Real-time absorbance monitoring of layer-by-layer coating process of optical fiber pH sensor

Fiber optical cable was initially used as waveguides to transmit data over long distances. Various sensor applications can be developed using optical fiber by coating it with different coating materials. Layer-by-layer (LbL) technique is utilized in this research in order to introduce coating layers on sensing region. The utilization of this technique enables the production of scalable ultra-thin film using various materials especially polyelectrolyte. Although various studies had been performed using LbL technique, there still a need to monitor the LbL coating process for optimization of the sensor performance. This is because the performance depends on the coating properties including the thickness of the coat. The main objectives of this research were LbL coating system development, determining the optimal number of bilayers coating on the sensing region and evaluation of fabricated fiber sensor performance. The LbL coating system was developed using power supply, Arduino Uno, stepper motors, breadboard, drivers and laser engraver axis. LbL coating process on optical fiber was monitored in real-time using a white light source and a spectrometer. Multiple layers of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were coated to create pH-sensitive coating on the surface of the optical fiber core. Real-time monitoring of the absorbance spectrum during the coating process was conducted from 0 to 50 PAH/PAA bilayers. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) were used to verify the existence of the fiber coating. The results of EDX proved that the PAH and PAA were coated on the fiber. The monitoring spectrum showed that the absorbance value was increased with the increment of PAH/PAA bilayers up to 30 bilayers and started to decrease as the bilayers exceed that value. The results showed that 30 bilayers of PAH/PAA coatings is the optimum number of bilayers coating for pH sensing due to its high absorbance of 0.87 Optical Density (OD) at 800 nm. The pH sensing performance of fiber without PAH/PAA coating and with 5, 10, 15, 20, 30 and 40 bilayers of PAH/PAA coating were compared by immersing the fiber in pH buffer solutions. The performance was determined through the sensitivity, linearity and repeatability of the sensor. 10 PAH/PAA bilayers coated fiber sensor was 120 times more sensitive than the fiber without coating. This shows that the PAH/PAA coating is highly sensitive to pH as compared with uncoated fiber. The best performance was achieved by 30 bilayers of PAH/PAA coated fiber with a sensitivity of 0.453 OD/pH, linearity of 0.959 and standard deviation value below 4%. Numerous physical, chemical and biological sensors can be produced by utilizing the developed LbL coating system in future

(INVITED)Chemical sensors based on long period fiber gratings: A review

Fiber optic devices are being increasingly employed in the fields of chemical and environmental sensing due to their important features, such as high accuracy, small size, chemical inertness, remote operation and multiplexing capabilities. In this work, a thorough review about the design, fabrication and characterization of fiber optic chemical sensors based on long period grating (LPG) technology is reported. The emphasis is placed on transducer designs and features as well as the techniques to enhance the sensitivity. Subsequently, coating materials to be deposited around the grating region, providing a selective response to the target analytes are described in detail. Finally, the different applications are reviewed, mainly related to the monitoring of environmental parameters, volatile organic compounds, hazardous gases, heavy metal ions, corrosion, marine salinity and food quality. The aim of this work is to deliver a comprehensive analysis regarding the state-of-the-art solutions about LPG-based chemical sensors and to summarize the current shortcomings and upcoming research paths

Desarrollo de sensores con cavidad láser de fibra óptica

En este trabajo de fin de grado se presenta una estructura sensora, en base a la unión de un láser de cavidad en anillo y un sensor interferométrico. Mediante diferentes dispositivos software y hardware se ha conseguido estudiar la estabilidad en potencia de la configuración láser en anillo a diferentes cambios de temperatura. La estructura láser utiliza una fibra de erbio que genera un pico a 1550nm a la que se le acopla dos tipos de sensores diferentes. En primer lugar, se realizaron pruebas con una estructura SMS analizando sus cambios frente a índices de refracción. Por otro lado, se ha estudiado el comportamiento de otro sensor basado en fibra hueca, el que fue sometido a variaciones de temperatura. Como resultado, este último ha permitido obtener valores de sensibilidad de hasta 30 nm/oC, lo cual se considera valores muy altos comparados con otros tipos de sensores. Esta estructura basada en fibra hueca es una estructura muy versátil que permite además de la medición de temperatura, medir coeficientes de dilatación de metales, tensiones, vibraciones, etc. por otro lado, gracias a la alta amplificación de la cavidad láser y a su configuración, se podría conseguir una multiplexación de múltiples sensores.Graduado o Graduada en Ingeniería en Tecnologías de Telecomunicación por la Universidad Pública de NavarraTelekomunikazio Teknologien Ingeniaritzako Graduatua Nafarroako Unibertsitate Publikoa

Sol-Gel Coating Membranes for Optical Fiber Sensors for Concrete Structures Monitoring

The use of advanced sensing devices for concrete and reinforced concrete structures (RCS) is considered a rational approach for the assessment of repair options and scheduling of inspection and maintenance strategies. The immediate benefits are cost reduction and a reliable prevention of unpredictable events. The use of optical fiber sensors (OFS) for such purposes has increased considerably in the last few years due to their intrinsic advantages. In most of the OFS, the chemical transducer consists of immobilized chemical reagents placed in the sensing region of the optical sensor by direct deposition or by encapsulation in a polymeric matrix. The choice of the support matrix impacts directly on the performance of the OFS. In the last two decades, the development of OFS functionalized with organic-inorganic hybrid (OIH) sol-gel membranes have been reported. Sol-gel route is considered a simple method that offers several advantages when compared to traditional synthesis processes, allowing to obtain versatile materials with unique chemical and physical properties, and is particularly valuable in the design of OIH materials. This review will provide an update of the current state-of-the-art of the OFS based on OIH sol-gel materials for concrete and RCS since 2016 until mid-2021. The main achievements in the synthesis of OIH membranes for deposition on OFS will be discussed. The challenges and future directions in this field will also be considered, as well as the main limitations of OFS for RCS monitoring. (c) 2021 by the authors. Licensee MDPI, Basel, Switzerland

