration over a three month period immersed in fuel. These sensors exhibited a sensitivity of 39 pm/cm, which is less than the silicone rubber devices due to the stiffer nature of the polyurethane material used

High performance liquid-level sensor based on mPOFBG for aircraft applications

A high performance liquid-level sensor based on microstructured polymer optical fiber Bragg grating (mPOFBG) array sensors is reported in detail. The sensor sensitivity is found to be 98pm/cm of liquid, enhanced by more than a factor of 9 compared to a reported silica fiber-based sensor

Fiber-optic liquid level monitoring system using microstructured polymer fiber Bragg grating array sensors:performance analysis

A highly sensitive liquid level monitoring system based on microstructured polymer optical fiber Bragg grating (mPOFBG) array sensors is reported for the first time. The configuration is based on five mPOFBGs inscribed in the same fiber in the 850 nm spectral region, showing the potential to interrogate liquid level by measuring the strain induced in each mPOFBG embedded in a silicone rubber (SR) diaphragm, which deforms due to hydrostatic pressure variations. The sensor exhibits a highly linear response over the sensing range, a good repeatability, and a high resolution. The sensitivity of the sensor is found to be 98 pm/cm of water, enhanced by more than a factor of 9 when compared to an equivalent sensor based on a silica fiber around 1550 nm. The temperature sensitivity is studied and a multi-sensor arrangement proposed, which has the potential to provide level readings independent of temperature and the liquid density

Sensitivity enhancement using annealed polymer optical fibre based sensors for pressure sensing applications

Thermal annealing can be used to induce a permanent negative Bragg wavelength shift for polymer fibre grating sensors and it was originally used for multiplexing purposes. Recently, researchers showed that annealing can also provide additional benefits, such as strain and humidity sensitivity enhancement and augmented temperature operational range. The annealing process can change both the optical and mechanical properties of the fibre. In this paper, the annealing effects on the stress and force sensitivities of PMMA fibre Bragg grating sensors are investigated. The incentive for that investigation was an unexpected behaviour observed in an array of sensors which were used for liquid level monitoring. One sensor exhibited much lower pressure sensitivity and that was the only one that was not annealed. To further investigate the phenomenon, additional sensors were photo-inscribed and characterised with regard their stress and force sensitivities. Then, the fibres were annealed by placing them in hot water, controlling with that way the humidity factor. After annealing, stress and force sensitivities were measured again. The results show that the annealing can improve the stress and force sensitivity of the devices. This can provide better performing sensors for use in stress, force and pressure sensing applications

Determination of the radial profile of the photoelastic coefficient of plastic optical fibers

We developed a measurement method to determine the radial distribution of the photoelastic coefficient C(r) in step-index polymer optical fibers (POFs). The method is based on the measurement of the retardance profile of a transversally illuminated fiber for increasing tensile load. The radial profile C(r) is obtained from the inverse Abel transform of this retardance profile. We measured polymer fibers from different manufacturers. The radial profile of the photoelastic constant can considerable vary depending on the type and treatment of POFs, even when made from similar materials, which leads to the conclusion that the photoelastic constant should be characterized for each different type of POF. The impact of annealing the fiber samples on C(r) is also addressed