Search

This paper presents a novel probabilistic machine learning (PML) framework to estimate the Brillouin frequency shift (BFS) from both Brillouin gain and phase spectra of a vector Brillouin optical time-domain analysis (VBOTDA). The PML framework is used to predict the Brillouin frequency shift (BFS) along the fiber and to assess its predictive uncertainty. We compare the predictions obtained from the proposed PML model with a conventional curve fitting method and evaluate the BFS uncertainty and data processing time for both methods. The proposed method is demonstrated using two BOTDA systems: (i) a BOTDA system with a 10 km sensing fiber and (ii) a vector BOTDA with a 25 km sensing fiber. The PML framework provides a pathway to enhance the VBOTDA system performance.

The emergence of Industry 4.0 has brought new concepts to the factories that optimize and improve conventional processes. These technologies have brought assignments to the industrial robots that allow them to perform tasks faster and more precisely. The improvement of the robot’s proprioception capacity and tactile sensitivity using sensors is a useful approach to achieve those goals. Optical fibers are a viable technology to be used as sensors in robotic devices because they are electrically passive and present electromagnetic immunity. This paper proposes a Fiber Bragg Grating (FBG) based sensing system to monitor robotic manipulators during their operation. It corresponds to smart textiles installed on the robot’s body to detect interactions with the environment. A mathematical model is proposed to find what should be the greatest distance between adjacent FBGs to detect contact at any point between them. From this, it is possible to obtain a minimum number of sensors to detect contact at any point and guarantee the highest spatial resolution of the system with lower costs. The tactile system is formed of a group of optical fibers with multiplexed FBGs embedded in silicone rubber. The optical fibers with the sensors are positioned between layers of polyethylene foam and cotton fabric. After the manufacturing process, temperature and force characterization were done on the sensors which make up the smart textiles. In the characterization results, almost all the FBG presented values of R² on the linear regression superior to 0.94. Individual analysis is performed for the sensors which present a low coefficient of determination. Finally, the system was tested in an experimental validation in which the robot was hit while executing a task. From the results, it can be observed that the system can provide the position on the robot’s body, the amplitude in terms of force and the instant of time in which an external impact occurred. published

In this paper, an on-chip optical circulator on the InP-membrane-on-Si (IMOS) platform is demonstrated. The circulator is composed of two multi-mode interferometers (MMIs), four polarization converters (PCs), and a Cerium-doped Yttrium Iron Garnet (Ce:YIG) die. The Ce:YIG die is adhesively bonded on the InP membrane via a 125-nm thin bonding layer. Nonreciprocal phase shift (NRPS) is employed in the presence of a transverse magnetic field. The device works as a 4-port optical circulator with a maximum optical isolation of 27.0 dB and a minimum optical isolation of 18.6 dB for the TE mode. The measured optical isolation bandwidth is 0.12 nm. Two methods are proposed in order to improve the optical isolation bandwidth.

This paper presents a novel cable-driven exoskeleton (BiEXO) for the upper limb including shoulder and elbow joints. BiEXO is made of carbon fiber that is inspired by the Bamboo structure. The key components of BiEXO are carbon fiber tubes that mimic bamboo tubes. A combined driver is developed for BiEXO with two cable-driven mechanisms (CDMs) and a power transmission belt (PTB). The CDMs are used for shoulder and elbow flexion/extension movement utilizing cables to mimic the skeletal muscles function, while the PTB system drives a shoulder link to mimic the scapula joint for shoulder abduction/adduction movement. Simulation studies and evaluation experiments were performed to demonstrate the efficacy of the overall system. To determine the strength-to-weight of the bamboo-inspired links and guarantee high buckling strength in the face of loads imposed from the user side to the structure, finite element analysis (FEA) was performed. The results show that the carbon fiber link inspired by bamboo has more strength in comparison to the common long carbon fiber tube. The kinematic configuration was modeled by the modified Denavit-Hartenberg (D-H) notation. The mean absolute error (MAE) was 5.9 mm, and the root-mean-square error (RMSE) was 6 mm. In addition, verification experiments by tracking the trajectory in Cartesian space and the wear trials on a subject were carried out on the BiEXO prototype. The satisfactory results indicate BiEXO to be a promising system for rehabilitation or assistance in the future.

Dissertação de mestrado em Técnicas de Caracterização e Análise Química, A corrosão das armaduras é uma das principais causas de deterioração das estruturas de betão, resultando em elevados custos de reparação, manutenção e reabilitação. A carbonatação e a presença de agentes agressivos, como os iões cloreto, estão na origem desse processo. Nas últimas décadas, o uso de sensores de fibra ótica (SFO) para monitorar os parâmetros físicos de estruturas na área da engenharia civil tem sido amplamente utilizado. A monitorização de estruturas de betão com recurso aos SFO funcionalizados com materiais sol-gel revelou-se uma abordagem interessante para aumentar a sua vida útil. O método sol-gel é versátil, ecológico e um processo simples que permite sintetizar novos materiais híbridos orgânico-inorgânico (HOI) com propriedades únicas, incluindo a estabilidade química, propriedades dielétricas adequadas como resistência térmica e fotoquímica. Além disso, este método permite controlar diversos parâmetros experimentais como o tipo de precursores, a porosidade da matriz, o tempo e a temperatura de cura dos materiais HOI. O presente trabalho relata a síntese de matrizes de materiais HOI, obtidos a partir de um siloxano funcionalizado, 3-glicidoxipropiltrimetoxissilano, por reação com um oligopolímero denominado Jeffamine THF-170® para potencial aplicação em SFO para monitorizar parâmetros cruciais nas estruturas de betão. As matrizes HOI foram dopadas com diferentes teores de zeólitos AgY e NaY de modo a permitirem a deteção as espécies agressivas no betão. A caraterização dos materiais sintetizados permitiu evidenciar caraterísticas morfológicas, químicas, térmicas e elétricas adequadas à sua incorporação em SFO., Corrosion of reinforcement is one of the major causes of deterioration of concrete structures resulting in high repair, maintenance, and rehabilitation costs. Carbonation and the presence of aggressive agents, such as chloride ions, are at the main source of this process. In the last few decades, the use of optical fiber sensors (OFS) to monitor the physical parameters of structures in the civil engineering field has been widely employed. The monitoring of concrete structures using functionalized OFS with sol-gel films revealed to be an interesting approach to increase its service life. The sol-gel method is versatile, environmentally friendly and a simple process that allows to synthesize new organic-inorganic hybrid (OIH) materials with unique properties including chemical stability, suitable dielectric properties as thermal and photochemical resistance. Moreover, this method can control several experimental parameters such as precursors, matrix porosity, curing time and temperature of the OIHs to be produced. This work reports the synthesis of OIH matrices, which were obtained using a functionalized siloxane, 3- glycidoxypropyltrimethoxysilane, by reaction with an oligopolymer named Jeffamine® THF-170 for potential application on an OFS for health monitoring of concrete structures. The OIH matrices were doped with different contents of AgY or NaY zeolites to detect the aggressive species in the concrete. The characterization of the synthesized HOI materials revealed morphological, chemical, thermal, and electrical properties suitable for their incorporation into SFO., Agradeço a oportunidade de participação e o suporte dado no âmbito do Projeto SolSensors: Desenvolvimento de sensores de fibra ótica avançados para monitorização da durabilidade de estruturas de betão, com referência POCI-01-0145-FEDER031220 suportado pelo programa COMPETE 2020 – Programa Operacional Competitividade e Internacionalização, Programa Operacional Regional de Lisboa na sua componente FEDER e à FCT – Fundação para a Ciência e Tecnologia, I.P. (UID/QUI/00686/2016).

