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Regenerated fiber Bragg grating sensing system for ultrasonic detection in a 900 °C environment
摘要： Heat-resistant composites, such as ceramic matrix composites (CMCs) and heat-resistant carbon fiber reinforced plastics (CFRPs), are expected to be used for aircraft engine parts. The development of reliable heat-resistant composite materials requires the use of nondestructive test (NDT) techniques for evaluating the progression of damage during material testing at elevated temperatures. Furthermore, structural health monitoring (SHM) technologies that operate under harsh environments are expected to be realized for monitoring heat-resistant composite structures. To provide potential solutions for the establishment of such technologies, this research developed a heat-resistant ultrasonic sensor based on a regenerated fiber-optic Bragg grating (RFBG). First, we fabricated an RFBG by annealing a normal FBG sensor. Because the RFBG exhibits high heat resistance at temperatures of 1000 °C, the sensor achieved stable ultrasonic detection at an elevated temperature. In addition, we attempted to use a π-phase-shifted FBG (PSFBG) as the seed grating to construct an ultrasonic sensor with enhanced performance. As a result, the R(PS)FBG sensor possessed a very short effective gauge length and achieved a broad frequency response to ultrasonic waves with frequencies greater than 1.5 MHz. The broadband detectability enables the R(PS)FBG sensor to acquire an accurate response to ultrasonic waves. Hence, we believe the regenerated Bragg grating-based ultrasonic sensors can contribute to establishing an effective nondestructive evaluation method for composite materials, thereby enabling a structural health monitoring system for a composite-made structure operating under extreme high-temperature environments.
关键词： structural health monitoring (SHM),ultrasonic detection,nondestructive test (NDT),regenerated fiber-optic Bragg grating (RFBG),high-temperature environment,Heat-resistant composites
更新于2025-09-04 15:30:14
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Design and Analysis of a Novel Phase-Shifted Bragg Grating for Bloch Surface Waves
摘要： A novel phase-shifted Bragg grating (PSBG) for Bloch surface waves (BSWs) propagating along the interface between a semiconductor thin layer and a multilayer stack is proposed. This structure is composed of a set of a special ridge fabricated on a multilayer stack supporting a Bloch surface wave. The multilayer stack is periodic, with the unit cell composed of two layers with different materials and thicknesses. The light con?nement capability and transmission properties of the proposed structure are investigated in the wavelength range of 1450–1650 nm by using the ?nite-element method and ?nite-difference time-domain method. Compared to existing PSBG structures based on surface plasmon polaritons waves, the proposed con?guration does not include any metal and the absorption losses upon propagation of the surface wave are negligibly small. Simulation results also indicate that the proposed structure exhibits outstanding transmission properties. The proposed PSBG for BSWs could be applied in narrow bandpass ?ltering, all optical computing, and enable on-chip integration photonic circuits.
关键词： resonance domain.,guided waves,Bloch surface waves,Phase-shifted Bragg grating
更新于2025-09-04 15:30:14
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[ASME ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering - Madrid, Spain (Sunday 17 June 2018)] Volume 11B: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering - Investigation on Temperature Compensation of Fiber Bragg Grating Sensors for Hull Monitoring
摘要： Hull monitoring system with Fiber Bragg Grating (FBG) sensors increasingly receives people's attentions. However, for the ship hull monitoring, the deformation of hull girder changes a lot as is subjected to a huge temperature variation. Therefore, the compensation method with only FBG temperature self-correction is not suitable for the hull monitoring sensors because no material thermal expansion effects are reasonably included. In this paper, the new compensation method of hull monitoring FBG sensor based on the sensor theory with both FBG temperature self-correction and steel thermal expansion effects correction is studied. The coupled compensation method suitable for hull monitoring sensor is obtained by theoretical derivation. As the comparison, the coupled compensation experiment was carried out. The results show that the relative error under the temperature compensation method is large in the case of drastic strain and temperature changes, and the correction results of the tested method will be closer to the true level.