Sensores de fibra ótica para meios desafiantes

With the present work, the development of fiber optic sensor solutions for the application in challenging media was intended. New sensor structures based on the post-processing of optical fibers were addressed, taking into account their sensitivity to variations in the external environment. In a first stage, fiber Bragg gratings were embedded in lithium batteries, to monitor temperature in situ and operando. Due to the harsh chemical environment of the battery, fiber optic sensors revealed to be the most advantageous alternative, when comparing to the electronic sensors. Fiber sensors exhibited good sensitivities and fast responses, besides being less invasive, thus they did not compromise the battery response. Furthermore, they were chemically stable. Still in the framework of this theme, and with the objective of monitoring possible strain and pressure variations inside the batteries, new sensors based on in-line Fabry-Perot cavities have been proposed. These sensors were characterized in lateral load, strain, and temperature. In a later stage, the study focused on the development of configurations that allowed to obtain high-resolution and/or sensitivity sensors. One of such configurations was obtained by creating a hollow microsphere at the fiber tip. The sensor was used to detected concentration variations and refractive index of glycerin and water mixtures. The influence of the diaphragm size in the sensor response was also studied, as well as the temperature response. New sensors based on multimode interference have also been characterized, using a coreless silica fiber tip. First, the influence of different parameters, such as length and diameters were analyzed. The sensors were tested in different solutions of glucose and water. It was observed that the sensor diameter is a decisive factor in obtaining devices that are more sensitive to refractive index and, consequently, to concentration. The determination of the thermo-optic coefficient of water/ethanol mixtures was also addressed using a multimode fiber interferometer sensor. Finally, a multimode interferometer sensor was functionalized by depositing agarose throughout the structure, allowing to optimize the response of the sensors to the external environment.Com o presente trabalho pretendeu-se explorar soluções de sensores em fibra ótica para a aplicação em meios desafiantes. Novas estruturas sensoras baseadas em pós-processamento de fibra ótica foram abordadas, tendo em consideração a sua sensibilidade a variações do meio externo. Numa primeira etapa, foram embebidas redes de Bragg no interior de baterias de lítio, para monitorizar variações de temperatura in situ e operando. Devido ao complexo meio químico da bateria, os sensores em fibra ótica revelaram ser uma alternativa mais vantajosa em relação aos sensores elétricos, não só pela sensibilidade e rápida resposta, mas também pelo fato de não afetarem o desempenho da bateria. Além disso, os sensores usados revelaram ser pouco invasivos e quimicamente estáveis. Ainda no âmbito deste tema, e com o objetivo de monitorizar possíveis deformações e variações de pressão no interior da bateria de lítio, foram desenvolvidos novos sensores baseados em cavidades de Fabry-Perot do tipo in-line. Esses sensores foram caraterizados em pressão lateral, deformação e temperatura. Numa fase posterior, o estudo centrou-se no desenvolvimento de configurações que permitissem a obtenção de sensores com elevada resolução e/ou sensibilidade. Uma das configurações consistiu na formação de uma microesfera oca na ponta de uma fibra ótica. Esse sensor foi utilizado para detetar variações de concentração e índice de refração de misturas de glicerina e água. A influência do tamanho do diafragma na resposta do sensor também foi estudada, assim como a resposta em temperatura. Em seguida, desenvolveram-se novos sensores baseados em interferência multimodo, utilizando para tal uma ponta de fibra de sílica sem núcleo. Numa primeira abordagem analisou-se a influência de diferentes parâmetros, como o comprimento e o diâmetro dos sensores. Os sensores foram expostos a diferentes soluções de glucose e água. Verificou-se que o diâmetro do sensor é um fator decisivo para a obtenção de dispositivos mais sensíveis ao índice de refração e, consequentemente, à concentração. Foi também desenvolvido um sensor baseado em interferência multimodo que permitiu determinar o coeficiente termo-ótico de misturas de etanol e água. Por fim, procedeu-se à funcionalização de um sensor baseado em interferência multimodo através da deposição de agarose ao longo da estrutura, permitindo assim otimizar a sua resposta a variações do meio externo.Programa Doutoral em Engenharia Físic

Contribución al desarrollo de sensores basados en resonancias de modos con pérdidas en configuración de guía en onda plana

En este trabajo de tesis se muestra el estudio y diseño de sensores basados en el fenómeno de la resonancia de modos con pérdidas en configuración de guía de onda plana, lo que supone un complemento para la plataforma habitual, la fibra óptica. Sus ventajas son la simplicidad de manejo y la robustez de los dispositivos desarrollados. En este sentido, se ha diseñado, sobre la base de la deposición de óxido de cobre (CuO) como material generador de la resonancia, sensores de humedad y de respiración, y sobre la base de la deposición de óxido de tungsteno (WO3), sensores de índice de refracción y de compuestos orgánicos como el etanol, el metanol y la acetona.This thesis work shows the study and design of sensors based on the phenomenon of lossy mode resonance in a planar waveguide configuration, which is a complement to the usual platform, optical fiber. Its advantages are the simplicity of use and the robustness of the devices developed. In this sense, it has been designed, based on the deposition of copper oxide (CuO) as a resonance generating material, humidity and respiration sensors, and based on the deposition of tungsten oxide (WO3), sensors for refractive index and organic compounds such as ethanol, methanol and acetone.Fondo de investigación PID2019-106231RB-I00 de la Agencia Estatal de Investigación española (AEI). Beca de investigación predoctoral de la Universidad Pública de Navarra.Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011)Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011