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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.

no. 760801\NEMOSINE UID/QUI/50006/2020 Preserving culture heritage cellulose acetate-based historical films is a challenge due to the long-term instability of these complex materials and a lack of prediction models that can guide conservation strategies for each particular film. In this work, a cellulose acetate degradation model is proposed as the basis for the selection of appropriate strategies for storage and conservation for each specimen, considering its specific information. Due to the formulation complexity and diversity of cellulose acetate-based films produced over the decades, we hereby propose a hybrid modeling approach to describe the films degradation process. The problem is addressed by a hybrid model that uses as a backbone a first-principles based model to describe the degradation kinetics of the pure cellulose diacetate polymer. The mechanistic model was successfully adapted to fit experimental data from accelerated aging of plasticized films. The hybrid model considers then the specificity of each historical film via the development of two chemometric models. These models resource on gas release data, namely acetic acid, and descriptors of the films (manufacturing date, AD-strip value and film type) to assess the current polymer degradation state and estimate the increase in the degradation rate. These estimations are then conjugated with storage conditions (e.g., temperature and relative humidity, presence of adsorbent in the film’s box) and used to feed the mechanistic model to provide the required time degradation simulations. The developed chemometric models provided predictions with accuracy more than 87%. We have found that the storage archive as well as the manufacturing company are not determining factors for conservation but rather the manufacturing date, off gas data as well as the film type. In summary, this hybrid modeling was able to develop a practical tool for conservators to assess films conservation state and to design storage and conservation policies that are best suited for each cultural heritage film. publishersversion published

[EN] In this work, we obtained chirped Bragg gratings by post-coating uniform poly (methylmethacrylate) (PMMA) microstructured polymer optical fiber Bragg gratings (POFBGs) with an UV cure adhesive. The main advantage of the proposed method consists on being a cost-effective and simple solution, since no special phase mask, addi tional etching or gradient thermal annealing are required. A comparison between the fabricated chirped Bragg grating¿s performance and previous reported methods in the literature is presented. As a compact sensor with two different active areas (adhesive coated and uncoated sections of the POFBG), the developed sensing device can be used for multiparameter sensing, namely for strain, humidity and temperature monitoring. Allying the proposed flexible and low-cost fabrication technique with the intrinsic characteristics of POFs, one may conclude that the developed sensor has high potential for multiparameter sensing in possible future engineering and biomedical applications., National Natural Science Foundation of China (62003046) ; The Spanish Ministerio de Ciencia, Innovacion y Universidades RTI2018-101658-B-I00 FOCAL Project; Guangdong Basic and Applied Basic Research Foundation (2021A1515011997) ; Guangdong Recruitment Program of Foreign Experts (2020A1414010393) ; C. Marques ac-knowledges Fundacao para a Ciencia e a Tecnologia (FCT) through the CEECIND/00034/2018 (iFish project) and this work was developed within the scope of the project i3N, UIDB/50025/2020 &UIDP/50025/2020, financed by national funds through the FCT/MEC. Luis Pereira and Tiago Paixao also acknowledge FCT for the grant with references SFRH/BD/146295/2019 and PD/BD/128265/2016, respectively.

In this work, a network of fiber sensors has been developed for real time, in situ, and in operando multipoint monitoring the surface temperature distribution on a smartphone Li-ion battery (LiB). Different temperature and relative humidity conditions are considered, in order to mimic the LiB response in the dry, temperate, and cold climates. In total, the temperature variations that occur in five different locations of the LiB are monitored, during constant current charge and different discharge rates, under normal and abusive operating conditions, performing a thermal spatial mapping of the battery surface. In general, the sensors detect temperature variations according to the voltage signal change and faster variations of voltage usually translate in higher temperature rise at the LiB surface. For instance, under abusive discharge, where the voltage drop is fast, the temperature increases at least twice when compared to the normal operating conditions. Absolute temperature values as high as (65.0 ± 0.1) °C are detected by the optical sensor located near the electrodes, under the higher discharge rate (5.77 C) and dry climate. A thermal gradient is identified from the top to the bottom on the LiB surface during the experimental tests. A lower battery performance is observed when it operates under the cold climate, with maximum temperature variations of (30.0 ± 0.1) °C for the higher discharge rate. These results can be helpful to design of next generation of LiBs, improving a faster cooling in critical areas, in order to reduce accumulated heat and preventing consequences such as thermal runaway and failure.

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.

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A fiber s pecklegram s ensor b ased o n d eep l earning t o p redict a xial strains on a polymer optical fiber is proposed. The resultant model permits the construction of a calibration curve with extended dynamic range.

This scientific research investigates the behavior of two incompressible fluids in a micro-T-junction channel by means of a computational simulation through the physical properties of water and air and the discretization of conservation equations for the dispersed phases. It was possible to represent different regimes of droplets formation in the computational domain. OpenFOAM version 4.0.1 software is an open platform used in the academic environment for fluid dynamic simulations and was chosen to perform the flow’s numerical simulations due to its great acceptance in the scientific environment . The InterFOAM solver using the VOF method (Volume Of Fluid) developed for computational simulations of multi-phase flows was adopted in the simulations studied here. This study develops a comparative analysis of the droplet’s formation behavior at the injection time and evaluates the flow aspect of the dispersed phase through the continuous phase in the main channel. From the variations in the flow rates, it was possible to verify the flow phases’ dependence in determining the flow regime. This research was developed based on a literature review and evaluates the bubble injection shape and droplet coalescence in a T-junction microchannel. The results were compared with the literature data.