We demonstrate of an off-centered tilted fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) fiber as a curvature sensor. The gratings were inscribed using a femtosecond (fs) laser with the direct write, plane-by-plane method due to its high flexibility and suitability for customization, particularly for the development of a single-peak spectrum in multimode CYTOP fiber. The grating is applied to curvature sensing, where the spectral features, namely the wavelength shift and reflected optical power, are analyzed with respect to the curvature angle on the optical fiber. The off-center and tilted FBG response as a function of the angle is compared with a centered and uniform FBG inscribed in CYTOP fiber using the same inscription method and laser parameters. Results show a significant improvement for the off-center grating when the wavelength shift information is considered and lower optical power sensitivity as a function of the angle with respect to the centered FBG. In addition, the temperature sensitivity differences of the two gratings, enables the development of temperature-insensitive angle sensor using a single off-center tilted FBG.

This paper describes a Fabry–Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under real industrial conditions, and enables temperature-compensated online measurement of emulsion concentration with a high resolution of 0.03 Brix. The measuring system was equipped with filtering of the emulsion and automatic cleaning of the sensor, which proved to be essential for successful implementation of a fiber optic RI sensor in machining emulsion monitoring applications.

Brillouin optical correlation-domain reflectometry (BOCDR) is known as one of the distributed fiber-optic strain/temperature sensing techniques. Recently, a high-speed BOCDR configuration with no measurable strain limit has been developed, but only a sampling rate of 50 Hz has been experimentally demonstrated, limited by the use of a commercial microwave frequency sweeper (MFS). In this work, by replacing the MFS with an independent voltage-controlled oscillator driven by a function generator, we experimentally show via vibration detection that this system can achieve a sampling rate of up to 20 kHz. We newly observe the systematic noise peculiar to such high-speed operation, which is found to originate from the unintended intensity modulation of the laser output. We also demonstrate the suppression of this noise by band-elimination filtering.

In this work a new multiparameter sensor platform based on lossy mode resonances is presented. The structure consists of a soda-lime optical slab waveguide butt-coupled to multimode optical fibers. A variable thickness thin-film is deposited to generate multiple independent resonances on the same waveguide, which can be monitored using a single spectrometer. In order to show the potentiality of the structure, a broad resonance was selectively narrowed by etching sections of the LMR producer thin film. The spectral width is progressively reduced, allowing to selectively isolate independent resonances, which opens the path for multiple LMR generation in the same spectra in a multiparameter sensing platform. The experimental results were corroborated with a theoretical analysis based on the finite difference method (FDM). As a proof of concept, two refractometers on the same waveguide were fabricated and tested using PDMS cells. This platform can be easily miniaturized in order to integrate multiple sensors at low cost, what can be of interest for the development of multi-analyte biosensors probes. IEEE This work was supported in part by the Spanish Ministry of Economy and Competitiveness under Grant PID2019-106070RB-I00 and Grant PID2019-106231RB-I00.

The power coupling between two light diffusing multimodal optical fibers of equal and finite lengths that are parallel oriented, and which are coupled through scattering processes, is investigated both theoretically and experimentally. In particular, a simple analytical model of the inherent coupling coefficient, derived according to a perturbation approach in a weak-coupling regime, is developed. The modelling results have been compared with the measurements performed, as a function of fiber distance and coupling length at three different wavelengths, and a close agreement is proved. The obtained results provide better understanding of the power coupling mechanism and of the inherent functional dependence on the main structural parameters of the two-fiber configuration.

An ultra-short fiber Bragg grating with a grating length of 0.2 mm and constant grating period (uniform FBG) is proposed as an integrated dispersive element for spectral analysis in a single-mode glass fiber. This dispersive element is used to set up a fiber optical spectrometer that demonstrated an average spectral resolving power of 825, a pixel resolution of 0.02 nm/pixel, and a 40 nm bandwidth covering the 810-850 nm wavelength range. Furthermore, the dependence of this dispersive element on light polarization was examined, which induces a reduction in the wavelength accuracy up to ±0.05 nm. Finally, the investigated spectrometer to function well as a part of a readout device for fiber Bragg grating sensors is presented. Short uniform Bragg gratings as dispersive elements allow the manufacturing of miniaturized, compact spectrometers without additional focusing components between the FBG and detector.

Funding Information: This work was supported by AI spider silk threading (ASSET) in the AIPSE program of the Academy of Finland under Project 317018. Publisher Copyright: Crown Gel-like matter is used extensively in a wide range of application fields including industrial applications such as the manufactory and assembly of garment and footwear products, soft macro/micro-robotics, medical diagnostics, and drug delivery. However, the manipulation of gel-like matter is very challenging, due to its high deformability, high viscosity, and fast phase changing. In this letter, we propose a novel biomimetic robotic fiber threading approach based on impedance control with force tracking. The highly integrated approach can control the impedance of the fiber during both threading and solidification of the fiber and characterize the mechanical properties of the fabricated fibers in the very same setup without changing parts. The impedance control method has also been adapted in this letter by adding a real-time estimator for continuously estimating the stiffness of the threading force for highly accurate control. The resulted fibers using the proposed approach demonstrates higher performances in all terms of toughness, stiffness, elongation and strength, compared to the traditional velocity controlled fiber fabrication approach.

Distributed optical fiber sensors (DOFSs) have faced the challenge of measuring transverse stress along the fiber and the current main approach has been based on polarization coupling effect in polarization-maintaining fibers (PMFs), which has short sensing length and high dependence on direction of exerted stress. Instead, here we propose a novel distributed transverse stress sensor (DTSS) based on coupling effect between linearly-polarized (LP) modes in weakly-coupled few-mode-fibers (FMFs). In this scheme, multiple LP modes could be considered as independent spatial channels without stress perturbation because of ultralow inherent modal crosstalk, while quantifiable and spatially-resolvable mode coupling for a probe signal will occur under transverse stress satisfying phase-matching conditions. A proof-of-concept DTSS system is verified based on weakly-coupled two-mode fibers and mode-selective couplers for mode conversion. Moreover, we show that the scheme is little affected by mild common parameters including temperature, strain, twist, direction of stress, or state-of-polarization (SOP), which is crucial for accurate stress analysis under complex environmental conditions. The proposed DTSS scheme has simple structure, high flexibility for different sensing ranges and resolutions, and high collaborating capability with other sensing mechanisms.

To overcome the poor low-frequency response sensitivity of differential phase detecting interferometer, an improved differential phase detecting optical fiber interferometer with a time domain low frequency compensation scheme is designed and implemented, effectively compensating the low frequency loss of the system by means of recursive accumulation method. Theoretical derivation and experimental verification are conducted in this paper. The experimental results indicate that the improved system can significantly enhance the amplitude of 10 Hz signal and signals with high fidelity can be obtained because the compensated system responds equally both to the high and low frequency signals. Further experiments in the buried pipelines monitoring reveal that the signal-to-noise ratio is obviously improved by 22 dB approximately compared with the traditional system. The positioning error of the proposed system is within ±20 m along a 40 km sensing fiber. The differential phase detection interferometer compensated by the proposed scheme has potential application in low-frequency fields such as seismic wave detection, hydrophones, sonar, pipeline monitor and geological detection.

High temperature detection is a constant challenge for condition monitoring under harsh environments in optical fiber sensors research. In this study, the temperature response characteristics of guided acoustic wave Brillouin scattering (GAWBS) spectra in silica single-mode fiber (SMF) up to 800 °C are experimentally investigated, demonstrating the feasibility of the method for high-temperature monitoring. With increasing temperature, the resonance frequency of GAWBS spectra increases in a nearly linear manner, with linearly fitted temperature-dependent frequency shift coefficients of 8.19 kHz/°C for TR2,7 mode and 16.74 kHz/°C for R0,4 mode. More importantly, the linewidth of the GAWBS spectra is observed to narrow down with increasing temperature with a linearly fitted rate of −6.91 × 10−4/°C for TR2,7 modes and −8.56 × 10−4/°C for R0,4 modes. The signal-to-noise ratio of the GAWBS spectra induced by both modes increase by more than 3 dB when the temperature rises from 22 °C to 800 °C, which indicates that the proposed sensing scheme has better performance in high-temperature environments, and are particularly suitable for sensing applications in extreme environments. This study confirms the potential of high-temperature sensing using only GAWBS in silica fibers without any complex micromachining process, which has the advantages of strong mechanical strength, simple structure, easy operation, and low cost.

