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用于激光颗粒测试技术的非球形颗粒的椭圆衍射模型 总被引:4,自引:0,他引:4
激光颗粒大小测试的结果与颗粒形状密切相关。通过对椭圆衍射谱的研究,提出在激光粒度分析中以椭圆谱代替球形颗粒谱。计算机模拟计算与对金刚砂实测的结果表明椭圆衍射模型可以有效地抑制粒度反演结果的展宽,更准确地获得非球形颗粒群的粒度分布 相似文献
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多波长散射光通量法测颗粒尺寸分布的实验研究 总被引:2,自引:0,他引:2
基于经典Mie光散射理论,提出一种改进的多波长散射光通量测量颗粒粒尺寸的方法,对标准颗粒及实际样品的实验研究表明,该方法不仅能测量颗粒的平均直径,还能给出尺寸分布。 相似文献
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铝硅合金表面纳米颗粒的原子力显微镜观察 总被引:1,自引:0,他引:1
利用原子力显微镜首次观察到200℃磁控溅射铝硅合金表面存在纳米颗粒,经测量,此纳米颗粒直径约20nm、高1nm。根据此纳米颗粒的分布,讨论了磁控溅射薄的生长机理,同时,还讨论了此纳米颗粒对半导体工艺的影响。 相似文献
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烟雾场中存在多种悬浮颗粒,这些颗粒尺寸和分布概率的测量对烟雾剂研制和性能评价十分重要但由于烟雾场自身的特殊性,测量不能沿用目前流行的技术和方法,本文阐述一种基于光学成象原理,运用CCD摄象技术和计算机信息处理,获取场中悬浮颗粒各种数据信息的方法。 相似文献
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侧向送粉激光熔覆粉末温升模型及实验研究 总被引:4,自引:0,他引:4
建立了侧向送粉激光熔覆粉末颗粒温升的数学模型,该模型可以考虑激光束的功率分布。推导了考虑激光束直径大于粉斑直径和小于粉斑直径两种情况下,粉末颗粒在光束辐照下的温升与其在光束下运动时间的关系式。通过算例,给出了在不同激光功率下粉末颗粒的温升随其与激光束相互作用时间的关系曲线以及不同颗粒直径条件下粉末颗粒温度随相互作用时间的关系曲线。采用微距摄影技术对粉末颗粒到达熔池表面的状态进行实验观测,并采用图像分割技术中的迭代阈值选取方法,对所获得的灰度图进行处理从而得到了粉末颗粒到达熔池的温度。计算结果与实验分析获得了相同的结论,从而验证了模型的正确性。 相似文献
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消光起伏光谱法高浓度效应的模拟计算 总被引:3,自引:0,他引:3
消光起伏光谱法(TFS)是最近发展起来的颗粒测量技术,它可以同时测量颗粒粒径分布和浓度,并可用来进行在线、实时测量。在频率域内对透过率起伏信号进行频谱分析,信号分析系统采用品质因数为0.707的二阶低通滤波器。通过模拟计算得到有关单层与多层颗粒系统的归一化差值函数经验表达式,由此分析颗粒系统的高浓度效应(包括颗粒交叠效应和层结构)对消光起伏光谱的影响。结果表明,高浓度效应与颗粒系统的浓度、层数及光束-颗粒直径比Λ都有关系,它对消光起伏光谱特征函数的影响主要体现在频谱移动和阶高变化两个方面:一般来讲,消光起伏光谱的频率响应主要受颗粒交叠响应的影响,表现为向低频区移动;而消光起伏光谱特征函数的阶高则同时受层结构和颗粒交叠效应影响。 相似文献
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在激光衍射式粒度分析技术中,准确地获得被测颗粒群的衍射谱是分析颗粒群尺寸分布的基础,从颗粒之间直接透过的光会聚于光电探测器的中心,产生强烈的多次反射。对信号的测量产生很大的影响,甚至会导致测量的失败,对此有两种解决的办法:或在光电探测器的中心打一孔让会聚光通过;或用强吸收材料贴在光电光探测器的中心来减少会聚 相似文献
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We have extended the concept of flip-chip technology, which is widely used in IC packaging, to the packaging of three-dimensional (3-D) integrated power electronics modules (IPEMs). We call this new approach flip-chip on flex IPEM (FCOF-IPEM), because the power devices are flip-chip bonded to a flexible substrate with control circuits. We have developed a novel triple-stacked solder bump metallurgy for improved and reliable device interconnections. In this multilayer structure, we have carefully selected packaging materials that distribute the thermo-mechanical stresses caused by mismatching coefficients of thermal expansion (CTEs) among silicon chips and substrates. We have demonstrated the feasibility of this packaging approach by constructing modules with two insulated gate bipolar transistors (IGBTs), two diodes, and a simple gate driver circuit. Fabricated FCOF-IPEMs have been successfully tested at power levels up to 10 kW. This paper presents the materials and reliability issues in the package design along with electrical, mechanical, and thermal test results for a packaged IPEM 相似文献
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Measurements of impulsive noise in the universal mobile telecommunications system (UMTS) electromagnetic environment in urban areas have been conducted and its effect on the UMTS system is analyzed. An impulsive noise-measurement system for the UMTS frequency band has been designed and built, which meets and improves the main features of classical equipments used to measure noise, offering inphase and quadrature outputs simultaneously. This measurement system was carefully calibrated before a measurement campaign was conducted in an urban environment to get impulsive noise statistics. Results show that noise pulses may have high power, long duration, and high repetition rate, so the performance of UMTS could be significantly reduced. 相似文献
