Maria Fátima Domingues

Detection of Fiber Fuse Effect Using FBG Sensors

In this paper, we propose a new technique to detect the presence of the fiber fuse effect propagation. The implemented technique consists on the utilization of two fiber Bragg gratings (FBGs) as temperature sensors in order to detect the transit of the thermal wave associated with the fuse effect. The developed technique was used to determine the fuse propagation velocity in single mode fibers as function of the injected optical pump power, yielding a direct proportionality constant value of 0.106 ± 0.028 ms-1W-1.

Liquid Hydrostatic Pressure Optical Sensor Based on Micro-Cavity Produced by the Catastrophic Fuse Effect

We propose an optical fiber hydrostatic pressure sensor based on micro-cavities generated by the fiber fuse effect. The presented sensor is manufactured through the recycling of optical fiber destroyed by the fiber fuse effect, being, therefore, a cost-effective solution, when compared with other similar micro-cavity-based solutions. The developed sensor was characterized for pressures up to 20 kPa, showing a linear sensitivity coefficient of 0.47 ± 0.03 nm · kPa-1, for pressure values below 8 kPa. Furthermore, we propose a new theoretical model to describe the behavior of the microcavities embedded in optical fibers. This allows us to solve the discrepancies, already identified by other authors, between the experimental results and the ones attained with the flat mirrors Fabry-Perot model. By this way, we were able to describe the sensor response, within the full dynamic range.

Insole optical fiber Bragg grating sensors network for dynamic vertical force monitoring

Abstract. In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06  pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).

POFBG-Embedded Cork Insole for Plantar Pressure Monitoring

We propose a novel polymer optical fiber (POF) sensing system based on fiber Bragg gratings (FBGs) to measure foot plantar pressure. The plantar pressure signals are detected by five FBGs, in the same piece of cyclic transparent optical polymer (CYTOP) fiber, which are embedded in a cork insole for the dynamic monitoring of gait. The calibration and measurements performed with the suggested system are presented, and the results obtained demonstrate the accuracy and reliability of the sensing platform to monitor the foot plantar pressure distribution during gait motion and the application of pressure. This architecture does not compromise the patient’s mobility nor interfere in their daily activities. The results using the CYTOP fiber showed a very good response when compared with solutions using silica optical fibers, resulting in a sensitivity almost twice as high, with excellent repeatability and ease of handling. The advantages of POF (e.g., high flexibility and robustness) proved that this is a viable solution for this type of application, since POF’s high fracture toughness enables its application in monitoring patients with higher body mass compared with similar systems based on silica fiber. This study has demonstrated the viability of the proposed system based on POF technology as a useful alternative for plantar pressure detection systems.

Phase-Shifted Bragg Grating Inscription in PMMA Microstructured POF Using 248-nm UV Radiation

In this work, we experimentally validate and characterize the first phase-shifted polymer optical fiber Bragg gratings (PS-POFBGs) produced using a single pulse from a 248-nm krypton fluoride laser. A single-mode poly (methyl methacrylate) optical fiber with a core doped with benzyl dimethyl ketal for photosensitivity improvement was used. A uniform phase mask customized for 850-nm grating inscription was used to inscribe these Bragg structures. The phase shift defect was created directly during the grating inscription process by placing a narrow blocking aperture in the center of the UV beam. The produced high-quality Bragg grating structures, presenting a double dips, reject 16.3 dB (97.6% reflectivity) and 13.2 dB (95.2% reflectivity) of the transmitted power, being therefore appropriate for sensing or other photonic applications. Its transmission spectrum possesses two sharp transmission notches, allowing a significant increase in measurement resolution compared to direct interrogation of a single grating. The reflection and transmission spectra when multiple phase shifts are introduced in the fiber Bragg grating structure are also shown. The PS-POFBGs strain, temperature, pressure, and humidity characteristics have been experimentally analyzed in detail to assess their potential usage as sensors.

