Uniform Power Density Research Articles

Limitations of Bulk Diamond Sensors for Single-Cell Thermometry.

The present paper reports on a Finite Element Method (FEM) analysis of the experimental situation corresponding to the measurement of the temperature variation in a single cell plated on bulk diamond by means of optical techniques. Starting from previous experimental results, we have determined-in a uniform power density approximation and under steady-state conditions-the total heat power that has to be dissipated by a single cell plated on a glassy substrate in order to induce the typical maximum temperature increase ΔTglass=1 K. While keeping all of the other parameters constant, the glassy substrate has been replaced by a diamond plate. The FEM analysis shows that, in this case, the maximum temperature increase is expected at the diamond/cell interface and is as small as ΔTdiam=4.6×10-4 K. We have also calculated the typical decay time in the transient scenario, which resulted in τ≈ 250 μs. By comparing these results with the state-of-the-art sensitivity values, we prove that the potential advantages of a longer coherence time, better spectral properties, and the use of special field alignments do not justify the use of diamond substrates in their bulk form.

The Laser Alloying Process of Ductile Cast Iron Surface with Titanium Powder in Nitrogen Atmosphere

The article presents the results of the laser alloying process of a ductile cast iron EN-GJS 350-22 surface with titanium powder in nitrogen atmosphere. The aim of this research was to test the influence of nitrogen atmosphere on the structure and properties of the ductile cast iron surface layer produced by a laser alloying process with titanium. The laser alloying process was conducted using a Rofin Sinar DL020 2 kW high-power diode laser (HPDDL) with rectangular focus and uniform power density distribution in the focus axis. The tests of the produced surface layers included macrostructure and microstructure observations, X-ray diffraction (XRD) analysis, energy-dispersive spectroscopy (EDS) on scanning electron microscope (SEM) and transmission electron microscope (TEM), Vickers hardness and solid particle erosion according to ASTM G76-04 standard. As a result of the laser alloying process in nitrogen atmosphere with titanium powder, the in situ metal matrix composite structure reinforced by TiCN particles was formed. The laser alloying process of ductile cast iron caused the increased hardness and erosion resistance of the surface.

Theoretical and Experimental Studies on MEMS Variable Cross-Section Cantilever Beam Based Piezoelectric Vibration Energy Harvester.

The piezoelectric vibration energy harvester (PVEH) based on the variable cross-section cantilever beam (VCSCB) structure has the advantages of uniform axial strain distribution and high output power density, so it has become a research hotspot of the PVEH. However, its electromechanical model needs to be further studied. In this paper, the bidirectional coupled distributed parameter electromechanical model of the MEMS VCSCB based PVEH is constructed, analytically solved, and verified, which laid an important theoretical foundation for structural design and optimization, performance improvement, and output prediction of the PVEH. Based on the constructed model, the output performances of five kinds of VCSCB based PVEHs with different cross-sectional shapes were compared and analyzed. The results show that the PVEH with the concave quadratic beam shape has the best output due to the uniform surface stress distribution. Additionally, the influence of the main structural parameters of the MEMS trapezoidal cantilever beam (TCB) based PVEH on the output performance of the device is theoretically analyzed. Finally, a prototype of the Aluminum Nitride (AlN) TCB based PVEH is designed and developed. The peak open-circuit voltage and normalized power density of the device can reach 5.64 V and 742 μW/cm3/g2, which is in good agreement with the theoretical model value. The prototype has wide application prospects in the power supply of the wireless sensor network node such as the structural health monitoring system and the Internet of Things.

