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Publications

Publications by PHT

2015

Simultaneous measurement of strain and temperature based on clover microstructured fiber loop mirror

Authors
Perez Herrera, RA; Andre, RM; Silva, SF; Becker, M; Schuster, K; Kobelke, J; Lopez Amo, M; Santos, JL; Frazao, O;

Publication
MEASUREMENT

Abstract
In this work, two all-fiber loop mirrors using a clover microstructured fiber for the simultaneous measurement of temperature and strain are presented. The sensing heads are formed by a short piece of clover microstructured fiber with 35 mm and 89 mm length respectively. The geometry of the fiber allowed observing different interferences created by the microstructured fiber core section. Different sensitivities to temperature and strain were obtained and, using a matrix method, it is possible to discriminate both physical parameters. Resolutions of +/- 2 degrees C and +/- 11 mu epsilon for the first structure and +/- 2.3 degrees C and +/- 18 mu epsilon for the second one, for temperature and strain, respectively, were attained.

2015

Monitoring of high refractive index edible oils using coated long period fiber grating sensors

Authors
Coelho, L; Viegas, D; Santos, JL; de Almeida, JMMM;

Publication
OPTICAL SENSORS 2015

Abstract
Monitoring the quality of high refractive index edible oils is of great importance for the human health. Uncooked edible oils in general are healthy foodstuff, olive oil in particular, however, they are frequently used for baking and cooking. High quality edible oils are made from seeds, nuts or fruits by mechanical processes. Nevertheless, once the mechanical extraction is complete, up to 15% of the oil remains in oil pomace and in the mill wastewater, which can be extracted using organic solvents, often hexane. Optical fiber sensors based on long period fiber gratings (LPFG) have very low wavelength sensitivity when the surround refractive index is higher than the refractive index of the cladding. Titanium dioxide (TiO2) coated LPFG could lead to the realization of high sensitivity chemical sensor for the food industry. In this work LPFG coated with a TiO2 thin film were successfully used for to detect small levels of hexane diluted in edible oils and for real time monitoring the thermal deterioration of edible oils. For a TiO2 coating of 30 nm a wavelength sensitivity of 1361.7 nm/RIU (or 0.97 nm /% V/V) in the 1.4610-1.4670 refractive index range was achieved, corresponding to 0 to 12 % V/V of hexane in olive oil. A sensitivity higher than 638 nm/RIU at 225 degrees C was calculated, in the 1.4670-1.4735 refractive index range with a detection limit of thermal deterioration of about 1 minute.

2015

FIBER OPTIC DISPLACEMENT SENSOR BASED ON A DOUBLE-REFLECTING OTDR TECHNIQUE

Authors
Rocco Giraldi, MTMR; Fernandes, CS; Ferreira, MS; de Sousa, MJ; Jorge, P; Costa, JCWA; Santos, JL; Frazao, O;

Publication
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS

Abstract
In this work, it is proposed a technique to implement an intensity sensor based on the generation of a double-reflecting (ghost) signal in optical time domain reflectometry (OTDR). The intensity sensor is supported by a singlemode-multimode-singlemode (SMS) fiber structure combined with a fiber loop mirror (FLM). The results of the displacement sensitivity show linear behavior for both the first-reflecting and double-reflecting signals with linear slopes of approximately -4.5 dB/mm and -6 dB/mm, respectively. The displacement resolution achieved is approximate to 0.28 mm. It is also found that the system is able to read periodic displacement variations in the millisecond time scale applied to the sensing head. (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1312-1315, 2015

2015

Cryogenic Temperature Response of Reflection-Based Phase-Shifted Long-Period Fiber Gratings

Authors
Martins, R; Caldas, P; Teixeira, B; Azevedo, J; Monteiro, J; Belo, JH; Araujo, JP; Santos, JL; Rego, G;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
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.

2015

Polymeric Optical Fiber Tweezers as a tool for single cell micro manipulation and sensing

Authors
Rodrigues Ribeiro, RSR; Soppera, O; Guerreiro, A; Jorge, PAS;

Publication
24TH INTERNATIONAL CONFERENCE ON OPTICAL FIBRE SENSORS

Abstract
In this paper a new type of polymeric fiber optic tweezers for single cell manipulation is reported. The optical trapping of a yeast cell using a polymeric micro lens fabricated by guided photo polymerization at the fiber tip is demonstrated. The 2D trapping of the yeast cells is analyzed and maximum optical forces on the pN range are calculated. The experimental results are supported by computational simulations using a FDTD method. Moreover, new insights on the potential for simultaneous sensing and optical trapping, are presented.

2015

Fiber Optic Sensing System for Temperature and Gas Monitoring in Coal Waste Pile Combustion Environments

Authors
Viveiros, D; Ribeiro, J; Ferreira, J; Lopez Aldaba, A; Pinto, AMR; Perez Herrera, RA; Diaz, S; Lopez Gil, A; Dominguez Lopez, A; Esteban, O; Martin Lopez, S; Auguste, JL; Jamier, R; Rougier, S; Silva, SO; Frazao, O; Santos, JL; Flores, D; Roy, P; Gonzalez Herraez, M; Lopez Amo, M; Baptista, JM;

Publication
24TH INTERNATIONAL CONFERENCE ON OPTICAL FIBRE SENSORS

Abstract
It is presented an optical fiber sensing system projected to operate in the demanding conditions associated with coal waste piles in combustion. Distributed temperature measurement and spot gas sensing are requirements for such a system. A field prototype has been installed and is continuously gathering data, which will input a geological model of the coal waste piles in combustion aiming to understand their dynamics and evolution. Results are presented on distributed temperature and ammonia measurement, being noticed any significant methane emission in the short time period considered. Carbon dioxide is also a targeted gas for measurement, with validated results available soon. The assessment of this technology as an effective and reliable tool to address the problem of monitoring coal waste piles in combustion opens the possibility of its widespread application in view of the worldwide presence of coal related fires.

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