UIDB/04028/2020 UIDP/04028/2020 UID/QUI/50006/2019 A deep understanding of the degradation of cellulose diacetate (CDA) polymer is crucial in finding the appropriate long-term stability solution. This work presents an investigation of the reaction mechanism of hydrolysis using electronic density functional theory calculations with the B3LYP/6-31++G*∗ level of theory to determine the energetics of the degradation reactions. This information was coupled with the transition-state theory to establish the kinetics of degradation for both the acid-catalyzed and noncatalyzed degradation pathways. In this model, the dependence on water concentration of the polymer as a function of pH and the evaporation of acetic acid from the polymer is explicitly accounted for. For the latter, the dependence of the concentration of acetic acid inside the films with the partial pressure on the surrounding environment was measured by sorption isotherms, where Henry's law constant was measured as a function of temperature. The accuracy of this approach was validated through comparison with experimental results of CDA-accelerated aging experiments. This model provides a step forward for the estimation of CDA degradation dependence on environmental conditions. From a broader perspective, this method can be translated to establish degradation models to predict the aging of other types of polymeric materials from first-principles calculations. publishersversion published

Strain and temperature are critical parameters to monitor in Li-ion batteries (LIBs) to improve their safety and long-term cycling stability. High local current densities can result in a massive heat release, decomposition of the electrolyte, gas evolution and even explosion of the battery cell, known as thermal runaway. However, the corrosive chemical environment in the batteries is a challenge to monitor strain and temperature. Optical fiber sensors, due to their high chemical stability and small diameter, can be embedded within the LIBs, thus becoming an interesting solution for operando and in situ measurements. In this work, a hybrid sensing network constituted by fiber Bragg gratings and Fabry-Perot cavities is proposed for the discrimination of strain and temperature. The proof-of-concept was performed by attaching the sensing network to the surface of a smartphone battery. Afterwards, it was embedded in a Li-ion pouch cell to monitor and simultaneously discriminate internal strain and temperature variations in three different locations. Higher thermal and strain variations are observed in the middle position. The methodology presented proves to be a feasible and non-invasive solution for internal, real-time, multipoint and operando temperature and strain monitoring of LIBs, which is crucial for their safety.

Nitric oxide (NO) is one of the smallest endogenous molecules with particularly interesting aspects roles in biological systems, despite its toxicological potential. Solid carriers have potential biomedical interest in the delivery of exogenous NO for anti-bacterial, anti-thrombic and wound healing applications. In this work, we prepared nanoporous materials from clay based solids, of montmorillonite type, with the main goal of studying its potential in the field of storage and release of nitric oxide for therapeutic applications. Materials were characterized by X-ray diffraction, nitrogen adsorption at −196 °C, TG-DSC and chemical analysis. The kinetic data for the nitric oxide storage and release, in selected materials, was obtained in gas and liquid phases. The released amounts of NO in the liquid phase were within the biological range and, for some materials, a slow release kinetics was obtained with, inclusively, an almost direct relation between the released fraction and time. Toxicological assays with HeLa cells indicated that the materials have low cytotoxicity.

This paper focuses on three main issues regarding Material Extrusion (MEX) Additive Manufacturing (AM) of thermoplastic composites reinforced by pre-functionalized continuous Nickel&ndash, Titanium (NiTi) wires: (i) Evaluation of the effect of the MEX process on the properties of the pre-functionalized NiTi, (ii) evaluation of the mechanical and thermal behavior of the composite material during usage, (iii) the inspection of the parts by Non-Destructive Testing (NDT). For this purpose, an optical fiber sensing network, based on fiber Bragg grating and a cascaded optical fiber sensor, was successfully embedded during the 3D printing of a polylactic acid (PLA) matrix reinforced by NiTi wires. Thermal and mechanical perturbations were successfully registered as a consequence of thermal and mechanical stimuli. During a heating/cooling cycle, a maximum contraction of &asymp, 100 &micro, m was detected by the cascaded sensor in the PLA material at the end of the heating step (induced by Joule effect) of NiTi wires and a thermal perturbation associated with the structural transformation of austenite to R-phase was observed during the natural cooling step, near 33.0 &deg, C. Regarding tensile cycling tests, higher increases in temperature arose when the applied force ranged between 0.7 and 1.1 kN, reaching a maximum temperature variation of 9.5 &plusmn, 0.1 &deg, C. During the unload step, a slope change in the temperature behavior was detected, which is associated with the material transformation of the NiTi wire (martensite to austenite). The embedded optical sensing methodology presented here proved to be an effective and precise tool to identify structural transformations regarding the specific application as a Non-Destructive Testing for AM.

In this work, the thermo-optic coefficient (TOC) of ethanol-water mixtures, through refractive index and temperature measurements are determined using an etched optical fiber tip based on a multimode interferometer. The proposed probe is fabricated by fusion-splicing a 5.2 mm long coreless fiber section to a single mode fiber. To reduce the sensor dimensions and improve its sensitivity towards external medium variations, the fiber tip is subjected to wet chemical etching using a solution of 40% hydrofluoric acid, presenting a final diameter of 24.4 μm. The TOC of each solution is estimated and, in the case of deionized water and pure ethanol, its value is of −1.128 × 10−4 °C−1 and −3.117 × 10−4 °C−1, respectively.