This paper presents the development and application of a multiplexed intensity variation-based sensor system for multiplane shape reconstruction. The sensor is based on a polymer optical fiber (POF) with sequential lateral sections coupled with a flexible light-emitting diode (LED) belt. The optical source modulation enables the development of 30 independent sensors using one photodetector, where the sensor system is embedded in polydimethylsiloxane (PDMS) resin in two configurations. Configuration 1 is a continuous PDMS layer applied in the interface between the flexible LED belt and the POF, whereas Configuration 2 comprises a 20 mm length PDMS layer only on each lateral section and LED region. The finite element method (FEM) is employed for the strain distribution evaluation in different conditions, including the strain distribution on the sensor system subjected to momentums in roll, pitch and yaw conditions. The experimental results of pressure application at 30 regions for each configuration indicated a higher sensitivity of Configuration 1 (83.58 a.u./kPa) when compared with Configuration 2 (40.06 a.u./kPa). However, Configuration 2 presented the smallest cross-sensitivity between sequential sensors (0.94 a.u./kPa against 45.5 a.u./kPa of Configuration 1). Then, the possibility of real-time loading condition monitoring and shape reconstruction is evaluated using Configuration 1 subjected to momentums in roll, pitch and yaw, as well as mechanical waves applied on the sensor structure. The strain distribution on the sensor presented the same pattern as the one obtained in the simulations, and the real-time response of each sensor was obtained for each case. In addition, the possibility of real-time loading condition estimation is analyzed using the k-means algorithm (an unsupervised machine learning approach) for the clusterization of data regarding the loading condition. The comparison between the predicted results and the real ones shows a 90.55% success rate. Thus, the proposed sensor device is a feasible alternative for integrated sensing in movement analysis, structural health monitoring submitted to dynamic loading and robotics for the assessment of the robot structure.

The employability of photonics technology in the modern era’s highly demanding and sophisticated domain of aerospace and submarines has been an appealing challenge for the scientific communities. In this paper, we review our main results achieved so far on the use of optical fiber sensors for safety and security in innovative aerospace and submarine applications. In particular, recent results of in-field applications of optical fiber sensors in aircraft monitoring, from a weight and balance analysis to vehicle Structural Health Monitoring (SHM) and Landing Gear (LG) monitoring, are presented and discussed. Moreover, underwater fiber-optic hydrophones are presented from the design to marine application.

Refereed/Peer-reviewed A novel optical fiber sensor using exposed-core fiber (ECF) to excite whispering gallery modes (WGMs) within a high refractive index barium titanate glass microsphere is proposed for achieving label-free real-time specific DNA detection. The microsphere is encapsulated into the exposed channel of the ECF allowing for physical stability while excited WGMs via the evanescent field. The structure enables the sensing area to be exposed to a large amount of aqueous solution and better contact with the sample to be analyzed. Using a transmission measurement, a high Q-factor in the order of 104 is obtained in an aqueous environment. To the best of our knowledge, this is the best Q-factor level obtained by the in fiber WGM sensor in an aqueous environment. Specific sequences of probe DNA are then bound to the surface of the microsphere so that specific detection of complementary DNA can be realized by tracking the wavelength shift the WGM resonance. Experimental results show a red shift of 5.6 pm for complementary DNA hybridization detection and less than 1 pm fluctuation for non-complementary DNA detection. The portable integrated sensor with miniature size has great potential for aqueous environmental sensing applications in the fields of diseases diagnostics, chemical analysis, and environmental protection.

Our group, involving researchers from different universities in Campania, Italy, has been working for the last twenty years in the field of photonic sensors for safety and security in healthcare, industrial and environment applications. This is the first in a series of three companion papers. In this paper, we introduce the main concepts of the technologies employed for the realization of our photonic sensors. Then, we review our main results concerning the innovative applications for infrastructural and transportation monitoring.

One of the key elements for early diagnosis of acute and severe diseases is the development of ultra-sensitive detection methods, which are required to analyze the pathological state of the human body from trace amounts of substances in blood or urine. Surface plasmon resonance (SPR) optical fiber biosensors, particularly those based on tilted fiber Bragg gratings (TFBG), have emerged in recent years as a novel solution for in-situ biomedical detection. TFBGs can sensitively detect the physical and chemical interactions between biomolecules in real-time by sensing minute changes in refractive index, even in vivo. The TFBG-based SPR method can achieve rapid and accurate analysis of biological samples by demodulating the wavelength, intensity, phase and polarization state of the optical spectrum. In addition, TFBG-based SPR fiber optic sensors are capable of simultaneously detecting the absolute or relative values of multiple parameters. This effectively eliminates the interference from the ambient environment and ensures the stability and reliability of the sensor.

[EN]In general, a sensor is used to monitor a single parameter only, and in many cases, a reference sensor is necessary to compensate the effect of temperature. Here, we demonstrate that a single supermode interferometer is capable of monitoring two parameters simultaneously. Said interferometer was fabricated with a segment of strongly coupled multicore fiber fusion spliced at the end of a standard single mode fiber. The free end of the multicore fiber was flat, thus, it behaved as a low reflectivity mirror whose reflection depended on the external refractive index. The reflection spectrum of our supermode interferometer consisted of well-defined periodic maxima and minima whose values and position varied when the interferometer was exposed to refractive index and temperature changes. In the Fourier domain, the changes of the interference pattern can be decoded easily. We demonstrate that the supermode interferometer here proposed can be useful to measure the thermo-optic coefficient of a sample. An important advantage of the device reported here is that the length of the multicore fiber is not determinant on the performance of the sensor. In addition, the device can be reused multiple times. This work was supported in part by the Ministerio de Economia y Competitividad (Spain) and the European Regional Development Fund under Grants PGC2018-101997-B-I00 and RTI2018-094669-B-C31, and in part by the Departamento de Educacion del GobiernoVasco, underGrant IT933-16.

In this work, a multi-parameter point sensor based on the combination of Fabry-Perot (FP) and the anti-resonant (AR) reflecting guidance in cascade configuration is proposed and experimentally demonstrated. This structure, based on FP interference and AR reflecting guidance, was fabricated with two different air micro-cavities. The attained experimental results showed different strain and temperature sensitivities for the antiresonance contribution. However, when analyzing the FP interference, only strain sensitivity was observed, demonstrating that this air micro-cavity was also insensitive to temperature variations. This work was supported by the Spanish AEI projects TEC2016-76021-C2 and PID2019-107270RB-C22, FEDER Funds, the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 838143, Projects for young researches UPNA 2019, “Caja Navarra” and “la Caixa” foundations under agreement LCF/PR/PR13/51080004 and the grant BGP18/00180 of the “Beatriz Galindo” programme from the Spanish Ministry of Science, Innovation and Universities.

The development of novel textile materials capable of controlled interaction with the environment has contributed to the growth of smart textiles. Nevertheless, the ubiquitous integration of plastic and electronic components into textile structures will bring new challenges regarding the use of material resources and waste management. Focusing on this problem, the present work explores the use of carboxymethyl cellulose (CMC)-based optical waveguides to create textile-based optical sensors. Following an interdisciplinary approach, the research was conducted by combining methods from textile design, material science, and photonics. CMC optical fiber and planar waveguide were compared in corresponding textile structures. We present the laboratory testing results of initial proof of concept samples of bio-based woven smart textiles demonstrating their touch, bending.. and water optical sensing capabilities.

