A fiber Bragg gratings (FBGs) based system, constituted by six sensors, for wheelchair users muscle effort monitoring was proposed. Each sensor consists in one FBG embedded in epoxy resin, which was secured to Kinesio tape through a 3D printed connection system. After the approval of the Ethics and Deontology Committee and the Data Protection Officer of the University of Aveiro (Portugal), the sensors were implemented to evaluate wheelchair users muscle effort. The sensors were placed on the biceps, deltoids, and triceps (three sensors in each arm) of four wheelchairs users’ volunteers, which were asked to perform several exercises. The arms’ muscle effort required was estimated through the FBGs wavelength shift, which was related with the deformation of the epoxy resin during some of the wheelchair users’ daily movements: varying the typical used hand patterns on horizontal plane (pattern A, B and D); vertical and inclined dips; and going up and down a ramp. The results reveal that on the horizontal plane, the movement characterized by minor hand swings in relation to the wheelchair rim (pattern A), requires a smaller muscle effort, and the dips were the exercise requested to wheelchair users which demand the highest and most sudden muscle effort applied in the arms. The proposed system may be used to monitor and quantify the muscle effort related to any movement, aiding on the choice of techniques to promote the reduction of the muscle fatigue, and therefore contributing to the improvement of wheelchair user quality of life.
In this work, a solution to monitor users’ activity within an indoor scenario is proposed. It is based on non-wearable and non-invasive sensing, and it is specially fitted for the elders’ home monitoring. The localization of a person is estimated through an optical sensing network that detects the floor vibration produced by the footstep when walking. Optical fiber Bragg sensors are integrated within high sensitive accelerometers to detect such vibration. Three similar accelerometers were developed from which sensitivities of 269 pm/G, 225 pm/G, and 209 pm/G were found. Allied to vibration detection, an algorithm is employed to retrieve one’s position from the data. In preliminary localization tests, the system has demonstrated an accuracy under 5 cm over a 3.2 m2 detection area, proving itself to be a promising solution for the targeted application.
In this paper, the design and implementation of a cost-effective interrogation architecture, for dynamic strain monitoring of in-line Fabry-Perot interferometric (FPI) optical fiber sensors is presented. The common interrogation techniques for this type of sensors are based in the full spectrum analysis, which render them not adequate for dynamic/high frequency monitoring applications. In this work, we propose an alternative cost-effective solution, based on a simplified edge-filter technique, for the dynamic monitoring of FPI sensing devices. The FPI based sensor was produced from the recycling of optical fiber previously damaged by the catastrophic fuse effect using precise splicing techniques. A characterization was performed with two different devices, an optical spectrum analyzer (OSA) and the proposed device leading to similar behavior and sensitivity values.
Magnetic field sensors have been widely applied in several areas, for instance, in navigation, geophysical, aerospace engineering and biomedical research. The traditional methods used to sense this parameter have drawbacks related with size, stability, multiplexing capability, remote measurement and electromagnetic sensitivity. Due to the characteristics inherent to the optical fiber, including small dimensions, immunity to electromagnetic interference and the possibility of being used in hazardous environments, this technology has great potential for sensing different parameters. In this work, the magnetic field was monitored using a Fabry-Perot micro-cavity. The cavity, produced from the recycling of optical fiber previously destroyed by the catastrophic fuse effect, was filled with magnetic fluid (MF). Then, it was exposed to a magnetic field in the range of 0 to 200 mT, applied transversally to the fiber axis. An overall exponential decrease of the wavelength of the reflection spectrum with the increase of the magnetic field was obtained, with a sensitivity and resolution of 120.5 ± 4.4 pm/mT and 8.3 μT, respectively, in the range of 0 to 80 mT (linear behavior). The proposed sensor represents a cost-effective solution for the magnetic field sensing, with an improved performance compared with other devices already reported in the literature.
Analysis of gait pattern of individuals is a very useful tool for the identification of locomotive motor anomalies, which can lead to early diagnosis and adequate treatment of patients with motor disorders. The knees are the lower limb joints exposed to major tension during human locomotion, presenting higher risk of a wider range of possible disorders. The devices used to monitor human joints should be comfortable and not restrain patients’ movement, while maintaining their resolution and accuracy. Most of current measurement techniques are based on electronic devices, which are often not adequate for demanding environments, such as the context of physical rehabilitation. We propose an e-Health sensing solution to dynamically monitor human knee angles during gait, using low-cost intrinsic Fabry-Perot interferometers optical fiber sensors (FPI-OFS). To the best of our knowledge, no previous efforts have reported the use of FPI sensors for such dynamic monitoring. The overall sensor consists of an optical fiber containing the FPI microcavity, which is embedded along the longitudinal direction of a kinesio tape (K-Tape), and placed along the knee rotation axis. Since the K-Tape has great adhesion to the skin, the FPI sensor is kept at the knee rotation axis, without restricting the user’s movements. During the knee flexion/extension, the K-Tape extends/compresses accordingly, resulting in the modulation of the reflected spectrum by the FPI-OFS. Several calibration and performance tests have been performed. Their results show the reliability and accuracy of the proposed solution, with sensibilities values of 53.8±2.4 pm/°.