A fiber sensor based on a Fabry–Perot cavity is reported for measuring mixtures of water and glycerin. The sensor is fabricated by producing an air bubble near the end face of a multimode fiber section, and reshaping the tip in order to produce a thin silica diaphragm. It is observed that there is dependence between diaphragm dimensions and the structure sensitivity. The sensor with a 20 μm thick diaphragm presents a sensitivity of 7.81 pm/wt.% regarding the variation of water mass fraction in glycerin. With this sensing head, an experimental resolution of 2.5 wt.% is estimated. By converting the mass fraction into refractive index variations, a maximum sensitivity of 5.49 nm/RIU is obtained. Moreover, given the low-temperature sensitivity (1.6 pm/ °C), the proposed cavity should be adequate to perform temperature independent measurements. The purity degree of glycerin is one of the most important parameters to be determined in applications such as in pharmaceutical or cosmetic area. The proposed sensor can be an alternative to the previously developed ones.

A reflective fiber optic sensor based on multimode interference for the measurement of refractive index variations in glucose aqueous solutions is proposed. The sensor is fabricated by splicing a short section of coreless silica fiber to standard single mode fiber. The influence of the coreless fiber dimensions on the sensor performance is analyzed. By changing the sensor length, no significant impact is observed. However, the reduction of the sensing head diameter leads to a large improvement of the sensitivity. The smaller sensor, with a length of 5 mm and a diameter of 24 μm, presents a maximum sensitivity of 1467.59 nm/RIU, for the refractive index range between 1.364 and 1.397 RIU. Taking into account the acquisition system, a maximum theoretical resolution of 6.8 × 10 -5 RIU is achieved.

Presence of reactive oxides, such as sodium, potassium, and magnesium oxides, compromise the pozzolanic activities of mineral additions to cement-based materials. That is because these oxides react with water to form hydroxides. Subsequently, these hydroxides may react with the otherwise non-reactive oxides, such as silicon and aluminum oxides, to form various silicate and aluminate phases in the cement-based material, that finally compete with the desired CSH phase. Further, the strong pozzolanic activity of the silica fume is seemingly due to its large ability to form the calcium silicate hydrated systems when compared with both metakaolin and fly ashes. All these results have been established by X-ray fluorescence, microstructural, and chemometric analyses that were applied to investigate the pozzolanic activities, thermodynamic, structural, and mechanical properties of a set of mineral systems widely applied to cement-based materials (silica fume, metakaolin, and fly ashes). The chemometric analyses revealed that the materials prepared with silica fume exhibited the largest mechanical properties, whereas the reference the lowest. The cement-based materials with metakaolin and fly ashes present intermediary resistances and similar behaviors. In conclusion, strict control of the purity of the material always needs to be performed to obtain mineral systems with powerful pozzolanic activities.

Thermodynamic, microstructural, chemometrics, and analyses of mechanical properties of cement-based materials are performed with the addition of agro-industrial residues, which are often discarded in landfills. In this sense, two types of waste ashes of sugarcane bagasse were investigated. All investigated materials were characterized by XRF, TGA, XRD, and SEM/EDS analyses. The experiments of XRF data revealed that the ash additions increased the presence of reactive inorganic compounds, such as K2O, in the mixture of concrete ingredients. Subsequently, thermodynamic properties revealed that the complex hydration reactions associated with the processing of the concrete admixture are spontaneous processes (ΔrG ~ −400 kJ.mol−1). Further, XRD and SEM/EDS data showed that the hydrated waste ashes presented elevated quantities of amorphous phases. For all concretes, the presence of the main cementitious amorphous phase CSH was detected. Finally, chemometric analysis of the axial compressive strength and tensile resistances of the cement-based materials revealed that, after 365 days, the ashes could be used as partial cement substitutes that typically emit CO2 when applied to constructions.

This work shows a comparative study between the thermocouples and fiber sensors response for the monitoring of temperature variations occurring in three different locations of a lithium battery. The battery is submitted to constant current charge and different discharge rates, under normal and abusive operating conditions. For this specific application, the results show that the fiber Bragg grating sensors have better resolution and a rise time 28.2% lower than the K‐type thermocouples, making them a better choice for the real time monitoring of the battery surface temperature as well as a useful tool for failure detection and an optimized management in batteries.

A Fabry-Perot air bubble microcavity fabricated between a section of single mode fiber and a multimode fiber that requires only the use of a commercial fusion splicer is proposed. The study of the microcavities growth with the number of applied arcs is performed and several sensors are tested. The sensors are tested for lateral load measurements, and it is observed that there is dependence between the sensor dimensions and its sensitivity. The maximum sensitivity of 2.11 nm/N was obtained for the 161-μm-long cavity. Moreover, given the low temperature sensitivity (

