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Numerical Analysis of Thermal Stress in Semi-Transparent Oxide Crystals Grown by Czochralski and EFG Methods
摘要： Crystal growth of oxides is generally difficult since large curvatures of the growth interface in these systems generate high thermal stress, dislocations and crystal cracking. Three-dimensional numerical modeling is applied to investigate thermal stress distribution in sapphire and langatate La3Ta0.5Ga5.5O14 (LGT) semi-transparent crystals grown by Czochralski (Cz) and Edge-defined Film-fed Growth (EFG) techniques. The analysis of thermal stress distribution in a sapphire ingot grown in a Czochralski furnace shows high von Mises stresses distributed almost symmetrically on large areas in the crystal. Thermal stress computations for piezoelectric langatate crystals grown in a Czochralski configuration show non-symmetrical von Mises distribution with higher stress on one side of the ingot. These numerical results are in agreement with experimental results showing non-symmetrical cracking at the outer surface of the crystal. 3D modeling of multi-die EFG growth of white sapphire ribbons shows that the von Mises stress is almost constant when the number of ribbons is increased from two to ten. Two models are applied to simulate the internal radiative heat transfer in the sapphire crystals: P1 approximation and the Rosseland radiation model. Numerical results show that applying Rosseland formula introduces significant errors in temperature field calculations especially in the case of the EFG configuration.
关键词： computer simulation,Czochralski,sapphire,single crystal growth,stresses
更新于2025-09-23 15:22:29
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An analysis of low flow for solar thermal system for water heating
摘要： The mass flow rate in the collector loop of a solar domestic hot water system (SDHW) affects its thermal performance. The initial investment and the operation cost are also affected by the selection of the primary flow. Common design rules state a standard specific flow rate of 50 l/hm2 for most collector models. However, the emergence of electronically commuted motors recommends reviewing the interest of the low flow alternative (7–14 l/hm2) for solar thermal systems. In this paper, the thermal performance of a typical serpentine collector has been measured for different mass flow rates. The resulting performance curves and associated measurement uncertainty bands show only a moderate improvement in performance as the flow rate increases. Once the collector thermal behaviour has been characterized, the whole system is modelled, and the initial investment and operating cost are calculated for two design options: high flow (80 l/hm2) and low flow (20 l/hm2). As expected, the solar fraction is slightly higher for the high flow system (4.6% higher) and the number of hours of operation is lower for this system (4.4% less hours of operation). Considering the lower investment cost of the low flow system, the best thermal behaviour of the high flow system requires near 18 years to amortize the largest investment. If other considerations like embodied energy are accounted for, the common practice in designing SDHW systems should promote low flow.
关键词： Solar thermal simulation,Flat plate collector,Low flow,Variable flow
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 38th International Conference on Electronics and Nanotechnology (ELNANO) - Kiev (2018.4.24-2018.4.26)] 2018 IEEE 38th International Conference on Electronics and Nanotechnology (ELNANO) - Simulated Phantom Projections for Reconstruction Quality Control in Digital Tomosynthesis
摘要： IMASIM software was used to generate sets of X-ray projections for quality control in digital tomosynthesis. Corresponding projections of a polymethylmethacrylate(PMMA) phantom with the same size were taken using x-ray tomosynthesis imaging equipment. A specially designed fiduciary marker bead phantom was used to measure the relative positions of imaging system elements. A good correspondence was found between real and simulated projections and reconstructed slices. The ability to create simulated projections with predefined imperfections gives valuable benefits to analysis of overall tomosynthesis performance.
关键词： X-ray applications,digital X-ray tomosynthesis,quality control,biomedical imaging,numerical simulation
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Krakow (2018.10.16-2018.10.18)] 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - A Fast Way to Get Sensitivity Map of Wire-Mesh
摘要： This paper presents a new method for obtaining the sensitivity map of a wire-mesh sensor (WMS) based on the Maxwell-Wagner effect. The sensitivity map is crucial for the accuracy of electrical capacitance tomography (ECT) in industrial process monitoring. Traditional methods for sensitivity map calculation are complex and time-consuming. The proposed method simplifies this by using a simulation approach that models the WMS as a two-phase flow sensor. The results show that the new sensitivity map improves the imaging quality and reduces the computational time compared to conventional methods. This method is validated through simulations and experiments, demonstrating its effectiveness for practical applications in multiphase flow measurement.
