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Response Time of a Fiber Bragg Grating Based Hydrogen Sensor for Transformer Monitoring
摘要： We developed and optimized a new fiber optic sensor using palladium foils attached to optical fiber Bragg gratings (FBG) for hydrogen measurements. Fifteen in parallel processed sensors were characterized and qualified in two custom tailored experimental set ups and their response to a 5% hydrogen/nitrogen gas mixture and the same gas bubbled trough transformer oil was measured. The hydrogen response is similar for both medium and close to the theoretical maximum sensitivity, but the response time was found to be very different, much slower in oil than in gas. A theoretical comparison of hydrogen diffusion trough palladium and hydrogen absorption on the palladium surface as well as a measurement of the hydrogen uptake and diffusion trough the oil to the sensor have been done to investigate the origin of the different response time. They indicate that the response time determining step is the absorption of hydrogen on the palladium surface and that this process is slowed down in oil compared to a pure gas environment.
关键词： hydrogen sensor,fibre Bragg grating (FBG),fiber sensor,palladium based sensors,hydrogen diffusion and absorption in oil
更新于2025-09-23 15:22:29
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Optical Characteristics of Zinc Oxide Films on Glass Substrates
摘要： An algorithm is developed for solving the inverse problem of multiangular spectrophotometry of a layer on a plane-parallel substrate of finite thickness using s- and p-polarized waves. It allows the dispersive properties of the layer and substrate to be studied both far from and in the vicinity of the resonant wavelengths. The dispersive properties of layers of pure and Al-doped ZnO on glass substrates are investigated using it. It is shown that doping shifts the absorption band maximum to shorter wavelength and decreases the refractive index of the material. The applicability limits of known approximate expressions for determining the spectral dependence of the absorption coefficient of a layer from spectrophotometric data are estimated.
关键词： band gap,refractive index and absorption coefficient,multiangular spectrophotometry,ZnO
更新于2025-09-23 15:22:29
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Kinetics of graphitization of thin diamond-like carbon (DLC) films catalyzed by transition metal
摘要： In this paper, we have studied the kinetics of graphitization at 773K of thin diamond-like carbon (DLC) films coated with minute amount of Ni metallic particles. DLC films are deposited at room temperature by pulsed laser deposition (PLD) on a transparent quartz substrate, and Ni is deposited on the surface of DLC using molecular beam epitaxy technique at room temperature. The ultra-high vacuum thermal (range 573-873K with 60 min annealing treatments) and kinetic (range 30-3760 min at 773K) behaviors of the deposited films are investigated. Surface and interface characterizations indicate that the growth of graphitic sp2 clusters starts at temperatures lower than 573K. The kinetics of graphitization is recorded at 773K. Thus, the continuous growth of graphitic clusters leads to a long-range kinetics. These clusters are responsible for the increase in the electrical conductivity and carrier mobility, reaching values of 6.103 Siemens/cm and 20 V/cm2?s, respectively. This continuous change is not only explained by the nucleation and growth of graphitic clusters, but also by some reorientation of them alongside both the surface and the quartz substrate. The obtained results demonstrate that thermally post-treated catalytic metal/DLC films are promising materials for conductive electrodes and sensing applications.
关键词： Raman spectroscopy,thermal treatment,electric transport measurements,optical transmission and absorption,diamond-like carbon,thin graphite films,pulsed laser deposition,metal catalyst
更新于2025-09-23 15:21:01
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[IEEE 2018 Australasian Universities Power Engineering Conference (AUPEC) - Auckland, New Zealand (2018.11.27-2018.11.30)] 2018 Australasian Universities Power Engineering Conference (AUPEC) - Nano-structured GaAs Solar Cell Design, Simulation and Analysis for Conversion Efficiency Improvement
摘要： This paper discusses nano-structured GaAs solar cell design and analysis for conversion efficiency improvement by increasing the light transmission and absorption, reducing the light reflection. The focus of this research is to construct different type of nano-grating shaped GaAs solar cells with various nano-grating heights and pitches, to compare the simulation results and find a suitable nano-structure that can provide higher conversion efficiency. Finite difference time domain (FDTD) simulation tool is used to simulate and calculate transmission and absorption for different nano-grating shapes, such as, parabolic, triangular, trapezoidal and rectangular. Based on the simulation results, it has been confirmed that the light reflection of parabolic shaped nano-grating structures is higher than triangular nano-grating structures, but it is lower than rectangular and trapezoidal shaped nano-grating structures. Moreover, the simulation results confirmed that the light transmission of parabolic shaped nano-grating structures is about 62.3% having a 200-nm grating height and an 810-nm grating pitch, which is about 22% higher than the rectangular (i.e., flat) type substrates.
关键词： Finite-difference time-domain method,transmission,GaAs solar cells,and absorption,Nano-grating structure,Light reflection,Conversion efficiency,Solar or renewable energy
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - InP Quantum Dot Mode-Locked Lasers and Materials Studies
摘要： InP/GaInP quantum dot laser structures exhibiting broad optical gain spectra suitable for mode-locking have been demonstrated. Two-section narrow ridge passive mode-locked lasers were fabricated from this material. Mode-locking conditions have been investigated for devices with different cavity lengths, with maximum frequency of 15.21 GHz.
关键词： Mode-Locked Lasers,InP Quantum Dots,Optical gain and absorption
更新于2025-09-11 14:15:04
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High-frequency absorption properties of gallium weakly doped barium hexaferrites
摘要： The BaFe12-xGaxO19 (x < 1.2) hexaferrites were synthesised by usual ceramics technology. The Bi2O3 additive in the amount of 3 wt% was applied. The features of crystal structure and unit cell parameters were re?ned using powder X-ray di?raction at 300 K. It is shown that with the substitution level increase the parameters of unit cell monotonically decrease. The magnetisation and susceptibility versus temperature and ?eld for these solid solutions were investigated by the vibration magnetometry method. The main magnetic concentration dependence is shown that with the substitution level the magnetic parameters increase monotonically decrease. The microwave properties of the samples including the external magnetic bias ?eld are also investigated at 300 K. It is shown that with the increase of Ga3+ concentration from x = 0.1 to x = 0.6 the frequency value of natural ferromagnetic resonance (NFR) decreases in the beginning, and at further increase in concentration up to x = 1.2 it increases again. With the increase in Ga3+ concentration, the line width of the NFR increases that indicates the increase of frequency range where there is an intensive absorption of electromagnetic radiation (EMR). At the same time, the peak amplitude of the resonant curve changes slightly. The frequency shift of NFR in the external magnetic bias ?eld takes place more intensively for the samples with small Ga3+ concentration. It is shown the prospects of use of the Ga-substituted barium hexagonal ferrite as the material e?ectively absorbing the high-frequency EMR.
关键词： crystal structure,doped hexaferrites,magnetic and absorption measurements,Solid-state reactions
更新于2025-09-09 09:28:46