Periodic mesoporous organosilicas (PMO), with phenylene or biphenylene organic linkers, were thermally treated in flowing nitrogen atmosphere upon different conditions aiming the enhancement of their CO2 adsorption/separation properties. As-synthesized and template-extracted phenylene- and biphenylene-PMO were pyrolysed at 800 and 1200 °C. The effects of: i) the type of organic bridge; ii) the presence of nitrogen atoms; iii) the use of an acid catalyst prior to carbonization; and iv) pore size were investigated. It was found that pyrolysis promotes modifications in the physical-chemical and the textural properties of the PMO materials, being the formation of micropores one of the most notable differences. Furthermore, with the exception of biphenylene-PMO, the molecular-scale periodicity of the materials was strongly affected by the pyrolysis treatment probably as a result of SiC bond cleavage. The CO2 adsorption capacity and the selectivity for CO2/CH4 separation of all pyrolysed materials were enhanced. In general, the increase of the microporosity in the pyrolysed PMO is accompanied by an improvement of the CO2 adsorption properties with concomitant reduction of the CH4 adsorption behavior. The most interesting material for CO2/CH4 separation is the biphenylene-PMO pyrolysed at 1200 °C, with a selectivity of 9.5 at 25 °C and 500 kPa.

The synthesis and structural characterization of two isostructural metal (M=Ni, Co) 3D framework structure that integrate vitamin B3 building blocks with NO delivery capabilities and low toxicity is presented. The compounds with a formula [M2(μ2-H2O)(μ-vitamin B3)4]·2H2O contain two crystallographic distinct divalent metal centres connected by a bridging water and carboxylate group from vitamin B3. The porous compounds have the capability of storing and releasing nitric oxide (NO) in a slow and reversible manner, with released amounts of 2.6 and 2.0μmol NOmgsolid-1, on the Ni and Co compound, respectively. The NO release followed a convenient slow release kinetic profile in both gas and liquid phases. Haemoglobin tests demonstrated that NO is released to the medium in a biologically active form, thus suitable to trigger the desired response in biological systems. The toxicity of the samples with and without loaded NO was evaluated from cytotoxicity tests in HeLa and HEKn cells, showing low toxicity of the compounds at concentrations below 180μgcm-3. The overall results indicate that these bio based MOFs are of interest for therapeutic applications related with NO delivery. STATEMENT OF SIGNIFICANCE.

This chapter focuses on new compositions of thermoplastic matrices and reinforcements to process by fused deposition modelling (FDM). The available materials for this additive manufacturing (AM) technique are generally limited to PLA—polylactic acid, ABS—acrylonitrile butadiene styrene and PA—polyamide (NYLON®) with temperature gradients and mechanical behaviours that are not suited for high-performance applications, such as aeronautics and automotive sector. In this work, an intensive research was made in order to evaluate mechanical, thermal and rheological properties considered important for 3D printing of commercial filaments. Results aided in the selection of high-performance reinforced materials for AM. Advanced polymers, such as PEEK—polyether ether ketone and PA66—polyamide 66, were the matrices chosen to produce high service nanocomposite formulations, each with varying amounts of multi-wall carbon nanotubes (MWCNTs). The resulting feedstock materials were characterized using the same techniques as the commercial filaments. Preliminary tests with printed parts of these composites were made in pursuance of their optimal printing parameters to undergo an experimental hybrid system (EHS).

[EN] FBG in polymer optical fibers (POFs) is a promising technology for a wide range of sensing applications due to a lower Young¿s modulus and a large range of applying strain. Furthermore, POFs have several properties which make them attractive for biosensing applications such as nonbrittle nature, flexibility in bending and biocompatibility. Chirped Fiber Bragg gratings (CFBGs), which are characterized by a nonuniform modulation of the refractive index show a broad reflection spectrum, enabling shortlength distributed sensing. The combining benefits of POF and CFBGs is attractive for biomedical applications. Here, we present a novel method to obtain CFBG in POF with a postprocess uniform POF FBG by using resin., The Spanish Ministerio de Ciencia, Innovación y Universidades RTI2018­101658­B­I00 FOCAL Project; National Natural Science Foundation of China (61435006, 61525502); The Science and Technology Planning Project of Guangdong Province (2017B010123005, 2018B010114002); Local Innovation and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01X121). This work was developed within the scope of the project i3N, UIDB/50025/2020 & UIDP/50025/2020, financed by national funds through the FCT/MEC. Luís Pereira and Tiago Paixão acknowledge FCT for the grants SFRH/BD/146295/2019 and PD/BD/128265/2016, respectively. This work is also funded by national funds (OE), through FCT¿I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree­Law 57/2016, of August 29, changed by Law 57/2017, of July 19.

We present the first Bragg gratings fabricated in two, three and five rings undoped PMMA microstructured polymer optical fibres (mPOFs) with relative low cost 266 nm Nd:YAG laser in the 850 nm region. The fibers were connectorised with commercial ferrules for easy coupling with silica patch cables. Temperature, humidity and strain sensitivities are measured and also the impact of ring structure and the diameter of POF on the characterization measurements are studied for potential applications. We also analyzed the effect of the number of hexagonal rings structure in gratings fabrication, noticing that larger number of rings lead to more difficulties to obtain strong gratings, where we consider this performance due to the scattering effects. We demonstrate Bragg gratings fabrication in 5-rings structure mPOF after 6 min by using 266 nm Nd:YAG laser whereas no Bragg gratings have been fabricated so far using 325 nm He-Cd laser system. Up to 30 dB relative reflected power gratings are obtained in two rings mPOF, showing good time stability and promising results for undoped mPOF applications.

