M. Fátima Domingues

Optical Fiber Microcavity Strain Sensors Produced by the Catastrophic Fuse Effect

We present an innovative and cost effective approach to produced sensors based on optical fiber microcavities. The proposed microcavities were manufactured by splicing a standard optical fiber with recycled optical fibers destroyed by the catastrophic fuse effect, yielding strain sensors with sensitivity up to 2.56 pm·με-1. The feasibility of this solution employing recycled optical fibers was demonstrated, presenting an economical solution for sensing purposes, when compared with cavities produced using complex methods. We also show, for the first time, that the sensitivity of these microcavities Fabry-Perot interferometers sensors depends on the cavity volume.

Lithium batteries temperature and strain fiber monitoring

Fiber Bragg grating sensors were attached to the surface of a rechargeable lithium battery in order to monitor its thermal and strain fluctuations through charge and different discharge C rates. During the discharge process above 1C, it were observed, a temperature and strain fluctuations of a 4.12 ± 0.67 °C and 24.64 ± 6.02 με, respectively. In the regular charge process, a temperature and strain variation of 1.03 ± 0.67 °C and 15.86 ± 6.02 με, were detected.

Mobile caching-enabled small-cells for delay-tolerant e-Health apps

With the wide adoption of Internet of Things (IoT) and specifically e-Health applications, the nature of mobile applications, the increased traffic and the increasing number of connected devices are changing the requirements of wireless mobile networking. Addressing such foreseen increase in number of connected mobile devices, our work proposes a new trend of on-demand mobile small-cells with caching capabilities for e-Health applications. The solution targets delay-tolerant monitoring e-Health applications, with optional ultra-low latency communications for emergencies. The proposed networking architecture supports user mobile devices acting as small-cells with caching capabilities, for later transmission, when efficient high data rate communication conditions exist. The solution supports immediate high data-rate low-latency transmission for emergency situations. The proposed system enhances the performance of cellular networks, by saving on valuable scarce bandwidth and radio resources, while decreasing interference. Self-organizing networking is used for the further optimization of the network performance. The paper discusses performance gains resulting from mobile small cell deployment.

Insole optical fiber sensor architecturefor remote gait analysis - an eHealth Solution

The advances and fast spread of mobile devices and technologies, we witness today, have extended its advantages over medical and health practice supported by mobile devices, giving rise to the growing research of Internet of Things (IoT), especially the e-Health field. The features provided by mobile technologies revealed to be of major importance when we consider the continuous aging of population and the consequent increase of its debilities. In addition to the increase of lifetime span of population, also the increase of health risks and their locomotive impairments increases, requiring a close monitoring and continuous evaluation. Such monitoring should be as noninvasive as possible, in order not to compromise the mobility and the day-to-day activities of citizens. Therefore, we present the development of a noninvasive optical fiber sensor (OFS) architecture adaptable to a shoe sole for plantar pressure remote monitoring, which is suitable to be integrated in an IoT e-Health solution to monitor the wellbeing of individuals. This paper explores the production of the OFS multiplexed network (using fiber Bragg gratings) to monitor the foot plantar pressure distribution during gait (walking movement). From the acquired gait data, it is possible to infer health conditions of the patient’s foot and spine posture. To guarantee the patients mobility, the proposed system consists of an OFS network integrated with a wireless transceiver to enable efficient ubiquitous monitoring of patients. This paper shows the calibration and measurement results, which reflect the accuracy of the proposed system, under normal walking in controlled area.

Biaxial optical fiber sensor based in two multiplexed Bragg gratings for simultaneous shear stress and vertical pressure monitoring

This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.

Arterial pulses assessed with FBG based films: a smart skin approach

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.

Optical strain sensor based on FPI micro-cavities produced by the fiber fuse effect

In this work we present a cost effective strain sensor based on micro-cavities produced through the re-use of optical fibers destroyed by the catastrophic fuse effect. The strain sensor estimated sensitivity is 2.22 ±0.08 pm/μƐ. After the fuse effect, the damaged fiber becomes useless and, consequently, it is an economical solution for sensing proposes, when compared with the cavities produced using other complex methods. Also, the low thermal sensitivity is of great interest in several practical applications, allowing eluding cross-sensitivity with less instrumentation, and consequently less cost.

Dual scale structural health monitoring system combining FBG sensors and laser scanning

This work reports a case study of a structural health monitoring (SHM) system combining large and micro scale measurements installed in a 16th Century Church in Aveiro. This dual scale SHM system relies on a network of 24 fibre Bragg grating (FBG) sensors to perform micro scale, high resolution displacement and temperature measurements in several key points of the structure, while the large scale measurements are ensured by a scanning laser range finder. The results demonstrate that the developed systems allow adequate monitoring of the evolution of deformation in buildings, in different scales, keeping the visual impact in the structure reduced to a minimum and contributing for the implementation of best practices for rehabilitation of historic and cultural heritage.