The Experts below are selected from a list of 3021 Experts worldwide ranked by ideXlab platform

S Gali - One of the best experts on this subject based on the ideXlab platform.

  • Residual strain measurement in bonded composite repairs for aging aircraft by Embedded Fiber Bragg grating sensors
    Third European Workshop on Optical Fibre Sensors, 2007
    Co-Authors: Uri Ben-simon, Y Botsev, A K Green, G Ghilai, N Gorbatov, I Kressel, S Gali
    Abstract:

    Embedded Fiber-Bragg-Grating sensors are used for tracking the initiation of structural bonding and measuring the residual strains, during the curing process, of bonded composite patches used for aging aircraft structural repairs. FBG reading are shown to have direct correlation with the residual strains that are important in assessing the long-term durability of the repaired structure under fatigue load spectrum.

  • Practical strain isolation in Embedded Fiber Bragg gratings
    Smart Materials and Structures, 2005
    Co-Authors: E Shafir, G Berkovic, Yair Sadi, S Rotter, S Gali
    Abstract:

    We describe a new method for isolating Embedded Fiber Bragg gratings from strain. The strain isolated grating may serve as a pure temperature sensor in environments where both strain and temperature variations occur. The grating need not be at the end of the Fiber, thus enabling multiplexing of several strain-isolated gratings along a single Fiber.

  • Polarization mode dispersion in radio-frequency interferometric Embedded Fiber-optic sensors
    Journal of Lightwave Technology, 2001
    Co-Authors: A. Eyal, O. Dimenstein, M. Zaidman, A. Green, S Gali
    Abstract:

    The effect of Fiber birefringence on the propagation delay in an Embedded Fiber-optic strain sensor is studied. The polarization characteristics of the sensor are described in terms of polarization mode dispersion through the principal states of polarization and their differential group delay. Using these descriptors, an analytical expression for the response of the sensor for an arbitrary input state of polarization is given and experimentally verified. It is found that the differential group delay, as well as the input and output principal states of polarization, vary when the Embedded Fiber is strained, leading to fluctuations in the sensor output. The use of high birefringence Fibers and different embedding geometries is examined as a means for reducing the polarization dependency of the sensor.

Pengcheng Geng - One of the best experts on this subject based on the ideXlab platform.

  • Fiber modal interferometer with Embedded Fiber bragg grating for simultaneous measurements of refractive index and temperature
    Sensors and Actuators B-chemical, 2013
    Co-Authors: Weigang Zhang, Hao Zhang, Pengcheng Geng
    Abstract:

    Abstract A highly sensitive and compact Fiber-optic sensor for simultaneous measurement of refractive index (RI) and temperature has been proposed and experimentally demonstrated. The device is based on a Fiber modal interferometer assisted by an Embedded Fiber Bragg grating, which helps to resolve the crosstalk issue. The Fiber modal interferometer consists of an Up-Fusion-Bitaper (UFBT) pair to excite high-order cladding-modes and re-couple them to the Fiber core. For high order cladding mode involved in the interference, the implemented sensor yields high spectral sensitivities of −197.03 ± 7.35 nm/RIU (refractive index unit) for a refractive index (RI) range of 1.365–1.415 and 63.7 ± 1.84 pm/°C for a temperature range from 20 to 80 °C, respectively. Simultaneous measurement of ambient RI and temperature has been experimentally demonstrated. The maximum RI and temperature measurement errors are ±0.00054 RIU and ±0.77 °C, respectively. These results demonstrate the feasibility of this configuration for reliable RI-based chemical and biochemical monitoring.