Society’s dependency on fossil fuels is becoming a critical obstacle regarding environmental sustainability. The concentrated political power on institutions related to the fossil fuel market represents a worldwide energy dependence. Alternative energy sources could be explored to supply the energetic needs of human activity and better distribute the energy supply around the world. However, to be able to make use of these alternative energies is mandatory to consume them right away or to store them as potential energy, otherwise, they would be wasted. Multiple initiatives are investing and aiming to reduce the usage of fossil fuels by stimulating the research and development of alternative energy sources, together with energy storage development is crucial to potentialize the utilization and adoption of such alternative energies. Nowadays, rechargeable Li-ion batteries are the most adopted, scalable, and demanded energy storage devices in the world. The scarcity of information regarding the interior of the LiBs currently hinders the improvement of the accuracy and predicting capabilities of current battery management algorithms and models, while equally limiting attempts to refine the battery thermal design due to the absence of heat-transfer information. This has led to increasing interest in spatiotemporal imaging of the thermal flows within a cell using temperature sensors. The tracking of gas production and/or pressure variations are also very recent topics of sensing inside the LIBs. However, due to the difficulty and complexity of sensing, the integration of the sensors inside the battery cells being necessary, they were not yet so explored. In this work, hybrid optical fiber sensors based on Fabry-Perot Interferometers (FPIs) and Fiber Bragg Grating (FBG) sensors were successfully developed and characterized to discriminate two impactful parameters (pressure and temperature) internally and externally simultaneously on cylindrical lithium-ion batteries (LiB) in order to improve their operation in safety conditions. The proposed hybrid sensors consist of a photosensitive single-mode fiber (SMF), where the FBGs were inscribed and spliced to a small section of a hollow-core fiber (HCF). To create the FPI, the HCF’s tip was submerged in a UV-photosensitive polymer, creating three cavities and two observable light beam interferences in the optical spectrum, resulting in two Fabry-Perot responses. Out of four created sensors with different HCF and liquid polymer cavity’s lengths, three of them were calibrated to temperature and pressure. By tracking the FP fringes and the resulting envelope shifts of the spectral responses, it achieved higher sensitivities for the hybrid sensor with 175.86 μm and 26.38 μm of cavities’ lengths for the envelope analysis, with 31.65 nm/bar and 1.53 nm/°C, with the pressure sensitivity being the highest recorded value for this type of configuration. After calibrating steps, the hybrid sensor D was selected and embedded inside a commercial LG 18650 LiB to internally dual-parameter sensing. The placement of the FBGs and the Fabry-Perot cavity allow the detection of pressure in all battery and temperature changes near the negative and positive terminals, and in the middle of the battery during several galvanostatic cycles. Externally, were also placed one optical fiber with four FBGs to acquire external temperature variations in the outer case, being one of them outside of the case to ambient temperature control. Galvanostatic cyclic tests were performed through different temperatures, 25.0 and 40.0 °C. The online detection of the FP fringes and FBGs peaks allows, through a matrixial method discrimination, obtain the temperature and pressure variations. It resulted in successful temperature and pressure readings, resembling some occurrences presented in the available literature and other findings which concerns to pressure and temperature behaviours in different battery locations can be highlighted, like some of the thermal events were undetected by the external FBG sensors. Although some key factors need to be further studied to understand the potential of this sensor, like the long-term stability, however this hybrid sensor design has enormous potential to perform simultaneous measurements of internal pressure and temperature shifts during normal and abnormal working conditions of an 18650 LiB. A dependência da sociedade em combustíveis fósseis está a tornar-se num grande obstáculo no que toca à sustentabilidade ambiental. O poder político concentrado nas instituições relacionadas com o mercado de combustíveis fósseis representa uma dependência energética global. Fontes de energia alternativas podem ser exploradas para fornecer toda a energia da atividade humana e distribuí-la melhor pelo mundo. Todavia, para se utilizar estas energias alternativas, é necessário consumi-las imediatamente ou armazená-las como energia potencial, senão serão desperdiçadas. Múltiplas áreas estão a investir para procurar reduzir o uso de combustíveis fósseis ao estimular a investigação e o desenvolvimento de fontes de energia alternativas que, juntamente com o desenvolvimento de formas de armazenar energia, é crucial para potencializar a utilização e adoção de tais energias. Atualmente, baterias de iões de Lítio (LiBs) são as mais utilizadas, escaladas e pedidas fontes de armazenamento de energia pelo mundo. A falta de informação sobre o interior das baterias atualmente dificulta o aumento da precisão e capacidade de previsão dos atuais algoritmos e modelos dos sistemas de gestão das baterias (BMS), enquanto limita as tentativas para refinar o design térmico das baterias devido à ausência de informação sobre as transferências de calor. Isto levou ao aumento do interesse nas imagens tempo-espaciais dos fluxos térmicos dentro de uma bateria através de sensores de temperatura. O acompanhamento da variação de produção de gases e/ou de pressão são também tópicos recentes em sensores dentro de LiBs. No entanto, devido à dificuldade e complexidade de deteção, a integração dos sensores dentro de baterias, sendo necessárias, não estão a ser exploradas. Neste trabalho, sensores de fibra ótica híbridos baseados em Interferómetros Fabry-Perot (FPIs) e em redes de Bragg (FBGs) foram desenvolvidos e caraterizados com sucesso para discriminar simultaneamente dois fatores impactantes, pressão e temperatura, em LiBs cilíndricas para melhorar a sua operação em condições de segurança. O sensor híbrido proposto consiste numa fibra monomodo (SMF), onde foram gravadas FBGs, fundida com um curto segmento de tubo oco cilíndrico (HCF). Para criar o FPI, a ponta da HCF foi mergulhada num polímero líquido, fotossensível (PS) a radiação ultravioleta (UV), criando três cavidades e duas interferências visíveis no espetro ótico, resultando em duas respostas Fabry-Perot. Dos quatro sensores fabricados com diferentes comprimentos de HCF, três deles foram calibrados à temperatura e à pressão. Ao seguir a variação das franjas das respostas Fabry-Perot e dos envelopes resultantes, atingiu-se maiores sensibilidades para o sensor híbrido com 175.86 μm e 26.38 μm de comprimento das cavidades através da análise dos envelopes com 31.65 nm/bar e 1.53 nm/°C, sendo a sensibilidade à pressão o maior valor registado para sensores nesta configuração. Após a calibração, o sensor híbrido D foi selecionado e colocado dentro de uma LiB comercial LG 18650 para medir internamente os dois parâmetros. O posicionamento das FBGs e da cavidade Fabry-Perot permitem a deteção de variações de pressão no terminal positivo da bateria, e de temperatura perto dos terminais negativos e positivos, e no meio da mesma, durante os testes cíclicos galvanostáticos. Externamente, foi acrescentada uma fibra ótica com quatro FBGs para adquirir as variações de temperatura externas na cápsula protetora da bateria, sendo uma delas destinadas ao controlo da temperatura ambiente. Os testes galvanostáticos foram realizados a diferentes temperaturas, 25.0 °C e a 40.0 °C. A deteção em tempo real das franjas Fabry-Perot e dos picos das FBGs permitiu, através de um método de discriminação matricial, obter as variações de temperatura e pressão. Resultou em leituras bem-sucedidas de temperatura e pressão, apresentando comportamentos similares a descritos pela literatura e vários comportamentos referentes aos sinais de temperatura e pressão foram identificados, tal como alguns eventos térmicos que foram detetados pelas FBGs externas. Apesar de alguns fatores importantes ainda precisarem de algum aprofundamento para se avaliar o potencial deste sensor híbrido, como a estabilidade a longo termo, este sensor tem um enorme potencial para realizar medições simultâneas das variações de pressão e temperatura nas 18650 LiBs, durante os seus períodos de normal e anormal funcionamento. Mestrado em Engenharia Física

In this paper, a ratiometric approach to sensing temperature variations is shown using specialty fiber optic devices. We analyzed the transmission response of cascaded segments of multicore fibers (MCFs), and dissimilar lengths were found to generate an adequate scheme for ratiometric operation. The perturbation of optical parameters in the MCFs translates to a rich spectral behavior in which some peaks increase their intensity while others decrease their intensity. Thus, by selecting opposite-behavior peaks, highly sensitive ratiometric measurements that provide robustness against spurious fluctuations can be performed. We implemented this approach using seven-core fiber (SCF) segments of 5.8 cm and 9.9 cm. To test the system’s response under controlled perturbations, we heated one of the segments from ambient temperature up to 150 °C. We observed defined peaks with opposite behavior as a function of temperature. Two pairs of peaks within the interrogation window were selected to perform ratiometric calculations. Ratiometric measurements exhibited sensitivities 6–14 times higher than single-wavelength measurements. A similar trend with enhanced sensitivity in both peak pairs was obtained. In contrast to conventional interferometric schemes, the proposed approach does not require expensive facilities or micrometric-resolution equipment. Moreover, our approach has the potential to be realized using commercial splicers, detectors, and filters.

