Efficient large-scale multiplexing of fiber Bragg grating and fiber Fabry-Perot sensors for structural health monitoring applications

Fiber Bragg gratings have been demonstrated as a versatile sensor for structural health monitoring. We present an efficient and cost effective multiplexing method for fiber Bragg grating and fiber Fabry-Perot sensors based on a broadband mode-locked fiber laser source and interferometric interrogation. The broadband, pulsed laser source permits time and wavelength division multiplexing to be employed to achieve very high sensor counts. Interferometric interrogation also permits high strain resolutions over large frequency ranges to be achieved. The proposed system has the capability to interrogate several hundred fiber Bragg gratings or fiber Fabry-Perot sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. Strain resolutions of 30n epsilon/Hz(1/2) and 2 n epsilon/Hz(1/2) are demonstrated with the fiber Bragg grating and fiber Fabry-Perot sensor respectively. The fiber Fabry-Perot sensor provides an increase in the strain resolution over the fiber Bragg grating sensor of greater than a factor of 10. The fiber Bragg gratings are low reflectivity and could be fabricated during the fiber draw process providing a cost effective method for array fabrication. This system would find applications in several health monitoring applications where large sensor counts are necessary, in particular acoustic emission

Novel Microfiber Sensor and Its Biosensing Application for Detection of hCG Based on a Singlemode-Tapered Hollow Core-Singlemode Fiber Structure

A novel microfiber sensor is proposed and demonstrated based on a singlemode-tapered hollow core -singlemode (STHS) fiber structure. Experimentally a STHS with taper waist diameter of 26.5 μm has been fabricated and RI sensitivity of 816, 1601.86, and 4775.5 nm/RIU has been achieved with RI ranges from 1.3335 to 1.3395 , from 1.369 to 1.378, and from 1.409 to 1.4175 respectively, which agrees very well with simulated RI sensitivity of 885, 1517, and 4540 nm/RIU at RI ranges from 1.3335 to 1.337, from 1.37 to 1.374, and from 1.41 to 1.414 . The taper waist diameter has impact on both temperature and strain sensitivity of the sensor structure: (1) the smaller the waist diameter, the higher the temperature sensitivity, and experimentally 26.82 pm/°C has been achieved with a taper waist diameter of 21.4 μm; (2) as waist diameter decrease, strain sensitivity increase and 7.62 pm/με has been achieved with a taper diameter of 20.3 μm. The developed sensor was then functionalized for human chorionic gonadotropin (hCG) detection as an example for biosensing application. Experimentally for hCG concentration of 5 mIU/ml, the sensor has 0.5 nm wavelength shift, equivalent to limit of detection (LOD) of 0.6 mIU/ml by defining 3 times of the wavelength variation (0.06 nm) as measurement limit. The biosensor demonstrated relatively good reproducibility and specificity, which has potential for real medical diagnostics and other applications

Desenvolvimento de sensores óticos de pH para aplicação em aquacultura e integração em plataforma híbrida multi-parâmetro

