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Browsing CAP - Indexed Articles in Journals by Author "4678"
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    Acoustic Optical Fiber Sensor Based on Graphene Oxide Membrane
    ( 2021) Catarina Silva Monteiro ; Raposo,M ; Ribeiro,PA ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 6568
    A Fabry–Pérot acoustic sensor based on a graphene oxide membrane was developed with the aim to achieve a faster and simpler fabrication procedure when compared to similar graphene-based acoustic sensors. In addition, the proposed sensor was fabricated using methods that reduce chemical hazards and environmental impacts. The developed sensor, with an optical cavity of around 246 µm, showed a constant reflected signal amplitude of 6.8 ± 0.1 dB for 100 nm wavelength range. The sensor attained a wideband operation range between 20 and 100 kHz, with a maximum signal-to-noise ratio (SNR) of 32.7 dB at 25 kHz. The stability and sensitivity to temperatures up to 90 °C was also studied. Moreover, the proposed sensor offers the possibility to be applied as a wideband microphone or to be applied in more complex systems for structural analysis or imaging.
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    Application of a Fiber Optic Refractometric Sensor to Measure the Concentration of Paracetamol in Crystallization Experiments
    ( 2021) Liliana Patrícia Soares ; Cruz,P ; Susana Novais ; Ferreira,A ; Orlando Frazão ; Susana Oliveira Silva ; 4061 ; 4678 ; 7662 ; 7725
    A refractometric sensor was applied to measure in real-time the concentration of Active Pharmaceutical Ingredients (APIs) in crystallization experiments. Paracetamol was used as a model system due to the extensive literature available for this API. The refractometric sensor was fabricated by a simple and inexpensive method that consisted in splicing a short section of a multimode fiber to a single mode fiber. The compact geometry of this sensor, with an external diameter of just $125\ \mu\mathrm{m}$, allowed it to measure the concentration of paracetamol, both in a stirred tank crystallizer operating in batch and in an oscillatory flow crystallizer operating continuously. The proposed technique shows the potential to monitor the concentration of APIs in crystallizers of different sizes and geometries as an alternative to more expensive and complex analysis equipment.
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    Bi-core optical fiber for sensing o temperature, strain and torsion
    ( 2019) Lobo Ribeiro,ABL ; Susana Oliveira Silva ; Orlando Frazão ; José Luís Santos ; 4678 ; 347 ; 4061
    Bi-core optical fiber structures are studied for applications in sensing. In this paper, an analysis is performed on the spectral characteristics of light propagating in these fibers with central launching core illumination from a standard single mode fiber. Reflective and transmissive configurations are addressed. The characteristics of a reflective bi-core fiber structure for measurement of strain, temperature and absolute value of torsion are investigated and highlights for further research are presented.
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    Cavity length dependence on strain sensitivity for Fabry-Perot sensors
    ( 2022) António Vaz Rodrigues ; Reis,J ; Martins,AJM ; Catarina Silva Monteiro ; Susana Oliveira Silva ; Caridade,CMR ; Tavares,SO ; Orlando Frazão ; 4061 ; 4678 ; 6514 ; 6568
    This study presents the dependence of strain sensitivity on cavity length in conventional Fabry-Perot (F-P) sensors. A high number of F-P sensors were required and to ensure their reproducibility, a manufacturing process was developed to obtain similar sensors but with different types of lengths. A hollow-core silica tube was used to fabricate several F-P cavities by fusion splicing it between two sections of SMF28 fiber. The fabricated F-P has a varying length ranging from 15 to 2500 mu m. The cavities were measured under a microscope and the reflected spectrum was acquired for each one. Strain measurements were performed for a maximum strain of 1000 mu epsilon. The strain sensitivity showed a highly linear correlation with increment lambda(FSR). Small length variations for short cavities heavily affect the FSR value. The smallest and longest cavities present sensitivities of 8.71 and 2.68 pm/mu epsilon, respectively. Thermal characterization for low- and high-temperature regimes was also performed and is constant for tested sensors.
