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de interesse
Detalhes

Detalhes

  • Nome

    Luís Carlos Coelho
  • Cargo

    Investigador Auxiliar
  • Desde

    01 fevereiro 2010
008
Publicações

2024

Impact of gaseous interferents on palladium expansion for hydrogen optical sensing: A time stability study

Autores
Almeida, MAS; Almeida, JMMMD; Coelho, LCC;

Publicação
OPTICS AND LASER TECHNOLOGY

Abstract
Continuous monitoring of hydrogen (H2) concentration is critical for safer use, which can be done using optical sensors. Palladium (Pd) is the most commonly used transducer material for this monitoring. This material absorbs H2 leading to an isotropic expansion. This process is reversible but is affected by the interaction with interferents, and the lifetime of Pd thin films is a recurring issue. Fiber Bragg Grating (FBG) sensors are used to follow the strain induced by H2 on Pd thin films. In this work, it is studied the stability of Pd-coated FBGs, protected with a thin Polytetrafluoroethylene (PTFE) layer, 10 years after their deposition to assess their viability to be used as H2 sensors for long periods of time. It was found that Pd coatings that were PTFE-protected after deposition had a longer lifetime than unprotected films, with the same sensitivities that they had immediately after their deposition, namely 23 and 10 pm/vol% for the sensors with 150 and 100 nm of Pd, respectively, and a saturation point around 2 kPa. Furthermore, the Pd expansion was analyzed in the presence of H2, nitrogen (N2), carbon dioxide (CO2), methane (CH4) and water vapor (H2O), finding that H2O is the main interferent. Finally, an exhaustive test for 90 h is also done to analyze the long-term stability of Pd films in dry and humid environments, with only the protected sensor maintaining the long-term response. As a result, this study emphasizes the importance of using protective polymeric layers in Pd films to achieve the five-year lifetime required for a real H2 monitoring application.

2024

Optical pH Sensor Based on a Long-Period Fiber Grating Coated with a Polymeric Layer-by-Layer Electrostatic Self-Assembled Nanofilm

Autores
Pereira, JM; Mendes, JP; Dias, B; de Almeida, JMMM; Coelho, LCC;

Publicação
SENSORS

Abstract
An optical fiber pH sensor based on a long-period fiber grating (LPFG) is reported. Two oppositely charged polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), were alternately deposited on the sensing structure through a layer-by-layer (LbL) electrostatic self-assembly technique. Since the polymers are pH sensitive, their refractive index (RI) varies when the pH of the solution changes due to swelling/deswelling phenomena. The fabricated multilayer coating retained a similar property, enabling its use in pH-sensing applications. The pH of the PAA dipping solution was tuned so that a coated LPFG achieved a pH sensitivity of (6.3 +/- 0.2) nm/pH in the 5.92-9.23 pH range. Only two bilayers of PEI/PAA were used as an overlay, which reduces the fabrication time and increases the reproducibility of the sensor, and its reversibility and repeatability were demonstrated by tracking the resonance band position throughout multiple cycles between different pH solutions. With simulation work and experimental results from a low-finesse Fabry-Perot (FP) cavity on a fiber tip, the coating properties were estimated. When saturated at low pH, it has a thickness of 200 nm and 1.53 +/- 0.01 RI, expanding up to 310 nm with a 1.35 +/- 0.01 RI at higher pH values, mostly due to the structural changes in the PAA.

2024

Observation of Surface Plasmon Polaritons and Bloch Surface Waves in a Metal-Dielectric Photonic Crystal

Autores
Dias, BS; De Almeida, JMMM; Coelho, LCC;

Publicação
IEEE Sensors Journal

Abstract

2023

Refractometric sensitivity of Bloch surface waves : perturbation theory calculation and experimental validation

Autores
Dias, BS; De Almeida, JMMM; Coelho, LCC;

Publicação
OPTICS LETTERS

Abstract
The sensitivity of one-dimensional Bloch surface wave (BSW) sensors to external refractive index variations using Kretschmann's configuration is calculated analytically by employing first-order perturbation theory for both TE and TM modes. This approach is then validated by com- parison with both transfer matrix method simulations and experimental results for a chosen photonic crystal structure. Experimental sensitivities of (8.4 +/- 0.2)x102 and (8.4 +/- 0.4)x102 nm/RIU were obtained for the TE and TM BSW modes, corresponding to errors of 0.02% and 4%, respectively, when comparing with the perturbation the- ory approach. These results provide interesting insights into photonic crystal design for Bloch surface wave sensing by casting light into the important parameters related with sen- sor performance.(c) 2023 Optica Publishing Group

2023

Compact biosensor system for the quantification of hydrogen peroxide in milk

Autores
Vasconcelos, H; Matias, A; Mendes, J; Araujo, J; Dias, B; Jorge, PAS; Saraiva, C; de Almeida, JMMM; Coelho, LCC;

Publicação
TALANTA

Abstract
Hydrogen peroxide is usually added to products to delay the development of microorganisms mainly in milk, hence increasing its stability over time, however the side effects can become devastating to human health.A technique is presented consisting of detecting hydrogen peroxide as an adulterant in milk through a sensor where pretreatment of the sample is not necessary, using a single use membrane. The detection of hydrogen peroxide in fresh-raw, whole, semi-skimmed and skimmed milk was performed using a luminol chem-iluminescence reaction.For hydrogen peroxide water solutions, a linear response was attained from 1.0 x 10-4 to 9.0 x 10-3 %w/w and an LOD (limit of detection) of 3.0 x 10-5 %w/w was determined. An R-squared value of 0.97 and a relative standard deviation lower than 10%, were achieved.Hydrogen peroxide concentration as low as 1.0 x 10-3 %w/w was measured for fresh-raw, skim and whole milk and for semi-skimmed milk, as low as 2.0 x 10-3 %w/w.The methodology presented, as long as our knowledge, is original, rapid, ecological and inexpensive. In regard of the sensitivity obtained, the methodology has great possibility to be applied in the detection of hydrogen peroxide in several areas. It is envisaged monitoring of food quality, agriculture systems and environment pollution.

Teses
supervisionadas

2022

Wireless optical fibre sensors network for the health monitoring of concrete structures

Autor
Pedro Miguel Madeira da Silva

Instituição

2022

Listening for wolf conservation: Deep learning for automated howl recognition and classification

Autor
Rafael de Faria Campos

Instituição
UP-FCUP

2022

Electromagnetic Surface Waves in One Dimensional Structures: Application to Optical Sensors

Autor
Bernardo Manuel Limpo Serra dos Santos Dias

Instituição
UP-FCUP

2021

Filogenia mitogenomica de bivalves de água doce (Bivalvia: Unionida)

Autor
João Eduardo Afonso Teiga Teixeira

Instituição

2020

Development of cost-effective monitoring systems for chemical water contamination using nanoparticle coated optical fibre sensors

Autor
Paulo Sérgio Soares dos Santos

Instituição
UP-FEUP