Optical fiber sensors have shown a lot of potential for application in marine environments e regarding monitoring multiple parameters crucial to the growth and well-being of fish, of which pH is one of the most important. Regarding this work, two types of optical fiber sensors were produced: tapers made from a silica single mode fiber with a fiber Bragg grating, and D-shape plastic optical fibers. There were used two different types of D-shape plastic optical fibers: home-made, using a polishing machine, and reused, from old cortisol sensors. Polyaniline (PANI) was synthesized by oxidative polymerization of aniline that was carried out onto the fibers and the selected synthesis time, for which better results were obtained, was 20 minutes. The sensitivity and the sensors’ behavior are determined by the geometry modifications applied onto the fibers, which allow the access of the evanescent wave to the surrounding medium which, in combination with polyaniline, results in a transmission decrease of the spectra as pH increases. The sensors present a certain degree of reproducibility and repeatability with the tapers, the D-shapes home-made and reused having a sensitivity of –0.25 dB/pH, –500 counts/pH and –2500 counts/pH, respectively. However, this is only valid for the increasing order. Regarding the stabilization time, for extreme pH values, whether very acidic, totally protonated, or very basic, totally unprotonated, the stabilization time is shorter. On the other hand, for the transition values of pH, this time is longer, since the PANI is in a transition phase. There were also made cross-sensitivity tests related to ionic strength and temperature, where the sensors did not show a spectra variation in the range of interest. Additionally, the pH sensor was integrated in a hybrid platform with a sensor of nitrites and the optical response to the increment of nitrites in a PBS solution was observed, having only slight variations. The tapers are very useful due to their remote sensing and multiplexing, which is the reason they were spliced with a sensor of nitrites. However, these lack mechanical robustness and ease of fabrication. On the other hand, the opposite happens in the D-shapes. These are more robust and easier to manufacture, but the possibility of multiplexing or remote sensing is challenging or unknown. As a future work, it is intended that the pH sensors produced are applied directly on the aquaculture tanks in order to identify possible water interferences in the measurements and perform tests to optimize the hybrid structure.Os sensores em fibra ótica têm-se mostrado muito promissores para a aplicação em ambientes marinhos na monitorização de vários parâmetros cruciais ao bom crescimento e reprodução dos peixes, dos quais o pH é dos mais importantes no setor da aquacultura. No caso deste trabalho, dois tipos de sensores em fibra ótica foram produzidos: tapers feitos a partir de uma fibra de sílica monomodo com uma rede de Bragg e fibras óticas de plástico com uma D-shape. Em relação às fibras óticas de plástico D-shape, foram usados dois tipo diferentes: umas produzidas no laboratório, usando uma máquina de polir, e outras foram reutilizadas a partir de sensores antigos de cortisol. A polianilina (PANI) foi sintetizada por polimerização oxidativa da anilina na presença das fibras e o tempo de síntese escolhido, para o qual se obteve melhores resultados, foi 20 minutos. A sensibilidade e comportamento do sensor são determinados pelas modificações de geometria aplicadas nas fibras que permitem que a onda evanescente tenha acesso ao meio circundante e, em combinação com a polianilina, isto resulta numa diminuição da transmissão dos espetros à medida que o pH aumenta. Os sensores apresentam um certo grau de reprodutibilidade e repetibilidade, com os tapers, as fibras D-shape produzidas no laboratório e as reutilizadas com sensibilidade de –0.25 dB/pH, –500 contagens/pH e –2500 contagens/pH, respetivamente. Contudo, isto apenas é válido no sentido ascendente de pH. Relativamente ao tempo de estabilização, para os extremos das regiões de pH, quer seja muito ácido, totalmente protonado, ou muito básico, totalmente desprotonado, o tempo de estabilização é mais curto. Já para os valores de transição de pH este tempo é mais elevado, pois a PANI também está numa fase de transição. Foram ainda efetuados testes de sensibilidade cruzada no que diz respeito à força iónica e à temperatura, sendo que os sensores não mostraram uma alteração espetral na zona de interesse. Adicionalmente, integrou-se o sensor de pH numa plataforma híbrida com um sensor de nitritos e observou-se a resposta ótica ao adicionar nitritos a uma solução de PBS, o que resultou em variações pouco significativas. As fibras tapers são bastante úteis devido às suas capacidades de monitorização remota e multiplexagem, daí terem sido fundidos com um sensor de nitritos. No entanto, estes carecem de robustez mecânica e facilidade de fabrico. Por outro lado, nas fibras D-shape o oposto é observado. Estas são mais robustas mecanicamente e fáceis de fabricar, mas a possibilidade de multiplexar ou monitorizar remotamente é desconhecida ou mais complicada. Como trabalho futuro pretende-se que os sensores de pH produzidos sejam aplicados diretamente nos tanques de aquacultura a fim de identificar possíveis interferentes da água nas medidas e de realizar testes para otimizar a estrutura híbrida.Mestrado em Engenharia Físic