In this work, the development of several hybrid optical fiber sensors based on hollow core fibers was aimed. The sensing structures enhanced multiple interferometers in a single sensing cavity, which were monitored towards simultaneous measurement of multiple parameters. Firstly, a study was carried out over the different interferometers that arise in a section of silica capillary tube (SCT) spliced between two single mode fibers (SMF). The Fabry-Perot interferometer (FPI), antiresonant guidance (AR) and the Mach-Zehnder interferometer (MZI) were explored. The first hybrid sensor fabricated was based on the SMF-SCT-SMF structure with access channels instilled on the fiber with two methods that allowed the fabrication of an up to two-access channel sensor. The sensor was characterized to pressure and temperature in a reflection scheme, enhancing an FPI and AR for a 2 mm sensor. Different sensitivities were attained for both interferometers, thus the simultaneous measurement of the parameters under study was proposed. A different explored configuration was the balloon-like fiber sensor with the SMF-SCT-SMF configuration. This structure was bent in a balloon shape with the SCT in the top-center position. The 1.2 cm SCT length sensor was studied in a transmission configuration with a 4 cm balloon-length, enhancing AR guidance as well as an MZI, which was enforced by the bending derived from the balloon structure. Simultaneous measurement of displacement and temperature was achieved for the MZI and AR. Additionally, an access channel was instilled in the SCT, and the balloon-like sensor was sensitive to pressure for both components. Finally, a configuration based on a SMF-hollow square core fiber-SCT was developed and studied in a reflection scheme. A 439 μm long hollow square core fiber was able to excite three distinct FP cavities in a single sensing element. The different modes were monitored towards several physical parameters by using the Fourier band-pass filter method. The sensor was able to achieve a multiparameter simultaneous measurement of pressure, temperature, and curvature, for a certain fixed rotation. All the studied inline sensors all revealed potential hybrid application for simultaneous measurement of several parameters while constituting a single sensing head. The sensors possess reduced dimensions, high robustness, and simple configurations, making them great contenders for their implementation on several applications. Neste trabalho foram desenvolvidos vários sensores híbridos em fibra ótica baseados em fibras de núcleo oco. Num só elemento sensor foram excitados vários interferómetros que foram monitorizados para a medição simultânea de múltiplos parâmetros. Primeiramente, um estudo foi desenvolvido sobre os interferómetros excitados numa secção de tubo de sílica fundida entre duas fibras monomodo. Foram explorados os interferómetros de Fabry-Perot (FP), propagação por antirressonância (AR), e de Mach-Zehnder (MZ). O primeiro sensor híbrido desenvolvido foi baseado na fusão de um tubo capilar de sílica entre duas fibras monomodo onde se adicionaram canais de acesso através de dois métodos diferentes, tendo sido possível obter sensores com até dois canais de acesso. Foi feita a caracterização à pressão e temperatura de vários sensores com diferentes comprimentos onde se observam simultaneamente FP e AR. Foi feita uma proposta para medição simultânea dos dois parâmetros devido às diferentes sensibilidades dos interferómetros. Uma outra configuração foi explorada onde o sensor foi curvado num formato balão, com o tubo capilar na posição superior central do mesmo balão. Num esquema em transmissão, um sensor com 1.2 cm num balão com 4 cm de comprimento apresentou AR e excitou um interferómetro de MZ forçado pela curvatura induzida pelo balão. A medição simultânea de deformação e temperatura foi obtida para a AR e MZ. Adicionalmente, foi criado um canal de acesso no capilar que permitiu deteção de pressão para ambos os interferómetros. O último sensor desenvolvido foi baseado numa fibra de núcleo quadrado oco fundida entre uma fibra monomodo e um tubo capilar de sílica. Em reflexão, um sensor com 439 μm permitiu a excitação de três cavidades de FP distintas num só elemento sensor. Os vários modos foram monitorizados a vários parâmetros físicos através do método de filtros passa-banda de Fourier. O sensor foi proposto para medição simultânea de pressão, temperatura e curvatura, para uma certa rotação fixa. Os dispositivos fabricados contendo apenas um elemento sensor revelaram possíveis aplicações como sensores híbridos para medição simultânea de vários parâmetros. Os sensores possuem tamanho reduzido e alta robustez, juntamente com configurações simples, tornando-os excelentes candidatos para a sua implementação em várias aplicações. Mestrado em Engenharia Física