This work reports the development of a bioinspired sensor capable of measuring vertical and shear (tangential) forces. The sensor is composed of two materials, the polylactide (PLA) and epoxy resin, combined with a photosensitive optical fiber with two fiber Bragg gratings (FBG1 and FBG2). The FBG1 was placed in a cavity filled with epoxy resin, while FBG2 was between the cavity and the shear wall that undergoes shear force. This FBGs’ encapsulation allowed one of them to be affected by vertical and shear forces (FBG1), while FBG2 was only affected by shear force. The calibration and performance tests were carried out with the aid of an electronic tri-axial force sensor. From these tests, sensitivities of K1V= 0.02±2.35x10-4 nm/N; K1S= 0.13±3.25x10-3 nm/N; K2V= -2.88x10-4±6.72x10-5 nm/N and K2S= -1.77±0.03 nm/N to each type of force, for FBG1 and FBG2, respectively, were achieved. The obtained results demonstrated the reliability of the developed solution, with a significant improvement of its sensitivity to shear force, and a low production complexity, when compared to other previously reported optical sensors.
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.
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.
This paper presents a simple, compact, stable and inexpensive in-line solution based on catastrophic fuse effect micro-cavity interferometers for edge-filter strain interrogation of a fiber Bragg grating sensor. By using a commercial spliced machine and recycling damage fiber for the catastrophic fuse effect it is possible to construct a micro-cavity with high contrast of more than 20dB, and acceptable half free spectra range (FSR) around 13nm of interrogation range. The strain from 0 to 1440μStrain of the FBG sensor is measured with evidences of high repeatability and stability. Future work will investigate the use of the proposed method for applications requiring higher interrogation rates.
Tilted fiber Bragg gratings (TFBGs) are one of the most attractive kind of optical fiber sensor technology due to their intrinsic properties. On the other hand, the acousto-optic effect is an important, fast and accurate mechanism that can be used to change and control several properties of fiber gratings in silica and polymer optical fiber. Several all-optical devices for optical communications and sensing have been successfully designed and constructed using this effect. In this work, we present the recent results regarding the production of optical sensors, through the acousto-optic effect in TFBGs. The cladding and core modes amplitude of a TFBG can be controlled by means of the power levels from acoustic wave source. Also, the cladding modes of a TFBG can be coupled back to the core mode by launching acoustic waves. Induced bands are created on the left side of the original Bragg wavelength due to phase matching to be satisfied. The refractive index (RI) is analyzed in detail when acoustic waves are turned on using saccharose solutions with different RI from 1.33 to 1.43.
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).
Optical fiber sensors has become one of the most promising sensing technologies. Within all the optical fiber sensing technologies, the Fabry-Perot interferometer (FPI) micro-cavities are one of the most attractive, due to the size, linearity and higher sensitivity. In this work we present the recent results, achieved by our group, regarding the production of optical sensors, by recycling optical fibers destroyed through the catastrophic fuse effect. This enabled the production of FPI sensors, in a cost effective way, tailored for the monitoring of several physical parameters, such as relative humidity (RH), refractive index (RI) and hydrostatic pressure.
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.
In this work, an optical fiber hydrostatic pressure sensor based in Fabry-Perot micro-cavities is presented. These micro structures were generated by the recycling of optical fiber previously damaged by the fiber fuse effect, resulting in a cost effective solution when compared with the traditional methods used to produce similar micro-cavities. The developed sensor was tested for pressures ranging from 20.0 to 190.0 cmH2O and a sensitivity of 53.7 ± 2.6 pm/cmH2O for hydrostatic pressures below to 100 cmH2O was achieved.
In the last decades the fiber Bragg gratings (FBG) and Fabry-Perot Interferometer (FPI) micro cavities based sensors have become one of the most attractive optical fiber sensing technologies. However, its production requires a significant economical investment. We propose a cost effective solution based on micro cavity generated by the recycling of optical fibers destroyed through the catastrophic fuse effect. This technique considerably reduces the experimental complexity and the production costs. In this paper, the application of these sensors in the monitoring of several parameters, such as refractive index, pressure, strain and temperature is presented.
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.
KEYWORDS: Sensors, Fiber Bragg gratings, Structural health monitoring, Laser range finders, Data acquisition, Earthquakes, Buildings, Temperature metrology, Phase shifts, Mirrors
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.