Optical fiber relative humidity sensor based on a FBG with a di-ureasil coating

In this work we proposed a relative humidity (RH) sensor based on a Bragg grating written in an optical fiber, associated with a coating of organo-silica hybrid material prepared by the sol-gel method. The organo-silica-based coating has a strong adhesion to the optical fiber and its expansion is reversibly affected by the change in the RH values (15.0–95.0%) of the surrounding environment, allowing an increased sensitivity (22.2 pm/%RH) and durability due to the presence of a siliceous-based inorganic component. The developed sensor was tested in a real structure health monitoring essay, in which the RH inside two concrete blocks with different porosity values was measured over 1 year. The results demonstrated the potential of the proposed optical sensor in the monitoring of civil engineering structures

Microstructured Optical Fiber Sensors Embedded in a Laminate Composite for Smart Material Applications

Fiber Bragg gratings written in highly birefringent microstructured optical fiber with a dedicated design are embedded in a composite fiber-reinforced polymer. The Bragg peak wavelength shifts are measured under controlled axial and transversal strain and during thermal cycling of the composite sample. We obtain a sensitivity to transversal strain that exceeds values reported earlier in literature by one order of magnitude. Our results evidence the relevance of using microstructured optical fibers for structural integrity monitoring of composite material structures

Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra

The spectral characteristics of a fiber Bragg grating (FBG) with a transversely inhomogeneous refractive index profile, differs con- siderably from that of a transversely uniform one. Transmission spectra of inhomogeneous and asymmetric FBGs that have been inscribed with focused ultrashort pulses with the so-called point-by-point technique are investigated. The cladding mode resonances of such FBGs can span a full octave in the spectrum and are very pronounced (deeper than 20dB). Using a coupled-mode approach, we compute the strength of resonant coupling and find that coupling into cladding modes of higher azimuthal order is very sensitive to the position of the modification in the core. Exploiting these properties allows precise control of such reflections and may lead to many new sensing applications.Comment: Submission to OE, 16 pages, 6 figure

Ultrafast Optical Signal Processing with Bragg Structures

The phase, amplitude, speed, and polarization, in addition to many other properties of light, can be modulated by photonic Bragg structures. In conjunction with nonlinearity and quantum effects, a variety of ensuing micro- or nano-photonic applications can be realized. This paper reviews various optical phenomena in several exemplary 1D Bragg gratings. Important examples are resonantly absorbing photonic structures, chirped Bragg grating, and cholesteric liquid crystals; their unique operation capabilities and key issues are considered in detail. These Bragg structures are expected to be used in wide-spread applications involving light field modulations, especially in the rapidly advancing field of ultrafast optical signal processing.Comment: To be published in a special issue of journal Applied Sciences, on the topic of Guided-Wave Optic