In this work, an inline sensor based on a double antiresonant hollow core fiber is proposed for the simultaneous measurement of refractive index and temperature. The fiber, consisting of four silica capillaries with wall thickness of ~1.5 um and a cladding with a thickness of ~36.5 um, is spliced between two sections of single mode fiber. The spectral behavior, measured in transmission, results from the combination of different frequencies which enable the discrimination between the two parameters. The sensing head is subjected to refractive index measurements using aqueous solutions with different concentrations of ethanol. For a sensor with a length of ~10 mm, and considering the lower frequency signal, the sensitivity to refractive index is 389.6 nm/RIU, whereas for the higher frequency, the sensitivity attained is 2.8 nm/RIU. On the other hand, the sensing head presented a sensitivity to temperature of 25.5 pm/K and -27.6 pm/K for the higher and lower frequencies, respectively. published

A series of zirconium dicarboxylate-based metal-organic frameworks (Zr MOFs) of the UiO-66 (tetrahedral and octahedral cages) or MIL-140 (triangular channels) structure type were investigated for the separation of ethane/ethylene mixtures. The adsorption, investigated both experimentally and computationally, revealed that the size and type of pores have a more pronounced effect on the selectivity than the aromaticity of the linker. The increase in pore size when changing from benzene to naphthalene (NDC) dicarboxylate ligand makes UiO-NDC less selective (1.3-1.4) than UiO-66 (1.75-1.9) within the pressure range (100-1000 kPa), while the three-dimensional (3D) pores of the UiOs favor the adsorption of ethane due to the interactions between ethane with more spacers than in the case of the 1D channels of MIL-140s. The impact of the functionalization revealed a very interesting increase of selectivity when two perfluoro groups are present on the aromatic ring (UiO-66-2CF3) (value of 2.5 up to 1000 kPa). Indeed, UiO-66-2CF3 revealed a unique combination of selectivity and working capacity at high pressures. This is due to a complex adsorption mechanism involving a different distribution of the guest molecules in the different cages associated with changes in the ligand/perfluoro orientation when the pressure increases, favoring the ethane adsorption at high pressures.

A reflective fiber optic sensor based on multimode interference for the measurement of relative humidity (RH) is proposed and experimentally demonstrated. The proposed probe is fabricated by fusion-splicing, approximately 30 mm long coreless fiber section to a single mode fiber. A hydrophilic agarose gel is coated on the coreless fiber, using the dip coating technique. When the incident light comes from the SMF to the CSF, the high-order modes are excited and propagate within the CSF. These excited modes interfere with one another as they propagate along whole CSF length, giving rise to a multimode interference (MMI). Since the effective refractive index of the agarose gel changes with the ambient relative humidity, as the environmental refractive index changes, the propagation constants for each guided mode within the CSF will change too, which leads to shifts in the output spectra. The proposed sensor has a great potential in real time RH monitoring, exhibiting a large range of operation with good stability. For RH variations in the range between 60 %RH and 98.5 %RH, the sensor presents a maximum sensitivity of 44.2 pm/%RH, and taking in consideration the interrogation system, a resolution of 1.1% RH is acquired. This sensor can be of interest for applications where a control of high levels of relative humidity is required. published

A hybrid sensor based on microstructured hollow core fiber is proposed for the simultaneous measurement of strain and temperature. The fiber, consisting of four silica capillaries with wall thickness of ~1 μm and a cladding with a thickness of ~26 μm, is spliced between two sections of single mode fiber. Using a low arc discharge power to splice the two fibers, a Fabry-Perot interferometer is formed. In this situation, light travels in the hollow core and the behavior of a twowave interferometer is observed. However, when the power of the arc discharge is increased, the structure near the splice area changes, generating new interferometric paths and giving rise to a different spectral response. In this work, sensors with a single degenerated area are analyzed. In such case, both Fabry-Perot and Michelson interferometers are created and different sensitivities to strain and temperature are obtained. The different spectral frequencies are analyzed, enabling the discrimination between the two parameters. For a sensor with a length of ~385 μm, strain sensitivities of 2.46 pm/μe and -0.52 pm/μe are obtained for the Fabry-Perot and for the Michelson interferometer, respectively. Regarding temperature, a sensitivity of 1.81 pm/°C was attained for the former, whereas for the last the sensitivity was of 42.23 pm/°C. Keywords: Hyb

Highlights • Cortisol detection based on surface plasmon resonance (SPR) using an unclad plastic optical fiber (POF). • High sensitivity and low limit of detection (LOD). • Selectivity of the proposed sensor for stress hormone was performed showing high specificity. • Optical sensor solution with relatively low-cost interrogation method, straightforward signal processing. • Interesting working range (0.005−10 ng/mL) for different biological samples from human or marine life., This paper presents the development and feasibility tests of a cortisol immunosensor. The sensor is based on surface plasmon resonance (SPR) using an unclad plastic optical fiber (POF) in which the SPR is used as sensitivity enhancer, promoted by a gold/palladium (AuPd) alloy coating. The AuPd coated fibers were functionalized with an anti-cortisol antibody and passivated with bovine serum albumin (BSA) to be tested in the presence of cortisol as target analyte. The antibody-antigen binding reaction caused a variation of the refractive index on the surface of the AuPd coating, which leads to a shift of the SPR signature wavelength. The sensor was tested for different cortisol concentrations, ranging from 0.005 to 10 ng/mL. The reported biosensor presented a total wavelength shift of 15 nm for the testing range, putting in evidence a high sensitivity. Control tests for selectivity assessment were also performed. Concentrations as high as 10 ng/mL of cortisol, in a sensor functionalized with anti-hCG antibodies, only resulted in 1 nm variation of the resonance wavelength, 15 times lower than the one functionalized with the anti-cortisol antibodies, which indicates a high selectivity for the proposed approach. For this sensing approach the limit of detection (LOD) was determined to be 1 pg/mL. The proposed SPR based POF sensor has a low-cost interrogation method, high sensitivity and low LOD, straightforward signal processing and find important applications in different biological fields.