Wideband circularly polarised antenna array with isoflux pattern

The authors present a wideband circularly polarised antenna array consisting of a 10-element ellipse dipole antenna and a feed network. A metal pillar is vertically loaded at the end of each ellipse dipole arm to extend the current path, thereby reducing the lateral dimension of the antenna element. For uniform coverage over the Earth's surface, antenna with an isoflux pattern is required due to its uniform power density over a wide coverage area. To obtain wideband and isoflux characteristics, the amplitude and phase distributions along the network are optimised by applying the hybrid of the genetic algorithm and particle swarm optimisation. Particularly, the feed network with broadband phase shifting performance is designed to attain a broad bandwidth requirement. The proposed antenna can achieve excellent impedance matching and axial ratio characteristics from 1.1 to 1.6 GHz. In addition, the isoflux radiation pattern is obtained with the beamwidth of ±21° where the gain is higher than 0 dBi in the elevation plane (xoz-Plane). The realised gain is better than 10.2 dBi and the side lobes are below −14.2dB across the operating frequency. Finally, the antenna array is manufactured and measured, and good agreement is achieved between the simulation and measurement results.

The Laser Alloying Process of Ductile Cast Iron Surface with Titanium

The article presents the results of the laser alloying process of ductile cast iron EN-GJS 350-22 surface with titanium. The laser alloying process was conducted on 2 kW high power diode laser (HPDDL) Rofin Sinar DL02 with rectangular focus and uniform power density distribution in the focus axis. The laser alloying was conducted with constant laser beam power and processing speed with titanium powder feed rate variation. The tests of the produced surface layers included macrostructure and microstructure observations, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis, Vickers hardness, and solid particle erosion according to ASTM G76-04 standard. To assess the erosion mechanism, SEM observations of worn surfaces after erosive test were carried out. As a result of laser alloying of a ductile cast iron surface, the in situ metal-matrix composite structure was formed with TiC reinforcing particles. The microstructure change resulted in the increase of surface layers hardness and erosion resistance in comparison to the base material.

Laser surface alloying of ductile cast iron with Ti + 5% W mixture

The article presents results of the research on laser alloying of the ductile cast iron EN-GJS 350-22 substrate with the mixture of titanium powder with addition of 5 wt.% of tungsten. The aim of the process was to obtain surface layer with the in-situ composite structure. Laser alloying process was carried out using high power diode laser (HPDDL) with rectangular laser beam focus and uniform power density distribution in one axis of the beam focus (top-hat profile). The tests included determination of the influence of process parameters on the dimensions of the alloyed beads, metallographic macroscopic and microscopic observations, microhardness measurements of the laser alloyed layers and EDS chemical composition tests.

Large-area, tridimensional uniform microwave antenna for quantum sensing based on nitrogen-vacancy centers in diamond

For quantum sensing based on nitrogen-vacancy (NV) centers in diamond, microwave irradiation with uniform power density and large detection volume is necessary to achieve ultrahigh sensitivity. We demonstrate the fabrication of a double magnetic ring stereoscopic antenna used for the tridimensional uniform control of NV spin ensembles with a 4π mm2 × 2 mm large volume. Compared with those of traditional microwave antennas (copper wire and single-loop antenna), the sensitivity of the sensor can be improved 4.93 and 9.98 times, and the linearity of the lock-in signal can be increased by 2.04 and 1.11%, respectively. Moreover, the proposed antenna can suppress the thermal noise generated by itself and is amenable to three-dimensional (3D) integration.

Numerical analysis of the effect of electrode spacing on deposition rate profiles in a capacitively coupled plasma reactor

The effect of reactor dimension on deposition rate profiles is analyzed with a two-dimensional (2D) fluid simulation of a capacitively coupled plasma (CCP) reactor to deposit a hydrogenated silicon nitride (SiNxHy) film with a SiH4/NH3/N2/He gas mixture. We focus on the complex function of electrode spacing to reveal the physical relation between reactor geometry and deposition rate profiles. The simulation demonstrates that the localization of electron density is concentrated close to the powered electrode periphery for electrode spacing of 9 mm. However, the plasma distribution becomes bulk dominated with electrode spacing of 15 mm by relaxing the localization. As a result, the increase in the electrode spacing creates a more uniform electron power density profile, and the deposition rate profile of SiNxHy film changes from convex to concave in a radial direction. The change in the deposition rate profile is validated through comparison with the experimental observation, which agrees well with the simulation results with errors of less than 5%. The deposition rate profile with electrode spacing of 9 mm is very sensitive to the non-uniform gas density condition applied to the showerhead inlet. However, the deposition rate profile with electrode spacing of 15 mm is not sensitive to the inlet gas profile because of the increasing residence time. The increase of the electrode spacing promotes molecule–molecule gas phase reactions and consequently weakens the effect of the inlet boundary condition.

