Cookies
O website necessita de alguns cookies e outros recursos semelhantes para funcionar. Caso o permita, o INESC TEC irá utilizar cookies para recolher dados sobre as suas visitas, contribuindo, assim, para estatísticas agregadas que permitem melhorar o nosso serviço. Ver mais
Aceitar Rejeitar
  • Menu
Publicações

Publicações por Luís Carlos Coelho

2017

New developments on fibre optic colorimetric sensors for dissolved CO2 in aquatic environments

Autores
Coelho, L; Pereira, C; Mendes, J; Borges, T; de Almeida, JMMM; Jorge, PAS; Kovacs, B; Balogh, K;

Publicação
OCEANS 2017 - ABERDEEN

Abstract
The detection of dissolved carbon dioxide (dCO(2)) is made possible through a colorimetric effect that occurs in a sensitive membrane. The reaction with dCO(2) changes the pH of the membrane causing a small difference in its colour which results in a characteristic absorbance spectrum band near 435 nm. A sensing platform based on this effect was developed and tested in gaseous and in aqueous environments. It is a combination of a bundle of large core fibre optics (with diameters above 200 mu m) with light emission diodes (LEDs) in the visible range of the spectrum, a silicon photodetector and a polymer membrane sensitive to CO2. A variation in the absorption of 3 / %VV was obtained in the range from 0 to 1.6 % of gaseous CO2 with an estimated response time below 60 seconds.

2018

Plasmonic Optical Fiber Sensor Based on Double Step Growth of Gold Nano-Islands

Autores
de Almeida, JMMM; Vasconcelos, H; Jorge, PAS; Coelho, L;

Publicação
SENSORS

Abstract
It is presented the fabrication and characterization of optical fiber sensors for refractive index measurement based on localized surface plasmon resonance (LSPR) with gold nano-islands obtained by single and by repeated thermal dewetting of gold thin films. Thin films of gold deposited on silica (SiO2) substrates and produced by different experimental conditions were analyzed by Scanning Electron Microscope/Dispersive X-ray Spectroscopy (SEM/EDS) and optical means, allowing identifying and characterizing the formation of nano-islands. The wavelength shift sensitivity to the surrounding refractive index of sensors produced by single and by repeated dewetting is compared. While for the single step dewetting, a wavelength shift sensitivity of similar to 60 nm/RIU was calculated, for the repeated dewetting, a value of similar to 186 nm/RIU was obtained, an increase of more than three times. It is expected that through changing the fabrication parameters and using other fiber sensor geometries, higher sensitivities may be achieved, allowing, in addition, for the possibility of tuning the plasmonic frequency.

2018

Photoelectron extraction efficiency into Ar-CF4 and Xe-CF4 gas mixtures

Autores
Escada, J; Coelho, LCC; Dias, THVT; Lopes, JAM; dos Santos, JMF;

Publicação
JOURNAL OF INSTRUMENTATION

Abstract
Experimental measurements of the extraction efficiency f of the photoelectrons emitted from a reflective CsI photocathode into Ar-CF4 and Xe-CF4 gaseous mixtures are presented, as a function of reduced electric field E/p in the range 0.1 to 3 V cm(-1) Torr(-1) and as a function of CF4 concentration. The experimental data is compared to Monte Carlo simulation results. The investigation confirms that backdiffusion of low-energy photoelectrons emitted from a photocathode into a gas medium depends strongly on the nature of the gas. The effect is especially significant in pure noble gases, but it can be considerably reduced by the admixture of certain molecular gases, like CF4.

2018

Development of a new system for real-time detection of radon using scintillating optical fibers

Autores
Monteiro, CS; Coelho, L; Barbosa, SM; Guimarães, D;

Publicação
Optics InfoBase Conference Papers

Abstract
A remote sensor for radon continuous measurement using polymeric scintillation optical fibers was developed and evaluated. Successful preliminary results showed detection of natural occurring radon from a container with rocks rich in uranium oxides. © OSA 2018 © 2018 The Author(s)

2018

Low-cost interrogation system for long period fiber gratings as sensing devices

Autores
Dos Santos P.S.S.; Jorge P.A.S.; De Almeida J.M.M.M.; Coelho L.;

Publicação
Optics InfoBase Conference Papers

Abstract
A system with fiber laser diodes and photodetector replaces the usual bulky and expensive systems for characterization of long period fiber gratings and high correlation is achieved when measuring refractive index, temperature and curvature.

2018

Optical fiber sensor Mach-Zehnder interferometer based on TiO<inf>2</inf> coated long period fiber grating

Autores
Vasconcelos H.; De Almeida J.M.M.M.; Jorge P.A.S.; Coelho L.;

Publicação
Optics InfoBase Conference Papers

Abstract
The wavelength sensitivity and spectral resolution of Mach-Zehnder fiber interferometers based on uncoated and TiO2 coated LPFGs is presented and compared with TiO2 coated single LPFGs optical fiber sensors.

  • 8
  • 27