Monolithic carbon foams with hierarchical porosity were prepared from polyurethane templates and resol precursors. Mesoporosity was achieved through the use of soft templating with surfactant Pluronic F127, and macroporosity from the polyurethane foams was retained. Conditions to obtain high porosity materials were optimized. The best materials have high specific surface areas (380 and 582 m2 g–1, respectively) and high electrical conductivity, which make them good candidates for supports in sensors. These materials showed an almost linear dependence between the potential and the pH of aqueous solutions.

This work studied the thermochemical treatment of AISI H13 steel used for extrusion of aluminum parts, by plasma ionic nitriding, with the objective of increasing the surface hardness of the mold, by forming an external layer of stable nitrides, increasing the resistance to wear, fatigue, corrosion and thermal resistance. Because it uses ions, plasma ion nitriding is more efficient than liquid and gas nitriding. This process is widely used for ferrous materials and aluminum. The main applications are for extrusion, material injection molds, cutting tools and automotive parts. In this work, samples of the AISI H13 steel were nitrided to be used as aluminum injection molds. The treatment was carried out at 300 oC in a sodium cyanide bath, for a period of 6 h at a pressure of 15 mTorr (2 Pa). The gaseous mixture inside the nitreter consisted of 80% N2 + 20% H2. After treatment, Vickers hardness measurements reached surface values of 963 HV. The results at the end of the treatment showed a 122 µm nitrided layer.

We present the first results about Bragg grating devices in undoped PMMA POF fabricated with relative low cost Nd:YAG laser (when compared with excimer lasers) at 266 nm wavelength at low transmission loss in 850 nm region. Then temperature, humidity and strain characterizations are supplied for potential applications.

In this paper, a network of 37 fiber Bragg grating (FBG) sensors is proposed for real-time, in situ, and operando multipoint monitoring of the surface temperature distribution on a pack of three prismatic lithium polymer batteries (LiPBs). Using the network, a spatial and temporal thermal mapping of all pack interfaces was performed. In each interface, nine strategic locations were monitored by considering a three-by-three matrix, corresponding to the LiPBs top, middle and bottom zones. The batteries were subjected to charge and discharge cycles, where the charge was carried out at 1.0 C, whereas the discharge rates were 0.7 C and 1.4 C. The results show that in general, a thermal gradient is recognized from the top to the bottom, but is less prominent in the end-of-charge steps. The results also indicate the presence of hot spots between two of the three batteries, which were located near the positive tab collector. This occurs due to the higher current density of the lithium ions in this area. The presented FBG sensing network can be used to improve the thermal management of batteries by performing a spatiotemporal thermal mapping, as well as by identifying the zones which are more conducive to the possibility of the existence of hot spots, thereby preventing severe consequences such as thermal runaway and promoting their safety. To our knowledge, this is the first time that a spatial and temporal thermal mapping is reported for this specific application using a network of FBG sensors.

Cardiovascular diseases are the main cause of death in the world and its occurrence is closely related to arterial stiffness. Arterial stiffness is commonly evaluated by analysing the arterial pulse waveform and velocity, with electromechanical pressure transducers, in superficial arteries such as carotid, radial and femoral. In order to ease the acquisition procedure and increase the patients comfort during the measurements, new optical fibre techniques have been explored to be used in the reliable detection of arterial pulse waves, due to their small size, high sensitivity, electrical isolation and immunity to electromagnetic interference. More specifically, fibre Bragg gratings (FBGs) are refractive index modulated structures engraved in the core of an optical fibre, which have a well-defined resonance wavelength that varies with the strain conditions of the medium, known as Bragg wavelength. In this work, FBGs were embedded in a commercial resin, producing films that were used to assess the arterial pulse in superficial locations such as carotid, radial and foot dorsum. The technique proved to be a promising, comfortable and trustworthy way to assess the arterial pulses, with all the optical fibre use advantages, in a non-intrusive biomedical sensing procedure. Examples of possible applications of the developed structures are smart skin structures to monitor arterial cardiovascular parameters, in a stable and reliable way, throughout daily activities or even during exams with high electromagnetic fields, such as magnetic resonance imaging.

