In this work, we present a novel corrugated long-period grating. The structure was made through the periodic distribution of a photopolymerizable resin onto the surface of an optical fiber, followed by an etching process. The device showed capabilities to be used in strain, displacement, and temperature applications. For the strain measurement, the resonance dip power was linearly increased at a rate of 1.3 dB/mε, showing negligible wavelength shift, making it ideal for lowcost intensity detection schemes. Regarding the displacement characterization, it was verified the capability to measure this parameter in both power and wavelength detection schemes, being the most attractive feature its wide measurement range, i.e. ≈ 25 mm, being above the ones reported in literature. For the temperature, it was verified that there is a direct correlation between the increase of the temperature and the dip wavelength shift.
Plastic Optical Fibers (POFs) are becoming popular for the development of sensors with multiple applications. In this work, we report a preliminary study related with the coating of modified POFs with proteins. Samples of POF were immersed in buffer and in proteins’ solutions under different experimental conditions: modification of the POF sample, immersion time, temperature, buffer solution and concentration of protein. A simple and easy methodology using protein staining solution was performed to confirm the coating of the POFs with proteins and to evaluate the dependency with the experimental conditions. Further developments will be focused on the coating of POFs with modified proteins for the selective detection of contaminants in water contributing to the development of low-cost POF chemical sensors and biosensors.
We report the development of a low cost plastic optical fibre (POF) sensor for ammonium detection using molecularly imprinted polymers (MIP’s). The cladding of a 1 mm diameter PMMA fiber is removed, in which is grafted a molecular imprinted polymer (MIP), by radical polymerization with thermal initiation, that act as a selective sensing layer. For the polymerization, 2,2’-Azobis(2-methylpropionamidine)dihydrochloride (AAPH) is used as initiator, methacrylic acid (MAA) as a monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linker, ammonium chloride (NH4Cl) as a template and 30% of ethanol in water as a solvent. The sensing method consists of an intensity based scheme. The response to different concentrations of ammonium solutions in water has been evaluated at room temperature. Solutions with (0 - 0.6) M concentration, with the corresponding refractive indexes varying between 1.3325 - 1.3387, at 25°C were used. The response of the fiber with the original cladding, and after cladding removal has been monitored and compared to the response given by the developed sensor. The response is very fast, less than 1 minute and reversible, which allows the continuum use of the sensor. Further developments are focused in optimization of MIP grafting procedure and sensor performance, in order to increase sensitivity.
A new approach for data analysis and classification for datasets obtained by a multiparameter optical turbidity sensor is proposed. This approach is based on the combination of statistical or machine learning methods such as linear regressions and clustering analysis. A case study is presented using a 6 dimensional fiber optic sensor to simultaneously classify types of sediments and concentration. Results show a 79% of success for the used training data sets. The methodology proposed is flexible because can be easily adapted to other physical scenarios.
In this paper, we report, to our knowledge, the first demonstration of the induction of long-period and Bragg gratings on surface-core optical fibers. Surface-core fibers described herein were fabricated from commercial silica tubes and germanium-doped silica rods by employing a very simple procedure. Being the core on the fiber surface, it can be sensitive to refractive index variations in the environment in which the fiber is immersed. Thus, results concerning the sensitivity of these gratings to environmental refractive index variations are presented. Besides, simulation data are presented for comparison to the experimental behavior and for projecting future steps in this research.
In this work, the inscription in few seconds of a Bragg grating array in undoped PMMA mPOF using the phase mask technique is reported. The fast growth was possible through the use of a 248 nm UV laser, with suited laser parameters, allowing the creation of a core refractive index modulation without damaging the fiber surface. The Bragg gratings were written in the IR region presenting good spectral properties, achieving for the best case 30 dB reflectivity and 0.2 nm bandwidth. The Bragg grating array was characterized to strain and results are in agreement with the values reported in literature.
Currently, the surface plasmon resonance (SPR) based sensors are mainly focused in visible frequencies, being a barrier for a better integration with the typical fiber optical communication transmission bands. Here, it is presented a theoretical analysis of a SPR based fiber optic sensor with a uniform gold coating on a U-shaped probe. The sensor does not require any fiber etching treatment which eases and improves the control of the overall process. The response of the device to refractive index variations was investigated and a resolution of 10-8 is foreseen for refractive indices around 1.413, becoming the proposed sensor a useful tool for biological and chemical applications.
Madeira wine is a fortified wine produced in Madeira Island, Portugal. Its characteristics are strongly influenced by the winemaking method used which includes a typical and unique step called estufagem. This process consists on heating the wine up to 55 ºC for at least 3 months. In this paper, the characterization of the sensor for the pilot scale facility of estufagem installed in Madeira University is presented, being the device an optimization of a previous version. The response of the sensor was tested towards colour and refractive index, showing a good performance. Madeira wine with different estufagem times was also analysed.
A refractive index and viscosity sensor based on FBGs in mPOF is reported for the first time. The refractive index was measured with a sensitivity of -10:98nm=RIU and a resolution of 1 – 10-4RIU. Viscosity measurements were performed with acousto-optic modulation, obtaining a sensitivity of -94:42%=mPa • s and a resolution of 0:06mPa • s.
The inscription of Bragg gratings in different POFs, including GI-POF is presented. Additionally the cross-sensitivity characterization to temperature and strain for an mPOF FBG is reported for the first time. Results show better sensitivity performances after the annealing process which will help to develop new sensitive optical devices.