Optical sensors for cultural heritage and biomedical applications

The current Ph.D. thesis is articulated in 4 different research paths. The main research topic is on the fiber Bragg grating (FBG) sensor and its applications, mainly related to the conservation of the original status of the artworks. The second topic is related to the development of a new methodology for measuring the cracking of the Structural Health Monitoring (SHM) of cultural heritage. In the third topic, it is addressed the subject on the complex diatribe related to the risk in delivering anesthesia; field in which I have been also working, being a Biomedical Engineer. Finally, in the last topic it is proposed a biomechanics study on the patellar taping with the purpose of finding a correlation between the taping and a neuromuscular response. A new era of pollution requires an important focus on the conservation of archaeological sites and monuments. In the last years, great efforts were made to develop various sensors for different tasks; the FBG was one of the most studied thanks to the multitude of applications and the surprising performances. An original fiber optic sensor that combines the fiber Bragg gratings with a pH responsive polymer coating for monitoring the pH of the rains on critical and prestigious monuments is proposed. In this study, the arrangement setup of the optical sensor is modeled with Comsol Multiphysics (Wave Optics Module), based on the FEM (Finite Element Method) solver. Monitoring the pH of the rain can be used by experts to predict and control the corrosion of specific materials, especially limestone and marble, thus scheduling timely restoration. This also depends on the materials under analysis and it can have an important impact in terms of cost reductions and higher maintenance efficiency. In conclusion, the swelling response of hydrogels to the change of surrounding pH allowed the development of a model of hydrogel coated FBG pH sensor. Modelling the FBG pH sensor for monitoring the rain in archaeology and in cultural heritage provided innovative results in terms of high sensitivity and small dimensions of the device, allowing better intervention planning. In the first chapter, a preliminary study regarding the optical ring resonator is conducted because, ultimately, the goal is to realize a sensor that combines the FBG and the ring resonator for future developments in order to improve the sensor performances. Along with the development of the FBG sensor, a new methodology for measuring the cracking for the Structural Health Monitoring (SHM) of cultural heritage is also studied. The methodology is characterized by being minimally invasive on the artefact that has to be preserved, which is one of the main qualities required in this field. The approach is to determine the relative distance between two optical tags, using advanced fitting algorithms for the objective function. Different kinds of objective-function were taken into account in order to identify the best configuration to determine the fitting parameters, useful to the SHM. The optical tags are introduced for this scope; they are nothing but adhesive labels with appropriate images, through which, by using advanced fitting methods and algorithms, it is possible to determine the absolute and relative position and three-dimensional rotations of the images. The third chapter of this thesis deals with the risk and perception of risk in delivering anesthesia. The study examines the different perceptions of risk associated with anesthesia systems from the viewpoints of the product manufacturer and the caregiver. Only little research has been done on the impact of the perception of risk for patient safety in anesthesia. The role of the manufacturer in mitigating the perception of risk is central in the work. The risk was examined as the probability of negative occurrences based on the Medical Device Reportable (MDR) events and these risks were compared to how the caregiver perceives and manages them when delivering anesthesia. Analysis of the manufacturer’s public Medical Device Reportable (MDR) events data was performed in the US market and it represents the actual risk achieved; the bibliographic review provided a perspective on how the risk is perceived and managed by the caregiver when delivering anesthesia. The goal of the research path is to highlight how the role of the manufacturers can have an impact on the reduction of perception of risk in anesthesia, increasing patient safety. Finally, a biomechanical proposal on the estimation of Centre of Mass (CoM) trajectory has been developed. Motion capture systems and force platforms are still considered the gold standard for the estimation of accurate CoM measurements. In the last decade, several methods based on inertial sensors systems have been proposed based on double integration of acceleration signals of pelvis-worn sensors (M. J. Floor-Westerdijk, 2012). Although the portability of those methodologies is higher, drift errors due to extremely lengthy time acquisitions affect measurements, limiting their use. For the purpose of avoiding drift error and providing an accurate tool for ambulatory and/or home CoM assessment, the accuracy of a novel method based on a Biomechanical Model (BM) will be investigated. Among the large number of potential applications, this novel approach could be used in the identification of the effects of the patellar taping on neuromuscular control. More specifically, the patellar taping technique proposed by McConnell (J. McCONNELL, 1986) allows patients to engage in pain-free physical therapy exercises, by medializing the patella. Although this technique has been demonstrated to reduce the perceived pain of patients with patellofemoral pain syndrome and improve neuromuscular activity (N. Aminaka and P. A. Gribble, 2008), a deeper investigation on how patellar tape influences postural stability thought CoM assessment could be of great interest in the long term management of Chondromalacia Patellae. It has been demonstrated, in fact, that patellar taping affects knee proprioception other than relieving pain in subjects with patellofemoral pain syndrome (M. J. Callaghan, 2008). The aim of this research program is to pursue through static and dynamic tasks performed twice both by healthy subjects and not-healthy ones, with and without patellar tape