There is a set of important selection criteria in the design of fiber optic sensors that determine the compromise between design complexity and performance. Optical fiber sensors not only withstand high temperatures, but they can also operate in different chemical and aqueous media allowing measurements in areas not otherwise accessible. A Fabry-Perot cavity based on an air bubble created in a multimode fiber section is proposed. The air bubble is formed using only cleaving and fusion splicing techniques. The parameters used to produce the microcavities were found empirically. Two different configurations are explored: an inline cavity formed between two sections of MMF, and a fiber tip sensor. In the last, after the air bubble is created, a cleave is made near the cavity, after which the sensor is subjected to several electrical arcs to reshape the cavity and obtain a thin diaphragm. The inline sensor, with a length of ~297 μm, was used to measure strain and presented a sensitivity of 6.48 pm/μe. Regarding the fiber tip sensor, it was subjected to glycerin/water mixture variations, by immerging the sensing head in several solutions with different concentrations of water in glycerin. In this case, the sensor had a length of ~167 μm and a diaphragm thickness of ~20 μm. As expected, with the increase of the external medium refractive index, the sensor visibility decreased. Furthermore, a wavelength shift towards red was observed, with a sensitivity of 7.81 pm/%wt. Both devices exhibited low dependence to temperature (

International audience; The removal of low concentrations of acetic acid from indoor air at museums poses serious preservation problems that the current adsorbents cannot easily address owing to their poor affinity for acetic acid and/or their low adsorption selectivity versus water. In this context, a series of topical water-stable metal-organic frameworks (MOFs) with different pore sizes, topologies, hydrophobic characters, and functional groups was explored through a joint experimental-computational exploration. We demonstrate how a subtle combination of sufficient hydrophobicity and optimized host-guest interactions allows one to overcome the challenge of capturing traces of this very polar volatile organic compound in the presence of humidity. The optimal capture of acetic acid was accomplished with MOFs that do not show polar groups in the inorganic node or have lipophilic but polar (e.g., perfluoro) groups functionalized to the organic linkers, that is, the best candidates from the list of explored MOFs are MIL-140B and UiO-66-2CF3. These two MOFs present the appropriate pore size to favor a high degree of confinement, together with organic spacers that allow an enhancement of the van der Waals interactions with the acetic acid. We establish in this work that MOFs can be a viable solution to this highly challenging problem in cultural heritage protection, which is a new field of application for this type of hybrid materials.

In this work, we study for the first time the influence of microwave power higher than 2.0 kW on bonded hydrogen impurity incorporation (form and content) in nanocrystalline diamond (NCD) films grown in a 5 kW MPCVD reactor. The NCD samples of different thickness ranging from 25 to 205 μm were obtained through a small amount of simultaneous nitrogen and oxygen addition into conventional about 4% methane in hydrogen reactants by keeping the other operating parameters in the same range as that typically used for the growth of large-grained polycrystalline diamond films. Specific hydrogen point defect in the NCD films is analyzed by using Fourier-transform infrared (FTIR) spectroscopy. When the other operating parameters are kept constant (mainly the input gases), with increasing of microwave power from 2.0 to 3.2 kW (the pressure was increased slightly in order to stabilize the plasma ball of the same size), which simultaneously resulting in the rise of substrate temperature more than 100 °C, the growth rate of the NCD films increases one order of magnitude from 0.3 to 3.0 μm/h, while the content of hydrogen impurity trapped in the NCD films during the growth process decreases with power. It has also been found that a new H related infrared absorption peak appears at 2834 cm-1 in the NCD films grown with a small amount of nitrogen and oxygen addition at power higher than 2.0 kW and increases with power higher than 3.0 kW. According to these new experimental results, the role of high microwave power on diamond growth and hydrogen impurity incorporation is discussed based on the standard growth mechanism of CVD diamonds using CH4/H2 gas mixtures. Our current experimental findings shed light into the incorporation mechanism of hydrogen impurity in NCD films grown with a small amount of nitrogen and oxygen addition into methane/hydrogen plasma.

We investigate the impact of methane concentration in hydrogen plasma on the growth of large-grained polycrystalline diamond (PCD) films and its hydrogen impurity incorporation. The diamond samples were produced using high CH4 concentration in H2 plasma and high power up to 4350 W and high pressure (either 105 or 110 Torr) in a microwave plasma chemical vapor deposition (MPCVD) system. The thickness of the free-standing diamond films varies from 165 µm to 430 µm. Scanning electron microscopy (SEM), micro-Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology, crystalline and optical quality of the diamond samples, and bonded hydrogen impurity in the diamond films, respectively. Under the conditions employed here, when methane concentration in the gas phase increases from 3.75% to 7.5%, the growth rate of the PCD films rises from around 3.0 µm/h up to 8.5 µm/h, and the optical active bonded hydrogen impurity content also increases more than one times, especially the two CVD diamond specific H related infrared absorption peaks at 2818 and 2828 cm−1 rise strongly; while the crystalline and optical quality of the MCD films decreases significantly, namely structural defects and non-diamond carbon phase content also increases a lot with increasing of methane concentration. Based on the results, the relationship between methane concentration and diamond growth rate and hydrogen impurity incorporation including the form of bonded infrared active hydrogen impurity in CVD diamonds was analyzed and discussed. The effect of substrate temperature on diamond growth was also briefly discussed. The experimental findings indicate that bonded hydrogen impurity in CVD diamond films mainly comes from methane rather than hydrogen in the gas source, and thus can provide experimental evidence for the theoretical study of the standard methyl species dominated growth mechanism of CVD diamonds grown with methane/hydrogen mixtures.

A network of FBGs was used to monitor temperature and strain variations in LiB in parallel and perpendicular directions. Higher strain variations of (287.35 ± 0.01) µe were obtained by the sensors placed on parallel.