In this work, the study of a particular step of Madeira’s winemaking process called estufagem with a plastic optical fibre sensor is presented. Madeira wine is a type of fortified wine produced in the Madeira island of Portugal. The characteristic aroma and exceptional stability of these wines result from the singular used winemaking method that consists in the estufagem where the wine is heated up to 55 °C for at least 3 months, among other steps. This heating based process can produce significant changes in wine colour, aroma and taste. By measuring the transmitted optical power through the wine in three different cells at three different wavelengths it is possible to monitor wine colour evolution during the estufagem. The plastic optical fibres offer easy non-skilled handling, ruggedness and low cost, overcoming the difficulties of the electronic and conventional systems and improving the time of the laboratory offline methods. Results show that it is possible to distinguish the different Madeira wines (from sweet to dry wines) obtained based on different wine grapes as well as the colour evolution during the diverse months of the estufagem.
We report on the production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in two spectral regions using polymer optical fibers (POFs). Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 850 nm and 1550 nm were fabricated in several types of polymer optical fibers. The 3 dB FBG bandwidth varies from 0.22 nm down to 0.045 nm considering a Bragg grating length of 10 mm and 25 mm, respectively.
The present work addresses the need for new devices felt in the context of quality control, especially in the food industry. Due to the spectral dependence of the attenuation coefficient, a novel dual-parameter sensor for colour and refractive index was developed and tested. The sensor employs plastic optical fibres to measure the transmitted optical power in three measurement cells each with a different incident wavelength. The performance of the sensor was tested using several dyes at different concentrations and aqueous solutions of glycerine and ethanol. Results show that this technique allows the monitoring of refractive index and colour without cross-sensitivity.
The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.
The present work addresses the control of the mPOF Bragg grating spectrum properties through acousto-optic
modulation. For the first time, the interaction of a flexural acoustic wave, generated by longitudinal excitation of
different frequencies, with the Bragg grating will be presented. Also it will be demonstrated the quasi linear relationship
between PZT load and maximum reflected power/ 3dB bandwidth of the reflected spectrum.
One of the early predictors of cardiovascular diseases, with growing interest, is the arterial stiffness which is typically
evaluated through the velocity and morphology of the arterial pressure wave.
In each cardiac cycle the heart generates a pressure wave which propagates through the arterial tree. Along its path, the
pressure wave interacts with the arterial walls and, consequently, the morphology of a local arterial pressure wave can be
assessed by the arterial distention movement. Due to its superficiality, proximity of the heart and high probability of
atherosclerosis development, the carotid artery has particular interest to be monitored.
In this work, the development of a non-invasive fibre Bragg grating (FBG) probe for the acquisition of the arterial
distention wave is presented. Comparing to traditional methods, optical FBG based sensors can offer many advantages,
namely, compactness, immunity to electromagnetic interference, high sensitivity, low noise and immunity to light source
intensity due to its codification in the wavelength domain.
The arterial movements induce strain on a uniform FBG, with the arterial distention pattern. The carotid pulse wave was
successful accessed in young human carotid artery, with an acquisition rate of 950 Hz, allowing a clear distinction of the
carotid pulse identification points.
Sensors based on side-polished plastic optical fibre are presented. To enhance the sensitivity to a certain physical
parameter, the guiding properties of an optical fibre have to be weakened. Side-polishing technique offers a simple
implementation, since the mechanical resistance of the POF allows an easy removal of a portion of the jacket, cladding
and core. Three sensors are characterized under a wide range of external refractive indexes. Both, theoretical and
experimental results show that the range of operation of the refractive index sensor can be shifted by using different
geometries or different macrobending conditions of the sensitive area. The phenomenon behind the principle of operation
of the sensor is the reflection and transmission of light at an interface of two dielectric media expressed by Fresnel's
equations. The use of this intrinsic scheme to monitor the cure process of a material or the viscosity of a liquid is also
presented. The changes in refractive index are used to monitor, in real time, the cure of different materials such as resins
and varnishes because the optical properties of the material can be related to the density of the material. The viscosity of
a liquid is related to the droplet formation in a convexly bended sensor.
The present work addresses the need for low-cost turbidity sensors felt in the context of an ongoing research project on
enhanced soil erosion following wildfire in Portugal. To this end, a system based on plastic optical fibre was developed
and tested, including against a commercially-available system. The performance of the sensor was tested using
artificially-created samples with a wide range of concentration of three types of very distinct materials, six particle size
classes of ashes and real runoff samples collected at the slope and catchment scale in a recently burned area.
Three optical monitoring joint angle devices with the ability of real-time assessment of the knee, elbow and ankle
movements are presented. All devices were tested in different selected tasks and its performance evaluated. Results have
shown that these side-polished plastic optical fiber based systems are a valid technique and suitable to aid physicians in
the diagnosis and rehabilitation of joint injuries, to monitor the performance of high competition athletes or even to
quantify daily activities. The wearable sensor systems have properties such as low-cost, friendly operation and less effect
to human which are important topics in biomechanics and clinical applications.
The characterization of fiber Bragg grating (FBG) sensors integrated on 2D and 3D mesh structures is presented. Several
materials and configurations were tested, namely cork, foams, PVC, hexagonal 3D. Sensors were embedded between two
substrates using textile lamination technique. Every sample was subjected to temperature variations and mechanical
deformations. Through Bragg wavelength monitoring, thermal, deformation and pressure performance were evaluated.
These results provide significant information to the conception of smart textiles.
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