Low-Cost Interrogation Technique for Dynamic Measurements with FBG-Based Devices

Fiber Bragg gratings are widely used optical fiber sensors for measuring temperature and/or mechanical strain. Nevertheless, the high cost of the interrogation systems is the most important drawback for their large commercial application. In this work, an in-line Fabry–Perot interferometer based edge filter is explored in the interrogation of fiber Bragg grating dynamic measurements up to 5 kHz. Two devices an accelerometer and an arterial pulse wave probe were interrogated with the developed approach and the results were compared with a commercial interrogation monitor. The data obtained with the edge filter are in agreement with the commercial device, with a maximum RMSE of 0.05 being able to meet the requirements of the measurements. Resolutions of 3.6 pm and 2.4 pm were obtained, using the optical accelerometer and the arterial pulse wave probe, respectively.

Optical Fiber Sensors in IoT

Having paved the way, this chapter discusses the use of OFSs in IoT. The current chapter introduces the concept of IoT, highlighting the factors and motivation pushing towards a more connected world; hence the so-called Internet of Things (IoT) and in the more extreme scenario the Internet of Everything (IoE). To begin, the term “Internet of Things” is explained in the first subsection, emphasizing the need for such concept, highlighting the enablers of IoT and their added value. The chapter then moves forward to highlight how OFSs can be integrated in IoT applications, to provide a more added value at lower costs. After a brief introduction of IoT, each subsection tackles a different category of IoT applications, where OFSs are seen to play a role in the very near future. It is worth mentioning here that the current chapter is not intended to provide a complete view of IoT and should not be treated as one. The chapter is alternatively dedicated towards discussing the use of OFSs within IoT.

Principles of Optical Fiber Sensing

Since the Nobel Prize award in 2009, received by Prof. Charles K. Kao, for his research and pioneering achievements regarding the transmission of light in an optical fiber, optical fiber has been regarded as one of the top inventions of the last decades revolutionizing not only telecommunications systems, but also new fields of applications such as sensing and metrology. This chapter provides an introduction to the topic of optical fiber sensing. It starts with defining optical fibers in general, giving guide to how to use them in the field of communications, then moving towards the field of optical fiber sensing. The concept of sensing using optical fibers is introduced. The different types of optical fiber sensing are discussed. In principal, different modulation/demodulation principles can be used for sensing multiple external physical parameter. According to those different principles, several techniques emerged for the production of OFSs. The chapter presents a guide for introducing the different modulation types; hence the categorization of optical fiber sensing.

Foot Plantar Pressure Monitoring with CYTOP Bragg Gratings Sensing System

In this paper, a polymer optical fiber (POF) sensing solution to monitor the pressure induced in the foot plantar surface is investigated. The paper shows the design and implementation of a platform with an array of 5 polymer optical fiber Bragg gratings (POFBGs) placed in key points to monitor the pressure on the foot surface during gait cycles and the body center mass displacements. The results showed a great response compared with solutions using silica optical fibers. A much high sensitivity and repeatability were achieved using the CYTOP fiber as well as proving that the advantages of POF is a viable and useful solution for this type of application for a future implementation of an integrated “in-shoe” CYTOP POFBGs sensor network.

Gait Shear and Plantar Pressure Monitoring: A Non-Invasive OFS Based Solution for e-Health Architectures

In an era of unprecedented progress in sensing technology and communication, health services are now able to closely monitor patients and elderly citizens without jeopardizing their daily routines through health applications on their mobile devices in what is known as e-Health. Within this field, we propose an optical fiber sensor (OFS) based system for the simultaneous monitoring of shear and plantar pressure during gait movement. These parameters are considered to be two key factors in gait analysis that can help in the early diagnosis of multiple anomalies, such as diabetic foot ulcerations or in physical rehabilitation scenarios. The proposed solution is a biaxial OFS based on two in-line fiber Bragg gratings (FBGs), which were inscribed in the same optical fiber and placed individually in two adjacent cavities, forming a small sensing cell. Such design presents a more compact and resilient solution with higher accuracy when compared to the existing electronic systems. The implementation of the proposed elements into an insole is also described, showcasing the compactness of the sensing cells, which can easily be integrated into a non-invasive mobile e-Health solution for continuous remote gait monitoring of patients and elder citizens. The reported results show that the proposed system outperforms existing solutions, in the sense that it is able to dynamically discriminate shear and plantar pressure during gait.