In this work, optical fiber sensors were developed and optimized for biomedical applications in wearable and non-intrusive and/or invisible solutions. As it was intended that the developed devices would not interfere with the user's movements and their daily life, the fibre optic sensors presented several advantages when compared to conventional electronic sensors, among others, the following stand out: size and reduced weight, biocompatibility, safety, immunity to electromagnetic interference and high sensitivity. In a first step, wearable devices with fibre optic sensors based in Fiber Bragg gratings (FBG) were developed to be incorporated into insoles to monitor different walking parameters based on the analysis of the pressure exerted on several areas of the insole. Still within this theme, other sensors were developed using the same sensing technology, but capable of monitoring pressure and shear forces simultaneously. This work was pioneering and allowed monitoring one of the main causes of foot ulceration in people with diabetes: shear. At a later stage, the study focused on the issue related with the appearance of ulcers in people with reduced mobility and wheelchair users. In order to contribute to the mitigation of this scourge, a system was developed composed of a network of fibre optic sensors capable of monitoring the pressure at various points of the wheelchair. It not only measures the pressure at each point, but also monitors the posture of the wheelchair user and advises him/her to change posture regularly to reduce the probability of this pathology occurring. Still within this application, another work was developed where the sensor not only monitored the pressure but also the temperature in each of the analysis points, thus indirectly measuring shear. In another phase, plastic fibre optic sensors were studied and developed to monitor the body posture of an office chair user. Simultaneously, software was developed capable of monitoring and showing the user all the acquired data in real time and warning for incorrect postures, as well as advising for work breaks. In a fourth phase, the study focused on the development of highly sensitive sensors embedded in materials printed by a 3D printer. The sensor was composed of an optical fibre with a FBG and the sensor body of a flexible polymeric material called "Flexible". This material was printed on a 3D printer and during its printing the optical fibre was incorporated. The sensor proved to be highly sensitive and was able to monitor respiratory and cardiac rate, both in wearable solutions (chest and wrist) and in "invisible" solutions (office chair). Neste trabalho foram desenvolvidos e otimizados sensores em fibra ótica para aplicações biomédicas em soluções vestíveis e não intrusivas/ou invisíveis. Tendo em conta que se pretende que os dispositivos desenvolvidos não interfiram com os movimentos e o dia-a-dia do utilizador, os sensores de fibra ótica apresentam inúmeras vantagens quando comparados com os sensores eletrónicos convencionais, de entre várias, destacam-se: tamanho e peso reduzido, biocompatibilidade, segurança, imunidade a interferências eletromagnéticas e elevada sensibilidade. Numa primeira etapa, foram desenvolvidos dispositivos vestíveis com sensores de fibra ótica baseados em redes de Bragg (FBG) para incorporar em palmilhas de modo a monitorizar diferentes parâmetros da marcha com base na análise da pressão exercida em várias zonas da palmilha. Ainda no âmbito deste tema, adicionalmente, foram desenvolvidos sensores utilizando a mesma tecnologia de sensoriamento, mas capazes de monitorizar simultaneamente pressão e forças de cisalhamento. Este trabalho foi pioneiro e permitiu monitorizar um dos principais responsáveis pela ulceração dos pés em pessoas com diabetes: o cisalhamento. Numa fase posterior, o estudo centrou-se na temática relacionada com o aparecimento de úlceras em pessoas com mobilidade reduzida e utilizadores de cadeiras de rodas. De modo a contribuir para a mitigação deste flagelo, procurou-se desenvolver um sistema composto por uma rede de sensores de fibra ótica capaz de monitorizar a pressão em vários pontos de uma cadeira de rodas e não só aferir a pressão em cada ponto, mas monitorizar a postura do cadeirante e aconselhá-lo a mudar de postura com regularidade, de modo a diminuir a probabilidade de ocorrência desta patologia. Ainda dentro desta aplicação, foi publicado um outro trabalho onde o sensor não só monitoriza a pressão como também a temperatura em cada um dos pontos de análise, conseguindo aferir assim indiretamente o cisalhamento. Numa outra fase, foi realizado o estudo e desenvolvimento de sensores de fibra ótica de plástico para monitorizar a postura corporal de um utilizador de uma cadeira de escritório. Simultaneamente, foi desenvolvido um software capaz de monitorizar e mostrar ao utilizador todos os dados adquiridos em tempo real e advertir o utilizador de posturas incorretas, bem como aconselhar para pausas no trabalho. Numa quarta fase, o estudo centrou-se no desenvolvimento de sensores altamente sensíveis embebidos em materiais impressos 3D. O sensor é composto por uma fibra ótica com uma FBG e o corpo do sensor por um material polimérico flexível, denominado “Flexible”. O sensor foi impresso numa impressora 3D e durante a sua impressão foi incorporada a fibra ótica. O sensor demonstrou ser altamente sensível e foi capaz de monitorizar frequência respiratória e cardíaca, tanto em soluções vestíveis (peito e pulso) como em soluções “invisíveis” (cadeira de escritório). Programa Doutoral em Engenharia Física

People taken by upper limb disorders caused by neurological diseases suffer from grip weakening, which affects their quality of life. Researches on soft wearable robotics and advances in sensor technology emerge as promising alternatives to develop assistive and rehabilitative technologies. However, current systems rely on surface electromyography and complex machine learning classifiers to retrieve the user intentions. In addition, the grasp assistance through electromechanical or fluidic actuators is passive and does not contribute to the rehabilitation of upper-limb muscles. Therefore, this paper presents a robotic glove integrated with a force myography sensor. The glove-like orthosis features tendon-driven actuation through servo motors, working as an assistive device for people with hand disabilities. The detection of user intentions employs an optical fiber force myography sensor, simplifying the operation beyond the usual electromyography approach. Moreover, the proposed system applies functional electrical stimulation to activate the grasp collaboratively with the tendon mechanism, providing motion support and assisting rehabilitation.

In distributed shape sensing, the shape reconstruction error is more and more sensitive to the strain measuring error along with curvature radius of reconstructed shape increasing, which causes a notable challenge for large curvature radius shape reconstructing. In this paper, we demonstrate a large curvature radius shape sensing using optical frequency domain reflectometry (OFDR) in multi-core fibers. We construct a theoretical model of strain measuring error and curvature radius reconstructing errors under different curvature radius. In the experiment, by this reconstructing error model, we optimally select the measurable strain resolution and the sensing spatial resolution to realize the shape reconstruction with a large curvature radius and reconstruct two-dimensional (2D) circle shapes of curvature radii from 5 cm to 100 cm. To verify the accuracy of three-dimensional (3D) shape reconstruction, we present a 3D shape sensing validation method based on 3D printing technology. We fabricate a 3D phantom containing a groove with a variable curvature radius of 5 cm to 100 cm. The presented distributed shape sensing system realize to reconstruct this complicated 3D shape. The root-mean-square error of curvature radius between the reconstructed and designed 3D space curves is 7.2 mm and the mean Euclidean distance is 3.4 mm.

Radiofrequency ablation (RFA) is a minimally invasive form of thermotherapy with great potential in cancer care, having the capability of selectively ablating tumoral masses with a surface area of several cm2. When performing RFA in the proximity of a blood vessel, the heating profile changes due to heat dissipation, perfusion, and impedance changes. In this work, we provide an experimental framework for the real-time evaluation of 2D thermal maps in RFA neighboring a blood vessel; the experimental setup is based on simultaneous scanning of multiple fibers in a distributed sensing network, achieving a spatial resolution of 2.5 × 4 mm2 in situ. We also demonstrate an increase of ablating potential when injecting an agarose gel in the tissue. Experimental results show that the heat-sink effect contributes to a reduction of the ablated region around 30–60% on average; however, the use of agarose significantly mitigates this effect, enlarging the ablated area by a significant amount, and ablating an even larger surface (+15%) in the absence of blood vessels.

Optical fiber sensors present several advantages in relation to other types of sensors. These advantages are essentially related to the optical fiber properties, i.e., small, lightweight, resistant to high temperatures and pressure, electromagnetically passive, among others. Sensing is achieved by exploring the properties of light to obtain measurements of parameters, such as temperature, strain, or angular velocity. In addition, optical fiber sensors can be used to form an Optical Fiber Sensing Network (OFSN) allowing manufacturers to create versatile monitoring solutions with several applications, e.g., periodic monitoring along extensive distances (kilometers), in extreme or hazardous environments, inside structures and engines, in clothes, and for health monitoring and assistance. Most of the literature available on this subject focuses on a specific field of optical sensing applications and details their principles of operation. This paper presents a more broad overview, providing the reader with a literature review that describes the main principles of optical sensing and highlights the versatility, advantages, and different real-world applications of optical sensing. Moreover, it includes an overview and discussion of a less common architecture, where optical sensing and Wireless Sensor Networks (WSNs) are integrated to harness the benefits of both worlds., This work was supported by FCT—Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020.

Thermal residual strains/stresses cause several defects in hybrid structures and various studies have reported the reduction of residual strain. This paper describes a method for reducing thermal residual strains/stresses in metal-CFRP-metal hybrid tubes (MCMHT). The proposed axial preload tool provides two ways to reduce the thermal residual strains/stresses during the co-cure bonding process: pre-compressing of the metal layers and pre-stretching of the unidirectional carbon fiber reinforced polymer (CFRP) layers. An online measurement technique with embedded optical fiber Bragg grating (FBG) sensors is presented. Thermal residual strains are evaluated based on classical lamination theory with the assumption of plane stress. The theoretical calculations and measurement results agree well. Furthermore, the dynamic characteristics of the MCMHTs are tested. The results show that the reduction of residual strain increases the natural frequency of the MCMHT, but is detrimental to the damping capability of the MCMHT, which imply that the intrinsic properties of the metal-composite hybrid structure can be modified by the proposed axial preload tool.