A microwave photonic generator of chaotic and noise signals

The transition to chaos in a microwave photonic generator has been experimentally studied for the first time, and the generated broadband chaotic microwave signal has been analyzed. The generator represented a ring circuit with the microwave tract containing a low-pass filter and a microwave amplifier. The optical tract comprised a fiber delay line. The possibility of generating chaotic oscillations with uniform spectral power density in a 3–8 GHz range is demonstrated.

Possible design of PBR for passive decay heat removal

Conditions for design parameters of above-ground and underground, prismatic high-temperature gas-cooled reactor (HTGR)s for passive decay heat removal based on fundamental heat transfer mechanisms were obtained in the previous works. In the present study, analogous conditions were obtained for pebble bed reactors by performing the same procedure using the model for heat transfer in porous media of COMSOL 4.3a software, and the results were compared. For the power density profile, several approximated distributions together with original one throughout the 10-MWt high-temperature gas-cooled reactor-test module (HTR-10) were used, and it was found that an HTR-10 with a uniform power density profile has the higher safety margin than those with other profiles. In other words, the safety features of a PBR can be enhanced by flattening the power density profile. We also found that a prismatic HTGR with a uniform power density profile throughout the core has a greater safety margin than a PBR with the same design characteristics. However, when the power density profile is not flattened during the operation, the PBR with the linear power density profile has more safety margin than the prismatic HTGR with the same design parameters and with the power density profile by cosine and Bessel functions.

Impact of power density profile on passive decay heat removal in prismatic HTGR

Reactor designs with passive safety features have been actively developed ever since the Fukushima Daiichi Nuclear Power Plant accident in 2011. In our previous works, we investigated the design of a small, prismatic HTGR for passive decay heat removal and the relations of parameters for successful decay heat removal. For the power density distribution of the HTGR, the Bessel function was used in the radial direction and the cosine function in the vertical direction, assuming a barrel-type cylindrical core. In practice, the power density distribution is usually flattened by introducing burnable poisons or control rods during operation to prevent non-uniform power production throughout the core. The power density profile might have an effect on the passive safety features of the HTGR. Therefore, the influence of a flat power distribution on the passive safety features of a prismatic HTGR was investigated in the present study. Results showed that flattening the power density profile allowed greater thermal power with the same safety performance without changing the reactor dimensions or calculation conditions. On the other hand, a same-power reactor could be designed with a smaller size without worsening its passive safety features, which is highly advantageous from an economical point of view. Hence, it was confirmed that reactor safety characteristics could be improved by implementing uniform power density in the design.

Investigation on cored-eutectic structure in Ni60/WC composite coatings fabricated by wide-band laser cladding

Ni60 composite coatings reinforced with WC particles were fabricated on the surface of Q550 steel using LDF4000-100 fiber laser device. The wide-band laser and circular beam laser used in laser cladding were obtained by optical lens. Microstructure, elemental distribution, phase constitution and wear properties of different composite coatings were investigated. The results showed that WC particles were partly dissolved under the effect of wide-band fiber laser irradiation. A special cored-eutectic structure was synthesized due to dissolution of WC particles. According to EDS and XRD results, the inside cores were confirmed as carbides of M23C6 enriched in Cr, W and Fe. These complex carbides were primarily separated out in the molten metal when solidification started. Eutectic structure composed of M23C6 carbides and γ-Ni(Fe) grew around carbides when cooling. Element content of Cr and W is lower at the bottom of cladding layer. In consequence, the eutectic structure formed in this region did not have inside carbides. The coatings made by circular laser beam were composed of dendritic matrix and interdendritic eutectic carbides, lacking of block carbides. Compared to coatings made by circular laser spot, the cored-eutectic structure formed in wide-band coatings had advantages of well-distribution and tight binding with matrix. The uniform power density and energy distribution and the weak liquid convection in molten pool lead to the unique microstructure evolution in composite coatings made by wide-band laser. Experiment results indicated the wear resistance and microhardness of composite coatings were both significantly improved.