关键词： wire-mesh tomography,sensitivity map,simulation
更新于2025-09-23 15:22:29
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A Monte Carlo based dosimetric characterization of Esteya <sup>?</sup> , an electronic surface brachytherapy unit
摘要： The purpose of this work is threefold: First, to obtain the phase-space of an electronic brachytherapy (eBT) system designed for surface skin treatments. Second, to explore the use of some efficiency enhancing (EFEN) strategies in the determination of the phase-space. Third, to use the phase-space previously obtained to perform a dosimetric characterization of the Esteya eBT system. Methods: The Monte Carlo study of the 69.5 kVp x-ray beam of the Esteya? unit (Elekta Brachytherapy, Veenendaal, The Netherlands) was performed with PENELOPE2014. The EFEN strategies included the use of variance reduction techniques and mixed Class II simulations, where transport parameters were fine-tuned. Four source models were studied varying the most relevant parameters characterizing the electron beam impinging the target: the energy spectrum (mono-energetic or Gaussian shaped), and the electron distribution over the focal spot (uniform or Gaussian shaped). Phase-spaces obtained were analyzed to detect differences in the calculated data due to the EFEN strategy or the source configuration. Depth dose curves and absorbed dose profiles were obtained for each source model and compared to experimental data previously published. Results: In our EFEN strategy, the interaction forcing variance reduction (VRIF) technique increases efficiency by a factor ~ 20. Tailoring the transport parameters values (C1 and C2) does not increase the efficiency in a significant way. Applying a universal cutoff energy EABS of 10 keV saves 84% of CPU time whilst showing negligible impact on the calculated results. Disabling the electron transport by imposing an electron energy cutoff of 70 keV (except for the target) saves an extra 8% (losing in the process 1.2% of the photons). The Gaussian energy source (FWHM = 10%, centered at the nominal kVp, homogeneous electron distribution) shows characteristic K-lines in its energy spectrum, not observed experimentally. The average photon energy using an ideal source (mono-energetic, homogeneous electron distribution) was 36.19 ± 0.09 keV, in agreement with the published measured data of 36.2 ± 0.2 keV. The use of a Gaussian-distributed electron source (mono-energetic) increases the penumbra by 50%, which is closer to the measurement results. The maximum discrepancy of the calculated percent depth dose with the corresponding measured values is 4.5% (at the phantom surface, less than 2 % beyond 1 mm depth) and 5% (for the 80% of the field) in the dose profile. Our results agree with the findings published by other authors and are consistent within the expected Type A and B uncertainties. Conclusions: Our results agree with the published measurement results within the reported uncertainties. The observed differences in PDD, dose profiles and photon spectrum come from three main sources of uncertainty: inter-machine variations, measurements and Monte Carlo calculations. It has been observed that a mono-energetic source with a Gaussian electron distribution over the focal spot is a suitable choice to reproduce the experimental data.
关键词： simulation efficiency,Monte Carlo simulation,electronic brachytherapy,surface treatment,dosimetry,x-ray source
更新于2025-09-23 15:21:21
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Evaluation method for the performance of light screen array measurement system based on semi-physical simulation
摘要： The paper presents a method to evaluate the performance of light screen array measurement system (LSA for short) objectively and scienti?cally. We put forward the scheme of semi-physical veri?cation platform based on arbitrary waveform generator (AWG), and this instrument is used as a substitute for light screen detector in the LSA. according to some main characteristics of dynamic signal, the waveform ?les of two simulation signals with a certain time interval are compiled and created through con?guring some options through a signal waveform edition software. Furthermore, these waveform ?les are downloaded into the AWG to generate two channel simulation signals. Then, the time interval of these two signals can be measured in the signal acquisition & processing module of LSA. Finally, we can compare the di?erence between true values and measured results. Through experiment and analysis, the proposed method can meet the requirement of performance evaluation on the LSA, and it is superior to the other previous methods.
关键词： Semi-physical simulation,Noise environment,Waveform modeling and editing,Photoelectric measurement,Dynamic signal generation
更新于2025-09-23 15:21:21
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Effect of crucible and crystal rotations on the solute distribution in large size sapphire crystals during Czochralski growth
摘要： In this study, the ?ow, temperature and solute concentration ?elds in the melt during the CZ growth process are numerically investigated. The results show that the magnitude and distribution of the solute concentration in the melt is strongly affected by the convective ?ow and thermal distribution. The maximum solute concentration always occurs at the crucible sidewall where the maximum temperature in the melt is found and the solute concentration at the crystal-melt interface increases from the triple point to the centerline. Heat transport from the side crucible wall towards the crystal-melt interface is enhanced by the crucible rotation. The level of the solute concentration inside the melt is reduced due to the lowering of the maximum temperature at the crucible wall. As a consequence, the distribution of the solute concentration along the crystal-melt interface becomes smaller and more uniform as the crucible rotation rate increases. However, after the crucible rotation rate becomes large enough, the maximum solute concentration and the solute concentration along the crystal-melt interface start to increase. Heat transport inside the melt is also affected by the crystal rotation. The centrifugal force induced by the crystal rotation generates a vortex below the crystal-melt interface. This vortex gets larger and stronger as the crystal rotation rate increases. In the smaller crystal rotation rate regime, this vortex is very small, suppressing the solute concentration at the crystal-melt interface. Therefore, the solute concentration along the crystal-melt interface becomes less when the crystal rotation rate is higher, although there is an increase in the maximum solute concentration in the melt due to the higher maximum temperature. In the higher crystal rotation rate regime, there is a reduction in the convexity of the crystal-melt interface due to enhancement of heat transport from the bottom wall of the crucible by vortex motion under the crystal-melt interface. Therefore, there is a switch to an increase in the transport of solute impurities into the crystal-melt interface. Hence, the solute concentration along the crystal-melt interface increases as the crystal rotation rate increases. However, with a further increase in the crystal rotation rate, as the shape of the crystal-melt interface changes becoming concave towards the melt, the solute concentration along the crystal-melt interface decreases because the maximum temperature is signi?cantly reduced. In this study, both counter- and iso-rotations are considered. The results of a comparison of the cases of iso- and counter-crystal rotation show that the lowest and most uniform solute distribution along the crystal-melt interface is achieved when there is no crystal rotation and the crucible rotation rate is ?xed at 1 rpm. In other words, the lowest and most uniform solute concentration can be achieved with the only crucible rotation.