Currently, significant progress is being made in the prevention, treatment and prognosis of many types of cancer, using biological markers to assess current physiological processes in the body, including risk assessment, differential diagnosis, screening, treatment determination and monitoring of disease progression. The interaction of protein coding gene CD44 with the corresponding ligands promotes the processes of invasion and migration in metastases. The study of new and rapid methods for the quantitative determination of the CD44 protein is essential for timely diagnosis and therapy. Current methods for detecting this protein use labeled assay reagents and are time consuming. In this paper, a fiber-optic biosensor with a spherical tip coated with a thin layer of zinc oxide (ZnO) with a thickness of 100 nm, deposited using a low-cost sol–gel method, is developed to measure the CD44 protein in the range from 100 aM to 100 nM. This sensor is easy to manufacture, has a good response to the protein change with detection limit of 0.8 fM, and has high sensitivity to the changes in the refractive index (RI) of the environment. In addition, this work demonstrates the possibility of achieving sensor regeneration without damage to the functionalized surface. The sensitivity of the obtained sensor was tested in relation to the concentration of the control protein, as well as without antibodies—CD44.

An innovative microstructured flat optical fiber is designed to obtain a multiaxial strain sensor for composite material monitoring. The sensing regions are constituted by the two eyelets where Bragg gratings are written. To achieve multiaxial sensing, a suitable microstructure is designed close to only one of the eyelets. The effect of the strain field, evaluated via a 3D finite element method approach, is considered to obtain the change of the refractive index distribution. The electromagnetic modal analysis and the coupled mode theory are exploited to evaluate the Bragg wavelength shift for the slow and fast axis fundamental modes, guided in the two eyelets and affecting the sensor response. The designed microstructured flat optical fiber is technologically feasible and promises sensing performance higher than that obtainable with the conventional optical fibers. In addition, flat optical fiber can be embedded in composite materials reducing the drawbacks related to both orientation and excess resin.

Single mode-Multimode-Single mode (SMS) sensors have been attracted a relevant attention because of their simple manufacturing, their capability of sensing different quantities, and their enhanced sensitivity compared to the most common fiber optic sensor represented by Fiber Bragg Gratings (FBGs). Moreover, SMS sensors exhibit blue-shift sensitivity to strain, opposite to FBGs, making them suitable in applications where strain-temperature cross-sensitivity may be an issue. SMS sensors are made by splicing a short multimode, preferably a two mode or quasi two-mode, optical fiber jumper between single mode pigtails. The interference of the modes propagating at different phase velocities produces a spectral pattern that shifts with temperature, strain or any perturbation of the phase difference among the modes. In this paper we review the main features of SMSs as temperature sensors and we present a potential biomedical application in an all-fiber flowmeter based on the hot-wire principle: a fiber-coupled laser source at 980 nm is used as a controllable heating source of the SMS sensor that, when immersed in fluid flow, converts the temperature variation, caused by the heat removal, into a wavelength shift of the transmitted spectrum. Thermal characterization and proof-of-concept experiments show the feasibility and functionality of the sensor and provide an outlook on possible developments and potential applications.

Metal-organic framework (MOF) nanomaterials are emerging porous coordinative polymers with large surface area and high porosity. Their application scenarios highly depend on adsorption/desorption dynamics of guest molecules in the framework. For representative ZIF-8 with framework flexibility, the study of molecule transportation in the pore channels of ZIF-8 will address the ambiguity of unclear application scenarios. In this study, the integration of lab-on-fiber technology and nanotechnology are demonstrated for real-time monitoring of adsorption/desorption dynamics of heterocyclic volatile compounds (VOCs) with kinetic diameters larger than the window aperture of ZIF-8. The in-line fiber interferometer with cascaded long-period gratings is used to monitor the real-time refractive index change of VOC adsorption/desorption. The structure-effect relationship between guest VOCs and framework flexibility is analyzed. It shows that the adsorption dynamics is highly related to the molecular geometry and kinetic diameter. The framework flexibility results in the trapping of guest VOCs toluene, pyridine, and tetrahydrofuran in the frameworks. The methanol adsorption/desorption is an effective strategy for the fast desorption of trapped residual VOCs in the framework. Finally, we conceptually demonstrated the real-time monitoring of trace toluene enrichment using ZIF-8 for indoor air purification. This study paves the way for the in-depth understanding of framework flexibility for MOF’s application.

A long period fiber grating (LPFG) sensor has been fabricated, after theoretical analysis, obtaining the maximum enhancement of the evanescent field working with the lowest order cladding mode (LP0,2 cladding mode) near turn around point. Both the wavelengths of the dual peak resonance and the coupling conditions of the mode have been analyzed in detail. A flow cell has been fabricated to characterize the sensor in term of surrounding refractive index (SRI) sensitivity. The sensitivity of the sensor resulted to be ~ 8751 nm/SRIU, with a resolution in the order of 10-5, within the SRI range of 1.333 to 1.3335.

In recent years, numerous measurement techniques have been employed to characterize surface textures in the micrometer and nanometer range. Although these techniques have enabled significant advances in surface metrology, larger surface details are not easily measurable with such techniques. We propose a simple and reliable fiber Bragg grating (FBG) based tactile displacement sensor to measure a wide range of displacements that vary from $0.2~\mu \text{m}$ to 2mm. The device adopts a novel multi-pivot mechanical lever-based amplification mechanism to achieve a wide measurement range. Experimental results show that the sensor can measure both 219nm thick, thin-film coating and 1.22mm glass slide by selecting an appropriate pivot position. Further, the device is employed to identify topographies of three different surfaces of different dimensions. The sensor’s optimized configuration demonstrates an excellent displacement sensitivity of 63926pm/mm with a high resolution of 15.64nm. The repeatability of the sensor in this configuration is 2.44%.

First order cutaneous neurons allow object recognition, texture discrimination, and sensorimotor feedback. Their function is well-investigated under passive stimulation while their role during active touch or sensorimotor control is understudied. To understand how human perception and sensorimotor controlling strategy depend on cutaneous neural signals under active tactile exploration, the finite element (FE) hand and Izhikevich neural dynamic model were combined to predict the cutaneous neural dynamics and the resulting perception during a discrimination test. Using in-vivo microneurography generated single afferent recordings, 75% of the data was applied for the model optimization and another 25% was used for validation. By using this integrated numerical model, the predicted tactile neural signals of the single afferent fibers agreed well with the microneurography test results, achieving the out-of-sample values of 0.94 and 0.82 for slowly adapting type I (SAI) and fast adapting type I unit (FAI) respectively. Similar discriminating capability with the human subject was achieved based on this computational model. Comparable performance with the published numerical model on predicting the cutaneous neural response under passive stimuli was also presented, ensuring the potential applicability of this multi-level numerical model in studying the human tactile sensing mechanisms during active touch. The predicted population-level 1st order afferent neural signals under active touch suggest that different coding strategies might be applied to the afferent neural signals elicited from different cutaneous neurons simultaneously.

