Mohamed Zaghloul

Sapphire Fiber Optical Hydrogen Sensors for High-Temperature Environments

This letter presents a high-temperature fiber optical hydrogen sensor with operational temperatures up to 800 °C. The sensor is based on a single-crystal sapphire fiber coated with Pd nanoparticles incorporated TiO2 nanostructured thin film. The template-based sol-gel chemistry was applied to synthesize the nanostructured porous thin films. The sensitivity and response time of the sensor was evaluated for hydrogen concentrations varying from 0.02% to 4%. The effects of temperature on the hydrogen gas sensing properties were investigated from 600 °C to 800 °C.

High resolution monitoring of strain fields in concrete during hydraulic fracturing processes

We present a distributed fiber optic sensing scheme to image 3D strain fields inside concrete blocks during laboratory-scale hydraulic fracturing. Strain fields were measured by optical fibers embedded during casting of the concrete blocks. The axial strain profile along the optical fiber was interrogated by the in-fiber Rayleigh backscattering with 1-cm spatial resolution using optical frequency domain reflectometry (OFDR). The 3D strain fields inside the cubes under various driving pressures and pumping schedules were measured and used to characterize the location, shape, and growth rate of the hydraulic fractures. The fiber optic sensor detection method presented in this paper provides scientists and engineers an unique laboratory tool to understand the hydraulic fracturing processes via internal, 3D strain measurements with the potential to ascertain mechanisms related to crack growth and its associated damage of the surrounding material as well as poromechanically-coupled mechanisms driven by fluid diffusion from the crack into the permeable matrix of concrete specimens.

Discrimination of Temperature and Strain in Brillouin Optical Time Domain Analysis Using a Multicore Optical Fiber

Brillouin optical time domain analysis is the sensing of temperature and strain changes along an optical fiber by measuring the frequency shift changes of Brillouin backscattering. Because frequency shift changes are a linear combination of temperature and strain changes, their discrimination is a challenge. Here, a multicore optical fiber that has two cores is fabricated. The differences between the cores’ temperature and strain coefficients are such that temperature (strain) changes can be discriminated with error amplification factors of 4.57 °C/MHz (69.11 μϵ/MHz), which is 2.63 (3.67) times lower than previously demonstrated. As proof of principle, using the multicore optical fiber and a commercial Brillouin optical time domain analyzer, the temperature (strain) changes of a thermally expanding metal cylinder are discriminated with an error of 0.24% (3.7%).

Radiation resilient fiber Bragg grating sensors for sensing applications in nuclear reactor cores

This paper reports testing results of radiation resilient fiber Bragg grating (FBG) in radiation resistant fibers in the nuclear reactor core at MIT Research Reactor Lab. FBGs were fabricated by 140-fs ultrafast laser pulse using a phase mask approach. In-core test of fiber Bragg gratings was carried out in the core region of a 6-MW research reactor at temperature > 600°C and an average fast neutron (>1 MeV) flux >1×1014 n/s/cm2. First 100-day tests of FBG sensors shows less than 5 dB reduction in FBG peak strength after over 1×1020 n/cm2 of accumulated fast neutron dosage. To test temporal responses of FBG sensors, a number of reactor anomaly events were artificially created to abruptly change reactor power, temperature, and neutron flux over short periods of time. The thermal optical coefficients and temporal responses of FBG sensors are determined at different accumulated dosages of neutron flux. Results presented in this paper reveals that temperature-stable Type-II FBGs fabricated in radiation-hardened fibers could be used as sensors to perform in-pile measurements to improve safety and efficiency of existing and next generation nuclear reactors.

Dual-core optical fibers for simultaneous measurements of temperature and strain using Brillouin OTDA

We report a dual-core fiber for simultaneous sensing of strain and temperature using BOTDA. By adjusting dopant compositions, 37% difference in strain-optical coefficient was achieved between two cores to differentiate temperature and strain responses.

High spatial resolution fiber optical sensors for simultaneous temperature and chemical sensing for energy industries

This paper demonstrates optical fibers as high-temperature sensor platforms. Through engineering and onfiber integration of functional metal oxide sensory materials, we report the development of an integrated sensor solution to perform temperature and chemical measurements for high-temperature energy applications. Using the Rayleigh optical frequency domain reflectometry (OFDR) distributed sensing scheme, the temperature and hydrogen concentration were measured along the fiber. To overcome the weak Rayleighbackscattering intensity exhibited by conventional optical fibers, an ultrafast laser was used to enhance the Rayleigh scattering by a direct laser writing method. Using the Rayleigh-enhanced fiber as sensor platform, both temperature and hydrogen reaction were monitored at high temperature up to 750°C with 4-mm spatial resolution.

High Spatial Resolution Radiation Detection Using Distributed Fiber Sensing Technique

This paper studies perspectives on using optical fibers and distributed fiber sensing schemes to perform real-time-distributed gamma-ray radiation sensing with high spatial resolution. The radiation-induced optical property changes of aluminum-doped fibers were studied using cobalt-60 sources. The distributed optical loss of the aluminum-doped fiber was characterized using the Rayleigh backscattering optical frequency domain reflectometry (Rayleigh OFDR). The optical loss of unprotected fiber under various gamma dose rates remains linear up to 100 grays (Gy). Using the gamma radiation-sensitive fiber, the localized optical loss measured by the Rayleigh OFDR was used to map the accumulated gamma radiation dosage on the entire surface of the cylinder with a 1-cm spatial resolution. Using electrical cables as a ubiquitous sensor platforms for fiber sensor deployment, this paper explores the potential for multifunctional distributed fiber sensor by integrating distributed fiber temperature and gamma ionizing radiation sensors in electrical cables for multifunctional measurements to improve the safety of nuclear power systems at both the component and system levels. As sensors that can readily be embedded in a wide variety of materials and structures, radiation-sensitive fibers can be low-cost and highly flexible tool to gauge the performance degradation and longevity of materials and components used in the nuclear power systems.

Dual-Core Fiber Characterizations for Distributed Simultaneous Temperature and Strain Measurements Using Brillouin Optical Time Domain Analysis

This paper reports characterizations of dual-core optical fiber designed for simultaneous temperature and strain measurements using Brillouin optical time domain analysis

Ultra-high temperature fiber optical chemical sensors based on nano-porous metal oxides

This paper presents fiber optical gas sensors based on nano-porous metal oxide functional materials for high-temperature energy applications. A solution-based approach was used to produce nano-porous functional metal oxide and their dopant variants as sensing films, which was integrated on high-temperature stable FBGs in D-shaped silica fibers and sapphire fibers. The Bragg grating peaks were used to monitor the refractive index change and optical absorption loss due to the redox reaction between Pd-doped TiO2 and hydrogen from the room temperature to 800°C. The experimental results show the sensors response is reversible for hydrogen concentration between 0.1 vol.% to 5 vol. %. The response time of the hydrogen sensor is <8s.