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    Curvature detection in a medical needle using a Fabry-Perot cavity as an intensity sensor
    ( 2020) Susana Novais ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 7725
    The use of optical sensors inside the needle can improve targeting precision and can bring real-time information about the location of the needle tip if necessary, since a needle bends through insertion into the tissue. Therefore, the precise location of the needle tip is so important in percutaneous treatments. In the current experiment, a fiber sensor based on a Fabry-Perot (FP) cavity is described to measure the needle curvature. The sensor is fabricated by producing an air bubble between two sections of multimode fiber. The needle with the sensor therein was attached at one end and deformed by the application of movements. The sensor presents a sensitivity of -0.152 dB/m-1 to the curvature measurements, with a resolution of 0.089 m-1. The sensory structure revealed to be stable, obtaining a cross-sensitivity to be 0.03 m-1/°C. © 2019 Elsevier Ltd
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    Curvature Sensor Based on a Long-Period Grating in a Fiber Ring Resonator Interrogated by an OTDR
    ( 2020) Magalhaes,R ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678
    The proposed technique demonstrates a fiber ring resonator interrogated by an optical time domain reflectometer (OTDR), for intensity sensing. By using this methodology, a cavity round trip time of 2.85 µs was obtained. For a proof of concept, a long-period grating was inserted in the resonant cavity operating as a curvature sensing device. A novel signal processing approach was outlined, regarding to the logarithmic behavior of the OTDR. Through analyzing the experimental results, an increase in the measured sensitivities was obtained by increasing applied bending. With curvatures performed from 1.8 m-1 to 4.5 m-1, the sensitivity values ranged from 2.94 dB·km-1 to 5.15 dB·km-1. In its turn, the sensitivities obtained presented a linear behavior when studied as a function of the applied curvature, following a slope of 0.86×10-3 dB. The advantages of applying this technique were also discussed, demonstrating two similar fiber rings multiplexed in a series of configurations. © 2019, The Author(s).
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    Detection of the Crystallization Process of Paracetamol with a Multi-Mode Optical Fiber in a Reflective Configuration
    ( 2020) Soares,L ; Susana Novais ; Ferreira,A ; Orlando Frazão ; Susana Oliveira Silva ; 4061 ; 4678 ; 7725
    A configuration of a refractometer sensor is described with the aim of optically detecting the crystallization process of paracetamol. The developed sensing head is based on a conventional cleaved multi-mode fiber. The fiber tip sensor structure was submitted to contact with the liquid of interest (paracetamol fully dissolved in 40% v/v of ethanol/water) and the crystallization process of paracetamol, induced with continued exposure to air, was monitored in real time.
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    Discrimination of benign and malignant lesions in canine mammary tissue samples using Raman spectroscopy: A pilot study
    ( 2020) Dantas,D ; Soares,L ; Susana Novais ; Vilarinho,R ; Moreira,JA ; Susana Oliveira Silva ; Orlando Frazão ; Oliveira,T ; Leal,N ; Faisca,P ; Reis,J ; 4061 ; 4678 ; 7725
    Breast cancer is a health problem that affects individual life quality and the family system. It is the most frequent type of cancer in women, but men are also affected. As an integrative approach, comparative oncology offers an opportunity to learn more about natural cancers in different species. Methods based on Raman spectroscopy have shown significant potential in the study of the human breast through the fingerprinting of biological tissue, which provides valuable information that can be used to identify, characterize and discriminate structures in breast tissue, in both healthy and carcinogenic environments. One of the most important applications of Raman spectroscopy in medical diagnosis is the characterization of microcalcifications, which are highly important diagnostic indicators of breast tissue diseases. Raman spectroscopy has been used to analyze the chemical composition of microcalcifications. These occur in benign and malignant lesions in the human breast, and Raman helps to discriminate microcalcifications as type I and type II according to their composition. This paper demonstrates the recent progress in understanding how this vibrational technique can discriminate through the fingerprint regions of lesions in unstained histology sections from canine mammary glands. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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    Environmental Sensitivity of Fabry-Perot Microcavities Induced by Layered Graphene-Dielectric Hybrid Coatings
    ( 2021) Peixoto,R ; Pires,JPS ; Catarina Silva Monteiro ; Raposo,M ; Ribeiro,PA ; Susana Oliveira Silva ; Orlando Frazão ; Lopes,JMVP ; 4061 ; 4678 ; 6568
    We propose a fiber-based environmental sensor that exploits the reflection-phase-shift tunability provided by the use of layered coatings composed of dielectric slabs spaced by conducting membranes. A transfer-matrix study is done in a simplified theoretical model, for which an enhanced sensitivity of the reflection interference pattern to the output medium is demonstrated, in the typical refractive index range of liquid media. An experimental configuration using a cascaded Fabry-Perot microcavity coated by a graphene oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its cost-effective chemical production method makes graphene oxide-based hybrid coatings excellent candidates for future real-life sensing devices.