关键词： Solute concentration,Czochralski method,Sapphire,Numerical simulation,Crucible and crystal rotations
更新于2025-09-23 15:21:21
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Characteristics of GeSn-based multiple quantum well heterojunction phototransistors: a simulation-based analysis
摘要： Introduction of multiple quantum wells (MQWs) is an efficient way to enhance the light absorption capability in phototransistors. Direct band gap Ge1?xSnx alloy (x?>?0.08) having large absorption coefficient is an attractive material for heterojunction phototransistors (HPTs) compatible with CMOS platform. In this work, simulations are employed to obtain current gain, responsivity and collector current characteristics of Ge/GeSn/Ge HPTs with incorporation of MQWs (Ge0.87Sn0.13/Ge0.83Sn0.17) in the base region. The performances of bulk, single quantum well and MQW HPT structures are examined and compared. Best performance is shown by HPTs having MQW structure over a wide range of base emitter voltage.
关键词： simulation,current gain,heterojunction phototransistors,responsivity,GeSn,multiple quantum wells
更新于2025-09-23 15:21:21
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Design guidelines for high sensitivity ZnO nanowire gas sensors with Schottky contact
摘要： Zinc oxide nanowire (ZnO NW) gas sensor with single Schottky contact is capable of sensitive detection of gas molecules. In this study, we investigate the effect of design factors such as nanowire defect density, diameter, and length on the gas sensitivity using 3-D numerical simulation. The sensor with lower defect density or smaller NW diameter exhibits improved gas sensitivity, while length does not have an impact when not considering the external environment such as background gases and binding probability. Lower defect density causes low electron density within the NW in air environment, and the change in electron density due to gas adsorption is intensified, thus improving gas sensitivity. As the NW diameter decreases, the change in the electrical conductivity due to gas molecules is greatly increased due to an increase in the ratio of the depletion area to the entire NW area. In contrast, the nanowire length does not impact the gas sensitivity because the change in the electron density is independent of the length. These results are helpful to understand the sensing mechanism and provide design guidelines to maximize the sensitivity.
关键词： Zinc oxide,Gas sensitivity,Nanowire,Numerical simulation,Gas sensor
更新于2025-09-23 15:21:21
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[IEEE 2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - Reykjavik, Iceland (2018.8.8-2018.8.10)] 2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - Low-Cost Simulation-Driven Design of Broadband Rectifiers for Ambient RF Energy Harvesting
摘要： A steady growth of ambient RF energy density associated with a rapid increase of the number of broadcasting devices stimulates the research on broadband harvesting circuits. Such circuits can be used as energy sources for low-power sensors or Internet-of-Things devices. On the other hand, dedicated design techniques for rectifiers are lacking which results in poor performance of existing circuits. Also, their design cost is high because it involves hybrid electromagnetic (EM) and harmonic balance (HB) simulations. In this work, we propose a novel design procedure for low-cost design of broadband rectifiers. The core component of the approach is a novel equivalent-circuit-based low-fidelity model which does not involve harmonic balance (HB) simulations. The model consists of a matching circuit loaded with the RF-to-DC converter block represented using the S-parameter matrix. The latter is obtained from a single HB simulation of the converter circuit. Inaccuracy of the model is reduced using appropriate correction techniques. At the first stage of the design process, the proposed model is optimized for minimization of the in-band reflection. At the second stage, a hybrid HB-EM-based tuning oriented towards maximization of the structure efficiency is carried out. The proposed approach is demonstrated using a novel broadband rectifier operating within 0.5 GHz to 3.5 GHz band. Numerical cost of the method is 80% lower compared to direct EM-HB- based optimization of the rectifier circuit.
关键词： broadband rectifiers,constrained optimization,simulation-driven design,surrogate-based optimization,equivalent circuit model
更新于2025-09-23 15:21:21