A multimode interferometer based on an etched coreless optical fiber tip is proposed for the determination of the thermo-optic coefficient of ethanol-water mixtures, through refractive index and temperature measurements.

In the last years, optical fiber based sensors and systems for ehealthcare attracted the attention of the scientific community. Over this chapter, optical fiber technology is presented, referring the different types of optical fibers, its main characteristics, and advantages over other sensing methodologies. In addition, optical fiber based sensors and sensing techniques are discussed and several works reported in the literature are reviewed showing that they are a valuable technique to improve healthcare service to the community and as a potential solution to answer different problems. The final section of the chapter consists of the description of three applications of optical sensors in healthcare, namely monitoring of human joint movement, measuring strain of biological tissues, and characterization of medical materials.

A reflective fiber optic sensor based on multimode interference for the measurement of glucose aqueous solutions is proposed. A maximum experimental resolution of 0.04 wt.% of glucose is achieved.

Central arterial pulse pressure monitoring has been considered a key factor in hypertension assessment and cardiovascular prevention. In this paper, it is presented an intensity-based plastic optical fiber sensor for noninvasive monitoring of the carotid pulse waveform. The advantages of this sensing method are the low implementation cost, high robustness, and the signal processing simplicity. The sensor showed a suitable sensitivity to movements up to 370 μm, with a displacement resolution of 0.1 μm. As preliminary proof of concept, the sensor was used to detect the arterial pulse waveform in some human subjects, allowing the assessment of key indexes for heart and arterial stiffness evaluation, such as augmentation index, subendocardial viability ratio, and ejection duration.

Results of the preparation and characterization of graphene oxide–optical fiber coatings will be presented, considering its potential use for sensing applications. The coatings were deposited using the electrostatic self–assembly method, considering different parameters (average sheet size of the graphene oxide colloidal solutions, the number of the deposited layers and the coating methodology) and characterized through SEM and Raman analyses. Aiming to explore this scheme for sensing applications, graphene oxide-coated tilted fiber Bragg gratings were characterized to refractive index variations. An improvement on the sensitivity was obtained and this result suggests that this could be a promising research field for the development of a new line of sensors.

Despite its toxicity, in low concentrations, nitric oxide (NO) is a small endogenous molecule with a particularly important role in the regulation of several biochemical pathways of the human body. The potential of l-histidine-modified clays (organoclays) for storage and therapeutic release of nitric oxide was assessed. Materials were characterized by powder X-ray diffraction, TG-DSC, IR spectroscopy, and nitrogen adsorption at -196 °C. The NO storage and release kinetics was studied both in the gas and liquid phases. For some materials, improvement was observed for both the released amounts and the release profile for the organoclays in relation to the respective raw clays. Assays with HeLa cells indicated that the materials have low cytotoxicity.

A Fabry-Perot air bubble microcavity fabricated between a section of single mode fiber and a multimode fiber is proposed. The study of the microcavities growth with the number of applied arcs is performed. The sensors are tested for lateral load and strain, where sensitivities of 0.32 nm/N and 2.11 nm/N and of 4.49 pm/μe and 9.12 pm/μe are obtained for the 47 μm and 161 μm long cavities, respectively. The way of manufacturing using a standard fusion splicer and given that no oils or etching solutions are involved, emerges as an alternative to the previously developed air bubble based sensors.

We present, for the first time, the results regarding the production of refractive index (RI) sensors, through the acousto-optic effect in tilted fiber Bragg gratings (TFBGs). The RI is analysed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.3327 to 1.4249.

Tilted fiber Bragg gratings (TFBGs) are one of the most attractive kind of optical fiber sensor technology due to their intrinsic properties. On the other hand, the acousto-optic effect is an important, fast and accurate mechanism that can be used to change and control several properties of fiber gratings in silica and polymer optical fiber. Several all-optical devices for optical communications and sensing have been successfully designed and constructed using this effect. In this work, we present the recent results regarding the production of optical sensors, through the acousto-optic effect in TFBGs. The cladding and core modes amplitude of a TFBG can be controlled by means of the power levels from acoustic wave source. Also, the cladding modes of a TFBG can be coupled back to the core mode by launching acoustic waves. Induced bands are created on the left side of the original Bragg wavelength due to phase matching to be satisfied. The refractive index (RI) is analyzed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.33 to 1.43.

Due to their high hemocompatibility and gas permeation capacity, bi-soft segment polyurethane/polycaprolactone (PU/PCL) polymers are promising materials for use in membrane blood oxygenators. In this work, both nonporous symmetric and integral asymmetric PU/PCL membranes were synthesized, and the permeation properties of the atmospheric gases N2, O2, and CO2 through these membranes were experimentally determined using a new custom-built gas permeation apparatus. Permeate pressure vs. time curves were obtained at 37.0 &deg, C and gas feed pressures up to 5 bar. Fluxes, permeances, and permeability coefficients were determined from the steady-state part of the curves, and the diffusion and sorption coefficients were estimated from the analysis of the transient state using the time-lag method. Independent measurements of the sorption coefficients of the three gases were performed, under equilibrium conditions, in order to validate the new setup and procedure. This work shows that the gas sorption in the PU/PCL polymers is the dominant factor for the permeation properties of the atmospheric gases in these membranes.