Mención Internacional en el título de doctor Light is a very useful tool for measuring high frequency and low amplitude mechanical vibrations. Thanks to the interference process and under certain circumstances we can obtain a specific sort of optical sources called multimode multiheterodyne sources, that are very useful to read several optical wavelengths at the same time on a single photodetector and distinguishing them from each other. This characteristic makes them suitable for interrogating fiber optic sensors. In this thesis, I analyze several fiber optic sensor readout methods that mix multiheterodyne techniques, multimode techniques, and interferometry techniques to measure ultrasound and acoustic mechanical waves. These mechanical waves occur when periodic forces are applied to mechanical structures. This disturbs the layout of atoms and may lead to cracks or the complete collapse of the structure. Therefore, the characterization and measurement of such vibrations are of great importance when performing structure health monitoring (SHM) and non-destructive evaluation (NDE). This thesis aims to solve this problem by implementing several systems that employ light-based technology to measure and characterize mechanical vibrations up to 1 MHz of frequency and sub-nano-strain (lower than 10-3 ppm) level of resolution. The proposed systems involve new features and parameters more settable compared to more conventional approaches of optical sensor reading processes and therefore they offer wider possibilities. A total of three systems have been implemented and tested: First, an electro-optic dual optical frequency comb source to read fiber Bragg gratings for dynamic measurements. This set up reaches 120 kHz of mechanical frequency detection. The second system is based on a self-heterodyne acousto-optic comb that reads a random fiber grating sensor. In this case, the system can detect up to 1 MHz of mechanical vibrations. Finally, the third is based on a compact electro-optic dual optical frequency comb that is used to read low reflectivity fiber Bragg gratings with a dispersion interferometer. This system can detect a maximum of 135 kHz of mechanical frequencies. The results of this thesis improve previous systems achievements to satisfy the specifications required to date in this application, both in mechanical bandwidth and in strain amplitude. They also show the potential of these multimode sources for high-precision optical sensing. La luz es una herramienta muy útil para medir vibraciones mecánicas de alta frecuencia y baja amplitud. Gracias al proceso de interferencia y bajo determinadas circunstancias podemos obtener un tipo específico de fuentes ópticas, denominadas fuentes multimodo multiheterodinas, que son muy útiles para leer varias longitudes de onda ópticas al mismo tiempo en un solo fotodetector y distinguirlas entre sí. Esta característica hace que estas fuentes ópticas sean adecuadas para la lectura de sensores de fibra óptica. En esta tesis, analizo varios métodos de lectura de sensores de fibra óptica que mezclan técnicas multiheterodinas, técnicas multimodo y técnicas de interferometría para medir ultrasonidos y ondas mecánicas acústicas. Estas ondas mecánicas se producen cuando se aplican fuerzas periódicas a las estructuras mecánicas. Esto perturba la disposición de los átomos y puede provocar grietas o el colapso completo de la estructura. Por lo tanto, la caracterización y medida de dichas vibraciones son de gran importancia a la hora de monitorizar el estado de las estructuras y de realizar una evaluación no destructiva. Esta tesis tiene como objetivo resolver este problema mediante la implementación de varios sistemas que emplean tecnología basada en la luz para medir y caracterizar vibraciones mecánicas hasta frecuencias de 1 MHz y nivel de resolución sub-nano-deformación (menor que 10-3 ppm). Los sistemas propuestos implican nuevas características y parámetros más configurables en comparación con los enfoques más convencionales de procesos de lectura de sensores ópticos y, por lo tanto, ofrecen posibilidades más amplias. A lo largo de la tesis se presentan tres sistemas de medida: El primero está basado en un doble peine de frecuencias ópticas (dual comb) electroóptico que es capaz de leer sensores de fibra óptica basados en redes de Bragg (FBG) en régimen dinámico. Este sistema ha sido probado con una frecuencia máxima de detección de 120 kHz. En segundo lugar, se presenta un sistema basado en un selfheterodyne comb acustoóptico para leer sensores de fibra con distribución aleatoria de la rejilla en el núcleo (random grating). Este sistema es capaz de detectar señales de vibración de hasta 1 MHz. El tercer sistema presentado se basa en un doble peine de frecuencias ópticas (dual comb) electroóptico compacto que se utiliza para leer sensores FBG de baja reflectividad con un interferómetro de dispersión. Este sistema puede detectar hasta 135 kHz de vibraciones mecánicas. Los resultados de esta tesis mejoran los obtenidos en sistemas anteriores a fin de satisfacer las especificaciones requeridas hasta la fecha en esta aplicación, tanto en el ancho de banda mecánico como en la amplitud de la deformación. También muestran el potencial de estas fuentes multimodo para la detección óptica de alta precisión. Quiero agradecer la financiación de este trabajo dada por el Ministerio de Educación, Cultura y Deporte para la Formación de Profesorado Universitario FPU2016 (Beca FPU16/03695) y a través del proyecto PARAQUA (TEC2017-86271-R), así como por el Ministerio de Ciencia, Innovación y Universidades a través de las ayudas de movilidad EST18/00617. Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de Madrid Presidente: Óscar Esteban Martínez.- Secretario: Marta Ruiz Llata.- Vocal: Pedro Alberto da Silva Jorge

Fiber optofluidic laser (FOFL) integrates optical fiber microcavity and microfluidic channel and provides many unique advantages for sensing applications. FOFLs not only inherit the advantages of lasers such as high sensitivity, high signal-to-noise ratio, and narrow linewidth, but also hold the unique features of optical fiber, including ease of integration, high repeatability, and low cost. With the development of new fiber structures and fabrication technologies, FOFLs become an important branch of optical fiber sensors, especially for application in biochemical detection. In this paper, the recent progress on FOFL is reviewed. We focuse mainly on the optical fiber resonators, gain medium, and the emerging sensing applications. The prospects for FOFL are also discussed. We believe that the FOFL sensor provides a promising technology for biomedical analysis and environmental monitoring.

In this article, two configurations are presented for simultaneous measurement of strain and temperature by reducing the cross-section area in small regions of the fiber where the Bragg gratings were inscribed, to achieve dual sensitivity to strain and handle the cross-sensitivity to temperature of a single grating. Each configuration used a single Bragg grating inscribed in a 2-ring undoped poly (methyl methacrylate) microstructured polymer optical fiber (mPOF) with a pulsed Q-switched Nd:YAG laser system. To reduce the cross-section area, a femtosecond laser system was used to remove portions of the mPOF, creating micromachined slots in the fiber, with different lengths for each configuration. The result was the appearance of a second peak when strain is applied, with a higher strain sensitivity. The thermal, humidity and refractive index response of these gratings were analyzed, revealing a thermal sensitivity almost twice the value of a common Bragg grating inscribed in the same mPOF. The maximum root mean square errors obtained when both strain and temperature are applied in these grating devices were 52 μϵ and 0.6 °C, respectively. These results show that the method used to produce these devices could be a suitable and reliable option to fabricate very compact sensors to simultaneously measure strain and other parameters, such as temperature. Moreover, these devices may be used as phase-shift gratings since the position of the reflective peaks and their relative spectral separation may be modulated by applying strain to the optical fiber.

In this work, a novel optical fiber sensor capable of measuring both the liquid level and its refractive index is designed, manufactured and demonstrated through simulations and experimentally. For this, a silica capillary hollow-core fiber is used. The fiber, with a sensing length of 1.55 mm, has been processed with a femtosecond laser, so that it incorporates four holes in its structure. In this way, the liquid enters the air core, and it is possible to perform the sensing through the Fabry-Perot cavities that the liquid generates. The detection mode is in reflection. With a resolution of 4 μm (liquid level), it is in the state of the art of this type of sensor. The system is designed so that in the future it will be capable of measuring the level of immiscible liquids, that is, liquids that form stratified layers. It can be useful to determine the presence of impurities in tanks. This work was supported by the Ministerio de Economía y Competitividad of Spain (TEC2016-76021-C2-1-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (PID2019-107270RB-C21 and PID2019-107270RB-C22), the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797), and Projects for young researches UPNA 2019. The authors also thank the INESC-Porto colleagues for the fiber sample used in the experiments.

Moving differential and dynamic window moving averaging are simple and well-known signal processing algorithms. However, the most common methods of obtaining sufficient signal-to-noise ratios in distributed acoustic sensing use expensive and precise equipment such as laser sources, photoreceivers, etc., and neural network postprocessing, which results in an unacceptable price of an acoustic monitoring system for potential customers. This paper presents the distributed fiber-optic acoustic sensors data processing and noise suppression techniques applied both to raw data (spatial and temporal amplitude distributions) and to spectra obtained after the Fourier transform. The performance of algorithms’ individual parts in processing distributed acoustic sensor’s data obtained in laboratory conditions for an optical fiber subjected to various dynamic impact events is studied. A comparative analysis of these parts’ efficiency was carried out, and for each type of impact event, the most beneficial combinations were identified. The feasibility of existing noise reduction techniques performance improvement is proposed and tested. Presented algorithms are undemanding for computation resources and provide the signal-to-noise ratio enhancement of up to 13.1 dB. Thus, they can be useful in areas requiring the distributed acoustic monitoring systems’ cost reduction as maintaining acceptable performance while allowing the use of cheaper hardware.