Determination of conditions for the laser-induced intensification of mass transfer processes in the solid phase of metallic materials

The determination of conditions for laser-induced intensification of mass transfer processes in the solid phase of metallic materials was conducted. We studied the process of interdiffusion of Fe and Cu. A laser beam of uniform power density and a pulse frequency of 100, 1,000, and 5,000 Hz was used. The laser radiation was transformed into a uniform light spot with a diffractive optical element, which performed the required focusing. It was determined that for the generalized thermo-dynamic driving force to ensure the mass transfer intensification in non-equilibrium conditions, a necessary condition is the unsteady local deformation caused by laser action.

Synthesis of concentric ring antenna array for a wide isoflux pattern

AbstractThis research presents the synthesis of the concentric ring antenna arrays for a wide coverage pattern. The synthesis process is formulated as an optimization of the antenna excitations. Harmony search algorithm and particle swarm optimization are implemented for this optimization problem. The antenna array considers disk patches at the L‐band. First, the synthesis regards the behavior of the antenna array modeled by the cavity model. Second, the mutual coupling is included by using the full wave simulation. This synthesis could be very useful in satellites with terrestrial global coverage. The obtained antenna array provides a wide uniform power density and reduces considerably the hardware complexity for a satellite antenna system. Copyright © 2014 John Wiley & Sons, Ltd.

A RETRODIRECTIVE ARRAY WITH REDUCED SURFACE WAVES FOR WIRELESS POWER TRANSFER APPLICATIONS

A one-dimensional, dual frequency, active retrodirective array is proposed for wireless power transfer applications. Microstrip circular patch antennas with four shorting pins are used as array elements to suppress surface waves. The proposed design eliminates undesired coupling between array elements due to surface waves present in conventional microstrip antenna arrays in order to improve array performance. The antenna array uses circularly polarized microstrip elements with higher gain than conventional microstrip antennas. The proposed retrodirective array operates at 2.4 GHz for the interrogating signal and 5.8 GHz for the retransmitted signal, using up-converting mixers. The beam scanning inherent in retrodirective arrays ensures a constant power level available to the charging devices, regardless of their location within an angular sector over which retrodirectivity is achieved. A two-element experimental prototype provided uniform power density within a 60 ◦ angular sector. The Design procedure, simulation results and experimental measurements are presented.

Modified S-Band Satellite Antenna With Isoflux Pattern and Circularly Polarized Wide Beamwidth

A modified isoflux pattern antenna suitable for S-band satellite communication is introduced and investigated with respect to its beam pattern and axial ratios. For uniform coverage over the Earth's surface, an isoflux pattern antenna is required because of its uniform power density over a wide coverage area. A final optimization for the parameter values is carried out from the parametric studies of the antenna, and a simple analysis of the combination of horizontal dipoles and vertically attached top-hat elements is also carried out. The electrical performances of the proposed antenna are verified in terms of the reflection coefficients, radiation pattern, and axial ratios according to a wide beamwidth rather than at a fixed observation angle such as a 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> main beam direction.

