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007
Publications

2018

Temperature Compensated Strain Sensor Based on Long Period Gratings and Microspheres

Authors
Ascorbe, J; Coelho, L; Santos, JL; Frazao, O; Corres, JM;

Publication
IEEE Photonics Technology Letters

Abstract

2018

Quantification of Ethanol Concentration in Gasoline Using Cuprous Oxide Coated Long Period Fiber Gratings

Authors
Monteiro Silva, F; Santos, JL; Marques Martins de Almeida, JMMM; Coelho, L;

Publication
IEEE Sensors Journal

Abstract

2018

Real-time Early Warning Strategies for Corrosion Mitigation in Harsh Environments

Authors
Costa Coelho, LCC; Soares dos Santos, PSS; da Silva Jorge, PAD; Santos, JL; Marques Martins de Almeida, JMMM;

Publication
Journal of Lightwave Technology

Abstract
Long period fiber gratings (LPFGs) were coated with iron (Fe) and exposed to oxidation in air and in water having different concentrations of sodium chloride (NaCl) to detect the formation of iron oxides and hydroxides. The process was monitored in real time by measuring the characteristics of the LPFGs attenuation bands. Thin films of Fe were deposited on top of silica (SiO2) substrates, annealed in air, and exposed to water with NaCl. The composition of the oxide and hydroxide layers were analyzed by SEM/EDS and XRD. It was observed the formation of oxide phases, Fe3O4 (magnetite) and Fe2O3 (hematite) when annealing in air, and Fe2(OH)3Cl (hibbingite) and FeO(OH) (lepidocrocite) when exposed to water with NaCl. Results shows that Fe coated LPFGs can be used as sensors for real time monitoring of corrosion in offshore and in coastal projects where metal structures made of iron alloys are in contact with sea or brackish water. In addition, LPFGs coated with hematite were characterized for sensing, leading to the conclusion that the sensitivity to the refractive index of the surrounding medium can be tuned by proper choice of hematite thickness. IEEE

2017

Monitoring of oxidation phases of copper thin films using long period fiber gratings

Authors
Coelho, L; Agostinho Moreira, JA; Tavares, PB; Santos, JL; Viegas, D; de Almeida, JMMM;

Publication
SENSORS AND ACTUATORS A-PHYSICAL

Abstract
Long period fiber gratings (LPFGs) were used to monitor the characteristics of copper (Cu) thin films when annealed in air atmosphere up to similar to 680 degrees C. The wavelength and the optical power shift of the resonant bands of the LPFGs when coated with the Cu thin films, were measured as a function of the annealing temperature, and were found to exhibit a different evolution comparing to a bare LPFGs. Thin films of Cu deposited on quartz (SiO2) substrates were annealed and analyzed by XRD, SEM/EDS and Raman spectroscopy, allowing to identify the formation of two distinct oxide phases at different temperatures, cuprous (Cu2O-cuprite) and cupric (CuO-tenorite) oxides, respectively. The observed features of the resonant bands of the LPFGs were found to be associated with the Cu oxide phase transitions, indicating the possibility of using LPFGs to monitor, in real time, the oxidation states of Cu thin films by following specific characteristics of the attenuation bands. In addition, LPFGs over coated with the two distinct oxidation phases of Cu were characterized for refractive index sensing in the range between 1.300 to 1.600, leading to the conclusion that the sensitivity to the refractive index of the surrounding medium of Cu coated LPFGs sensing systems can be temperature tuned.

2017

Study of corrosion using long period fiber gratings coated with iron exposed to salty water

Authors
Coelho, L; Santos, JL; Jorge, PAS; de Almeida, JMM;

Publication
2017 25TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS (OFS)

Abstract
A study of long period fiber gratings (LPFG) over coated with iron (Fe) and subjected to oxidation in water with different sodium chloride (NaCl) concentrations is presented. The formation of iron oxides and hydroxides was monitored in real time by following the features of the LPFG attenuation band. Preliminary results show that Fe coated LPFGs can be used as sensors for early warning of corrosion in offshore and in coastal projects where metal structures made of iron alloys are in contact with sea or brackish water.

Supervised
thesis

2016

Analysis of Plasmonics Based Fiber Optic Sensing Structures

Author
Hamed Moayyed

Institution
UP-FCUP

2016

Research and development of optical fibre sensors based on thin film coating technology

Author
Luís Carlos Costa Coelho

Institution
UP-FCUP

2015

Fiber Sensing Based on New Structures and Post-Processing Enhancement

Author
Marta Sofia dos Anjos Ferreira

Institution
UP-FEP