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Tafulo P.A.R.,INESC Porto | Jorge P.A.S.,INESC Porto | Santos J.L.,INESC Porto | Santos J.L.,University of Porto | And 3 more authors.
IEEE Sensors Journal | Year: 2012

Two Fabry-Pérot interferometers based on chemical etching in multimode graded index fibers are fabricated and their response to temperature and strain are compared. Chemical etching is applied in the graded index fiber end creating an air cavity. The interferometric cavity is formed when the graded index fiber with the air concavity is spliced to a single-mode fiber. The intrinsic sensors present high sensitivity to strain and low sensitivity to temperature. For the 62.5 μm core fiber, sensitivities of 6.99 pm/με and, 0.95 pm/°C were obtained for strain and temperature, respectively. The sensor based in the 50 μm core fiber, on the other hand, presented sensitivities of 4.06 pm/με and -0.84 pm/°C for strain and temperature, respectively. © 2006 IEEE.

Viegas D.,INESC Porto | Viegas D.,University of Porto | Hernaez M.,Public University of Navarra | Goicoechea J.,Public University of Navarra | And 5 more authors.
IEEE Sensors Journal | Year: 2011

A novel configuration able to measure simultaneously relative humidity and temperature is proposed. The sensing head is based on a long-period fiber grating (LPG) coated with silica nanospheres in-line with a fiber Bragg grating. The polymeric overlay that changes its optical properties when exposed to different humidity levels is deposited onto the LPG using the electrostatic self-assembly technique (ESA), resulting into a humidity-induced shift of the resonance wavelength of the LPG. Considering the humidity range from 20% to 50% RH, a system resolution of 1.6% RH and 2.5 °C was achieved. At higher humidity, from 50% to 80% RH, the corresponding resolution values were 2.4% RH and 0.4 °C. © 2010 IEEE.

Martins R.,INESC Porto | Martins R.,Polytechnic Institute of Viana do Castelo | Martins R.,University of Porto | Caldas P.,INESC Porto | And 12 more authors.
Journal of Lightwave Technology | Year: 2015

In this study, we investigated the temperature behavior of phase-shifted long-period fiber gratings (PS-LPFGs) inscribed in two types of optical fiber: B/Ge and SMF28. The experiments were carried out from 5 to 305 K using a superconducting quantum interference device magnetometer. The average temperature sensitivity obtained of -0.43 nm/K for PS-LPFGs inscribed in the B/Ge fiber is one order of magnitude larger than for PS-LPFGs inscribed in the SMF28 fiber, in the 60-240 K range. Values ranging from -0.08 nm/K up to 0.2 nm/K were obtained in the 5-35 K temperature range, which are considerably better than previous results achieved for metal-coated FBGs and also for LPFGs inscribed in a similar B/Ge codoped fiber. Nevertheless, further work is required in order to correctly address sensor reliability. © 2014 IEEE.

Agency: Cordis | Branch: FP7 | Program: JTI-CS | Phase: JTI-CS-2009-1-GRA-01-011 | Award Amount: 78.00K | Year: 2010

Fiber Bragg grating sensors (FBG) for structural health monitoring has gained increasing importance in aerospace applications, since it enables large-scale measurement of most relevant structural parameters while mitigating well-know technical constrains of conventional sensors. The main drawback of a fiber Bragg grating strain sensor is its thermal cross-sensitivity. Currently such a single parameter measurement is difficult to implement, since cross-sensitivity to temperature compels the use of an additional temperature reference. In this project a passive athermal FBG strain gage that renders optional the measurement of temperature is proposed. Such a design will benefit large scale system design and performance. The innovative design will ensure athermal operation of the strain gage by canceling the intrinsic fiber optic thermal sensitivity. Moreover the passive athermal design may be adjusted to further compensate for structural thermal expansion, thus enabling stress and load-induced strain-components to be measured. Special care will be taken on the design of the sensor enclosure to enable multiplexing of several sensors over a single optical fiber and ease installation procedures in aerospace applications. Qualified space fiber optic cables for sensing network deployment will be employed. Commercially available industrial interrogation unit equipment will be taken as a base to evaluate the optoelectronic hardware adaptation that would be required in order to fulfill aerospace specifications. The design requirements will be assessed in terms of mechanical (mass, volume, vibration and shock), thermal (heat dissipation and operation temperature range) and electrical parameters (power consumption and communication interface). Embedded software will allow for data conversion from wavelength measurements to engineering parameters (strain, temperature, load) that will afterwards be processed considering SHM requirements to provide automatic alarm generation.

Agency: Cordis | Branch: FP7 | Program: JTI-CS | Phase: JTI-CS-2009-1-GRA-01-012 | Award Amount: 80.00K | Year: 2010

The objective of this activity is to design and manufacture composite specimens integrating fibre optic sensors, evaluate the reliability of the sensors, develop a concept to evaluate the system reliability and define a design of experiments of sensorized structures. The purpose of this study is to facilitate the validation of real-time health monitoring systems, which can detect strain as well as the temperature of the structure at multiple locations through numerous embedded optical fibre sensors. Optical fibre sensors for damage detection will be embedded in the structure made of carbon fibre reinforced plastic (CFRP) composite laminates. An integrated assessment of all critical manufacturing steps of fibre Bragg grating strain sensors will be performed in order to achieve high reliability of the embedding process in composite materials. The study will comprise the analysis of different types of optical fibres towards the optimization of embedding processes in composite materials. High resolution strain mapping by embedding series of closely spaced independent sensors in composite material samples will be assessed. Parameters that influence the infant failure of the structures will be analysed and the tests required to asses their effect will be defined. A preliminary test campaign based on thermal, mechanical and fatigue tests have already been defined.

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