  • Fiber modal interferometer with Embedded Fiber Bragg grating for simultaneous measurements of refractive index and temperature
    Sensors and Actuators B: Chemical, 2013
    Co-Authors: Shecheng Gao, Zhiyong Bai, Wei Lin, Bo Liu, Pengcheng Geng, Weigang Zhang, Hao Zhang, Xiaolin Xue
    Abstract:

    A highly sensitive and compact Fiber-optic sensor for simultaneous measurement of refractive index (RI) and temperature has been proposed and experimentally demonstrated. The device is based on a Fiber modal interferometer assisted by an Embedded Fiber Bragg grating, which helps to resolve the crosstalk issue. The Fiber modal interferometer consists of an Up-Fusion-Bitaper (UFBT) pair to excite high-order cladding-modes and re-couple them to the Fiber core. For high order cladding mode involved in the interference, the implemented sensor yields high spectral sensitivities of -197.03 ± 7.35 nm/RIU (refractive index unit) for a refractive index (RI) range of 1.365-1.415 and 63.7 ± 1.84 pm/ C for a temperature range from 20 to 80 C, respectively. Simultaneous measurement of ambient RI and temperature has been experimentally demonstrated. The maximum RI and temperature measurement errors are ±0.00054 RIU and ±0.77 C, respectively. These results demonstrate the feasibility of this configuration for reliable RI-based chemical and biochemical monitoring. © 2013 Elsevier B.V.

Michael Todd - One of the best experts on this subject based on the ideXlab platform.

  • Impact Detection and Characterization in Composite Laminates with Embedded Fiber Bragg Gratings
    Procedia Engineering, 2017
    Co-Authors: Michael Yeager, Anthony Whittaker, Chris Key, Hyonny Kim, Michael Todd, William Gregory
    Abstract:

    The use of composite materials has expanded significantly across civil, aerospace, and marine structures in both new designs and retrofits. The performance benefits from composites-typically, weight reduction with increased strength, corrosion resistance, and improved thermal and acoustic properties-are challenged by a host of failure modes whose genesis and progression aren't yet well understood. As such, structural health monitoring (SHM) plays a key role for in-situ assessment for the purposes of performance/operations optimization, maintenance planning, and overall life cycle cost reduction. In this work, arrays of Fiber Bragg grating optical strain sensors are Embedded into a pre-preg composite specimen that was designed by surrogate finite element model simulation, and will be subjected to both low-energy (non-damaging) impacts at various locations and high-energy damaging impacts at a known location. The impactor was designed along with the panel specimen for very specific energy levels, strain frequency, and strain amplitude response. Results from SHM algorithms developed via hypothesis testing are demonstrated on blind impact tests in order to determine the efficacy of Embedded Fiber Bragg grating arrays for assessing structural health of such composites.

  • A method for monitoring bolt torque in a composite connection using an Embedded Fiber Bragg grating sensor
    Journal of Intelligent Material Systems and Structures, 2017
    Co-Authors: Mike Yeager, Anthony Whitaker, Michael Todd
    Abstract:

    This work presents a new method for monitoring the preload torque in a composite bolted connection using an Embedded Fiber Bragg grating sensor. A unique washer was designed to impose a specified nonuniform strain field across the grating, causing distortion in the reflected optical spectrum. Using the full-width at half maximum bandwidth of the Bragg reflection spectrum as the preload-sensitive feature, it is shown that this feature increases monotonically—and quite linearly—with increasing applied bolt torque. It is also demonstrated that, although distorted, the spectral structure of the sensor is maintained such that it is simultaneously able to function in its typical use as a uniaxial strain sensor, thus essentially creating a dual-purpose sensor. The computational design approach is validated with a prototype experiment.

  • Assessment of Embedded Fiber Bragg gratings for structural health monitoring of composites
    Structural Health Monitoring, 2017
    Co-Authors: Mike Yeager, William Gregory, Michael Todd, Chris Key
    Abstract:

    This work provides a system-level investigation into the use of Embedded Fiber Bragg grating optical sensors as a viable sensing architecture for the structural health monitoring of composite structures. The practical aspects of the embedding process are documented for both carbon Fiber–reinforced polymer and glass Fiber–reinforced polymer structures manufactured by both oven vacuum bag and vacuum-assisted resin transfer method processes. Initially, Embedded specimens were subject to long-term water submersion to verify performance in an underwater environment. A larger, more complex jointed specimen was also fabricated with a fully Embedded sensor network of Fiber Bragg gratings and subjected to incrementally induced bearing damage. Using commercially available interrogation hardware, a damage detection structural health monitoring algorithm was developed and deployed. The results permit statistically precise detection of low levels of connection damage in the composite specimen.