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Femtosecond laser direct written off-axis fiber Bragg gratings for sensing applications
    ( 2020) Carlos Duarte Viveiros ; Vítor Oliveira Amorim ; João Miguel Maia ; Susana Oliveira Silva ; Orlando Frazão ; Pedro Jorge ; Fernandes,LA ; Paulo Vicente Marques ; 3565 ; 4061 ; 4287 ; 4678 ; 5872 ; 6407 ; 6596
    First order off-axis fiber Bragg gratings (FBGs) were fabricated in a standard single mode fiber (SMF-28e) through femtosecond laser direct writing. A minimum offset distance between the grating and core center of 2.5 µm was found to create a multimode section, which supports two separate fiber modes (LP0,1 and LP1,1), each split into two degenerate polarization modes. The resulting structure breaks the cylindrical symmetry of the fiber, introducing birefringence (˜10-4) resulting in a polarization dependent Bragg wavelength for each mode. Based on the modal and birefringence behavior, three off-axis FBGs were fabricated with 3.0, 4.5 and 6.0 µm offsets from the core center, and then characterized in strain, temperature, and curvature. The tested off-axis FBGs exhibited a similar strain sensitivity of ~1.14 pm/µ? and a temperature sensitivity of ~12 pm/C. The curvature and orientation angle were simultaneously monitored by analyzing the intensity fluctuation and the wavelength shift of the LP1,1 Bragg resonance. A maximum curvature sensitivity of 0.53 dB/m-1 was obtained for the off-axis FBG with a 3.0 µm offset. © 2020 Elsevier Ltd
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    Fiber Loop Mirror Based on Optical Fiber Circulator for Sensing Applications
    ( 2023) Paulo Robalinho ; Beatriz Gomes Soares ; Lobo,A ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 7405 ; 7700
    In this paper, a different Fiber Loop Mirror (FLM) configuration with two circulators is presented. This configuration is demonstrated and characterized for sensing applications. This new design concept was used for strain and torsion discrimination. For strain measurement, the interference fringe displacement has a sensitivity of (0.576 ± 0.009) pm?µe-1. When the FFT (Fast Fourier Transformer) is calculated and the frequency shift and signal amplitude are monitored, the sensitivities are (-2.1 ± 0.3) × 10-4 nm-1 µe-1 and (4.9 ± 0.3) × 10-7 µe-1, respectively. For the characterization in torsion, an FFT peaks variation of (-2.177 ± 0.002) × 10-12 nm-1/° and an amplitude variation of (1.02 ± 0.06) × 10-3/° are achieved. This configuration allows the use of a wide range of fiber lengths and with different refractive indices for controlling the free spectral range (FSR) and achieving refractive index differences, i.e., birefringence, higher than 10-2, which is essential for the development of high sensitivity physical parameter sensors, such as operating on the Vernier effect. Furthermore, this FLM configuration allows the system to be balanced, which is not possible with traditional FLMs.
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    High sensitivity strain sensor based on twin hollow microspheres
    ( 2019) Catarina Silva Monteiro ; Kobelke,J ; Schuster,K ; Bierlich,J ; Susana Oliveira Silva ; Orlando Frazão ; 4678 ; 6568 ; 4061
    A sensor based on 2 hollow core microspheres is proposed. Each microsphere was produced separately through fusion splicing and then joined. The resultant structure is a Fabry-Perot interferometer with multiple interferences that can be approximated to a 4-wave interferometer. Strain characterization was attained for a maximum of 1350 mu epsilon, achieving a linear response with a sensitivity of 3.39 /- 0.04 pm/mu epsilon. The fabrication technique, fast and with no chemical hazards, as opposed to other fabrication techniques, makes the proposed sensor a compelling solution for strain measurements in hash environments.
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    Optical Fiber Sensors for Structural Monitoring in Power Transformers
    ( 2021) Catarina Silva Monteiro ; Rodrigues,AV ; Viveiros,D ; Linhares,C ; Mendes,H ; Susana Oliveira Silva ; Paulo Vicente Marques ; Tavares,SMO ; Orlando Frazão ; 4061 ; 4287 ; 4678 ; 6568
    Power transformers are central elements of power transmission systems and their deterioration can lead to system failures, causing major disruptions in service. Catastrophic failures can occur, posing major environmental hazards due to fires, explosions, or oil spillage. Early fault detection can be accomplished or estimated using electrical sensors or a chemical analysis of oil or gas samples. Conventional methods are incapable of real-time measurements with a low electrical noise due to time-consuming analyses or susceptibility to electromagnetic interference. Optical fiber sensors, passive elements that are immune to electromagnetic noise, are capable of structural monitoring by being enclosed in power transformers. In this work, optical fiber sensors embedded in 3D printed structures are studied for vibration monitoring. The fiber sensor is encapsulated between two pressboard spacers, simulating the conditions inside the power transformer, and characterized for vibrations with frequencies between 10 and 800 Hz, with a constant acceleration of 10 m/s2. Thermal aging and electrical tests are also accomplished, aiming to study the oil compatibility of the 3D printed structure. The results reported in this work suggest that structural monitoring in power transformers can be achieved using optical fiber sensors, prospecting real-time monitoring.