Coupled analysis for new fuel design using UN and UC for SCWR

All-ceramic bi-material coated fuel pellet design is proposed and analyzed for thermal Super Critical Water Reactor (SCWR). Uranium mono nitride (UN) with Zirconium Carbide (ZrC) coating and Uranium mono carbide (UC) with Silicon Carbide (SiC) coating are analyzed. Carbide and nitride ceramic fuels offer the advantage of high thermal conductivity as compared to UO2. Use of coating can solve the problems of harder spectrum and reactive nature for UN and UC which arise when these fuels are used in light water thermal reactors. Larger heavy metal density of UN and UC can lead to equivalent or even larger values of heavy metal loading using coated pellet concept. Coating can give the extra advantage of working as yet another barrier against release of radioactive fission gases in accidental scenarios. Due to large coolant density variation along active height of fuel, coupled neutronics/thermal hydraulic analyses are performed using MCNP4c/SACoS coupled system. Design proposed by Shanghai Jiao Tong University (SJTU) for thermal SCWR is chosen to perform the calculations. Coupled analyses show that coated fuel pellets lead to more uniform radial power density which leads to smaller value of hot channel factor. A significant decrease in fuel centerline temperature is seen due to high thermal conductivity of carbide and nitride ceramic fuels. A staggering difference of more than 500 °C is seen between the maximum average centerline temperatures for UO2 and coated fuel pellets. Slightly smaller values of average clad surface temperature are obtained using coated fuel pellets as compared to UO2. A maximum coating temperature of less than 800 °C is observed. Effect of varying coating thickness is studied by performing analyses for different coating thickness values. Keeping the same fuel pin radius and pitch, increasing the thickness of coating materials can lead to increased value of thermal neutrons but will have a negative effect on the burnup due to smaller heavy metal loading. Reactivity coefficients, i.e. Doppler, coolant and moderator, show negative values. Considering the favorable neutronic and thermal hydraulic properties along with a potential increase in cycle length, all-ceramic bi-material coated fuel pellets can be a very good fuel option for SCWR.

High power supercontinuum generation in a nonlinear ytterbium-doped fiber amplifier

High power supercontinuum generation with 70 W average output power in a nonlinear ytterbium-doped fiber amplifier is demonstrated using all-normal dispersion, all-fiber master oscillator power amplifier configuration. The supercontinuum covers from 1064 nm to beyond 1700 nm with spectral flatness better than 12 dB and 67.3% optical to optical conversion efficiency. The almost uniform spectral power density across the whole continuum is more than 70 mW/nm and the nanosecond bursts output have an effective peak power of 82.7 kW.

Temperature-aware task scheduling algorithm for soft real-time multi-core systems

High temperature will affect the stability and performance of multi-core processors. A temperature-aware scheduling algorithm for soft real-time multi-core systems is proposed in this paper, namely LTCEDF (Low Thermal Contribution Early Deadline First). According to the core temperature and thread thermal contribution, LTCEDF performs thread migration and exchange to avoid thermal saturation and to keep temperature equilibrium among all the cores. The core temperature calculation method and the thread thermal contribution prediction method are presented. LTCEDF is simulated on ATMI simulator platform. Simulation results show that LTCEDF can not only minimize the thermal penalty, but also meet real-time guarantee. Moreover, it can create a more uniform power density map than other thermal-aware algorithms, and significantly reduce thread migration frequency.

Effect of Carbon Fillers on the Performance of a Composite Bipolar Plate for Fuel Cells

The bipolar plates were fabricated using compression molding of graphite (GR), carbon black (CB), multi-wall carbon nanotubes (MWNTs), carbon fibers (CF) and powder type epoxy resin. The electrical conductivity and flexural properties of the composites was increased with increasing the content of fibrous conducting fillers e.g., MWNTs and CF. However, when particulate fillers such as CB and GR were used, the electrical conductivity was increased, but the flexural properties deteriorated with increasing filler content up to certain content. A comparison was also made between the current-voltage (I-V) performances of fabricated composite bipolar plates and commercial graphite bipolar plate. The I-V characteristic in single cell test exhibited more uniform power density at both higher and lower current density and single cell performance increased with increasing the electrical conductivity.