Nam Quoc Ngo - One of the best experts on this subject based on the ideXlab platform.

  • Shear force sensing by strain transformation using non-rectilinearly Embedded Fiber Bragg grating
    Sensors and Actuators A: Physical, 2004
    Co-Authors: Rupali Suresh, Swee Chuan Tjin, Nam Quoc Ngo
    Abstract:

    This paper presents a new method of shear force measurement using Fiber Bragg grating (FBG) as the sensing element. In this sensor, the FBG is Embedded in such a way that the applied shear strain is transformed as an equivalent axial strain in the Embedded Fiber. The basic sensor design consists of layers of carbon composite material (CCM) and deformable layer with an Embedded FBG at a very small angle. With this embedding technique, a linear variation of the reflected Bragg wavelength shift with the applied shear force is observed. The sensor was tested with an applied force of 40N. A good sensitivity of 81pm/N is found for this sensor, which is suitable for most engineering applications. Failure test of the sensor shows that the sensor can withstand a maximum shear force of 67N. This paper presents the basic principle, the embedding technique and the parametric study of the sensor. © 2004 Elsevier B.V. All rights reserved.

Mike Yeager - One of the best experts on this subject based on the ideXlab platform.

  • A method for monitoring bolt torque in a composite connection using an Embedded Fiber Bragg grating sensor
    Journal of Intelligent Material Systems and Structures, 2017
    Co-Authors: Mike Yeager, Anthony Whitaker, Michael M. Todd
    Abstract:

    This work presents a new method for monitoring the preload torque in a composite bolted connection using an Embedded Fiber Bragg grating sensor. A unique washer was designed to impose a specified n...

  • A method for monitoring bolt torque in a composite connection using an Embedded Fiber Bragg grating sensor
    Journal of Intelligent Material Systems and Structures, 2017
    Co-Authors: Mike Yeager, Anthony Whitaker, Michael Todd
    Abstract:

    This work presents a new method for monitoring the preload torque in a composite bolted connection using an Embedded Fiber Bragg grating sensor. A unique washer was designed to impose a specified nonuniform strain field across the grating, causing distortion in the reflected optical spectrum. Using the full-width at half maximum bandwidth of the Bragg reflection spectrum as the preload-sensitive feature, it is shown that this feature increases monotonically—and quite linearly—with increasing applied bolt torque. It is also demonstrated that, although distorted, the spectral structure of the sensor is maintained such that it is simultaneously able to function in its typical use as a uniaxial strain sensor, thus essentially creating a dual-purpose sensor. The computational design approach is validated with a prototype experiment.

  • Assessment of Embedded Fiber Bragg gratings for structural health monitoring of composites
    Structural Health Monitoring, 2017
    Co-Authors: Mike Yeager, William Gregory, Michael Todd, Chris Key
    Abstract:

    This work provides a system-level investigation into the use of Embedded Fiber Bragg grating optical sensors as a viable sensing architecture for the structural health monitoring of composite structures. The practical aspects of the embedding process are documented for both carbon Fiber–reinforced polymer and glass Fiber–reinforced polymer structures manufactured by both oven vacuum bag and vacuum-assisted resin transfer method processes. Initially, Embedded specimens were subject to long-term water submersion to verify performance in an underwater environment. A larger, more complex jointed specimen was also fabricated with a fully Embedded sensor network of Fiber Bragg gratings and subjected to incrementally induced bearing damage. Using commercially available interrogation hardware, a damage detection structural health monitoring algorithm was developed and deployed. The results permit statistically precise detection of low levels of connection damage in the composite specimen.