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    Optical Fiber Temperature Sensors and Their Biomedical Applications
    ( 2020) Roriz,P ; Susana Oliveira Silva ; Orlando Frazão ; Susana Novais ; 4061 ; 4678 ; 7725
    The use of sensors in the real world is on the rise, providing information on medical diagnostics for healthcare and improving quality of life. Optical fiber sensors, as a result of their unique properties (small dimensions, capability of multiplexing, chemical inertness, and immunity to electromagnetic fields) have found wide applications, ranging from structural health monitoring to biomedical and point-of-care instrumentation. Furthermore, these sensors usually have good linearity, rapid response for real-time monitoring, and high sensitivity to external perturbations. Optical fiber sensors, thus, present several features that make them extremely attractive for a wide variety of applications, especially biomedical applications. This paper reviews achievements in the area of temperature optical fiber sensors, different configurations of the sensors reported over the last five years, and application of this technology in biomedical applications.
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    Ring Cavity Erbium-Doped Fiber for Refractive Index Measurements
    ( 2022) Perez-Herrera,RA ; Soares,L ; Susana Oliveira Silva ; Orlando Frazão ; 4678 ; 4061
    In this study, an interrogation system based on an erbium-doped fiber ring cavity for refractive index measurements is presented and experimentally demonstrated. This cavity ring includes a 1 × 3 coupler wherein one of the fiber output ports is used to increase the optical power of the system by means of an FBG used as a reflector. The other two output ports are used as a refractive index sensing head and reference port, respectively. An experimental demonstration of this proposed sensor system for the measurement of a distinct refractive index is presented.
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    A Self-Referencing Intensity-Based Fabry–Perot Cavity for Curvature Measurement
    ( 2019) Susana Novais ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 7725
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    Sputtering Deposition of TiO2 Thin Film Coatings for Fiber Optic Sensors
    ( 2022) Silva,D ; Catarina Silva Monteiro ; Susana Oliveira Silva ; Orlando Frazão ; Pinto,JV ; Raposo,M ; Ribeiro,PA ; Serio,S ; 4061 ; 4678 ; 6568
    Thin films of titanium dioxide (TiO2) and titanium (Ti) were deposited onto glass and optical fiber supports through DC magnetron sputtering, and their transmission was characterized with regard to their use in optical fiber-based sensors. Deposition parameters such as oxygen partial pressure, working pressure, and sputtering power were optimized to attain films with a high reflectance. The films deposited on glass supports were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regarding the deposition parameters, all three parameters were tested simultaneously, changing the working pressure, the sputtering power, and the oxygen percentage. It was possible to conclude that a lower working pressure and higher applied power lead to films with a higher reflectance. Through the analysis of the as-sputtered thin films using X-ray diffraction, the deposition of both Ti and TiO2 films was confirmed. To study the applicability of TiO2 and Ti in fiber sensing, several thin films were deposited in single mode fibers (SMFs) using the sputtering conditions that revealed the most promising results in the glass supports. The sputtered TiO2 and Ti thin films were used as mirrors to increase the visibility of a low-finesse Fabry–Perot cavity and the possible sensing applications were studied.
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    Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability
    ( 2021) Raposo,M ; Xavier,C ; Catarina Silva Monteiro ; Susana Oliveira Silva ; Orlando Frazão ; Zagalo,P ; Ribeiro,PA ; 4061 ; 4678 ; 6568
    Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device reliability, particularly in complex aqueous environments such as wastewater. In this work, the stability of GO layers in layer-by-layer (LbL) films of polyethyleneimine (PEI) and GO was investigated. The results led to the following conclusions: PEI/GO films grow linearly with the number of bilayers as long as the adsorption time is kept constant; the adsorption kinetics of a GO layer follow the behavior of the adsorption of polyelectrolytes; and the interaction associated with the growth of these films is of the ionic type since the desorption activation energy has a value of 119 ± 17 kJ/mol. Therefore, it is possible to conclude that PEI/GO films are suitable for application in optical fiber sensor devices; most importantly, an optical fiber-based interrogation setup can easily be adapted to investigate in situ desorption via a thermally stimulated process. In addition, it is possible to draw inferences about film stability in solution in a fast, reliable way when compared with the traditional ones.
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    Tuning of Fiber Optic Surface Reflectivity through Graphene Oxide-Based Layer-by-Layer Film Coatings
    ( 2020) Catarina Silva Monteiro ; Raposo,M ; Ribeiro,PA ; Susana Oliveira Silva ; Orlando Frazão ; 4061 ; 4678 ; 6568
    The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, by mounting combined bilayers of polyethylenimine (PEI) and GO layers using the Layer-by-Layer (LbL) technique. The reflectivity of optical fibers coated with graphene oxide layers is investigated for the telecom region allowing to both monitor layer growth kinetics and cavity characterization. Tunable reflective surfaces are successfully attained in both cleaved optical fibers and hollow microsphere fiber-based sensors by simply coating them with PEI/GO layers through the LbL film technique.