关键词： temperature compensation,coupled compensation method,steel thermal expansion,hull monitoring,Fiber Bragg Grating (FBG) sensors
更新于2025-09-04 15:30:14
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Design and investigation of a dual-layer grating coupler for efficient vertical fiber-chip coupling
摘要： A novel dual-layer grating coupler was designed for efficient vertical coupling between a single-mode fiber and silicon nanowires, with characteristics of polarization diversity and both wavelength bands of 1.3 and 1.55 μm. Theoretical analysis and two-dimensional finite-difference time-domain simulations were applied to verify the performance of the design. Optimized results show that the coupling efficiencies of a dual-port output of 41% (?3.87 dB) for transverse-electric polarization at 1.56 μm, 32.88% (?4.83 dB) for transverse-magnetic (TM) polarization at 1.58 μm, and 27.06% (?5.68 dB) for TM polarization at 1.32 μm can be achieved. Dual-layer Fabry–Perot resonance was also investigated for high coupling efficiency.
关键词： silicon nanowires,dual-layer grating coupler,vertical fiber-chip coupling,polarization diversity,wavelength bands
更新于2025-09-04 15:30:14
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[IEEE 2018 Iranian Conference on Electrical Engineering (ICEE) - Mashhad (2018.5.8-2018.5.10)] Electrical Engineering (ICEE), Iranian Conference on - Tunable Filter by Using Parity Time (PT) Symmetric Periodic Array Electronic
摘要： A circuit model of a periodic array of PT-symmetric (gain/loss coupled) waveguides is reported for the design of a novel tunable filter. This model consists of a pair of coupled circuits, one with amplification resistance and the other with an equivalent attenuation. By varying the value of the gain/loss, one can control the size of bandgap and hence the allowed frequencies propagating within the structure. For a critical value of gain/loss, the eigenvalues merge and the gap disappears. As a result, all frequencies can pass the structure i.e, an all pass filter. The Q-factor of reflected frequency can be varied such that, tunable Q from 20 to greatest has been successfully realized in the central frequency of 0.283 MHz. The remarkable feature of this design lies with its tunability, high speed, and relative simplicity.
关键词： RLC Circuit Model,Parity-Time (PT) Symmetry,Grating Waveguides,Optical Waveguides,Band Stop Filter (BSF)
更新于2025-09-04 15:30:14
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A Fiber Bragg-Grating-Based Miniature Sensor for the Fast Detection of Soil Moisture Profiles in Highway Slopes and Subgrades
摘要： A fiber Bragg grating (FBG)-based aluminum oxide tube packed sensor (ATPS) was developed for the fast detection of the soil moisture profile in highway slopes and subgrades. The novel ATPS consists of an aluminum oxide tube with a diameter of 5 mm, an optical fiber containing a quasi-distributed FBG sensors, a “U”-shaped resistance wire, and a flange. There are four 0.9-mm diameter holes in the ATPS. Laboratory experiments were carried out to calibrate the relationship between the thermal response of ATPS and the soil moisture content. Two laboratory rainfall validation model tests were performed to validate the ATPS for capturing the soil moisture profile in highway slopes and subgrades. During the validations, the accuracy of the ATPS was quantified, and water infiltration through grassy and grassless ground surfaces were investigated. The calibrations indicate that the ATPS can detect and record real-time changes in the highway slope and subgrade moisture after rainfall, and reveal the most dangerous zones that occur at the connection between different construction materials. The average measurement accuracy of soil moisture monitoring was 0.015 m3/m3. Please note that the connection is where cracks form easily and the soil hydraulic conductivity increases significantly. The test results also indicate that grassy cover (lawn) significantly prevents water infiltration during the first few minutes of rainfall (twelve minutes in this study), after which, however, the infiltration rate drops sharply. The influence of lawn on water infiltration depends on the soil structure, hydraulic conductivity, and rainfall time. In summary, due to its small size and fast detection, the ATPS is a portable probe that can be used for moisture monitoring in highway slopes and subgrades.
关键词： temperature sensing,aluminum oxide tube packed sensor (ATPS),highway slope and subgrade,fiber Bragg grating (FBG),soil moisture
更新于2025-09-04 15:30:14