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Terrence Mak Author Vitae Pete Sedcole Author Vitae 《Integration, the VLSI Journal》2010,43(2):188-201
On-FPGA communication is becoming more problematic as the long interconnection performance is deteriorating in technology scaling. In this paper, we address this issue by proposing a novel wave-pipelined signaling scheme to achieve substantial throughput improvement in FPGAs. A new analytical model capturing the electrical characteristics in FPGA interconnects is presented. Based on the model, throughput and power consumption of a wave-pipelined link have been derived analytically and compared to the conventional synchronous links. Two circuit designs are proposed to realize wave-pipelined link using FPGA fabrics. The proposed approaches are also compared with conventional synchronous and asynchronous pipelining techniques. It is shown that the wave-pipelined approach can achieve up to 5.7 times improvement in throughput and 13% improvement in power consumption versus conventional delay-based on-chip communication schemes. Also, trade-offs between power, throughput and area consumption between the proposed and conventional designs are studied. The wave-pipelining approach provides a new alternative for on-FPGA communications and can potentially become a promising solution to mitigate the future interconnect scaling challenge. 相似文献
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Three-dimensional flip-chip on flex (FCOF) integrated power electronics modules (IPEMs) have been fabricated for high-density power applications. In this FCOF-IPEM structure, solder-bumped devices were flip-soldered to a flexible substrate with electrical circuits etched on both sides. One side of the flex provides interconnection to power devices while the other is used to construct a simple gate-drive circuit; via holes through the flex integrate the power stage and gate-drive together. Solder-bumped MOSFET devices were obtained by a metallization processing and were used in the FCOF power module construction to improve thermal performance, power density, and integration. With this packaging approach, the multiple solder bumps, instead of the thin, long bonding wires were utilized to connect the power devices to the flex substrate and to improve heat dissipation, lower parasitic oscillations, and reduce package size. Reliability of solder joints has been dealt with through selection of materials, such as use of flexible substrates and underfill encapsulation, and design of joint shape for lower thermomechanical stresses. A comparative study of continuous switching test results have shown that the FCOF-IPEMs have better electrical performance than commercial wire bonded power modules. 相似文献
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In this paper, a power allocation in multibeam satellite (MBS) communication based on heuristic particle swarm optimization (PSO) is proposed. The PSO algorithm is evocated to solve the problem of power allocation in the multiple narrow spotbeams aiming to provide the minimum signal-to-noise plus interference ratio (SNIR) required by Earth station users to establish reliable communication. In the developed model it is considered the multibeam interference and the different channel conditions of each beam by rain attenuation. The numerical results have been generated taking into account different sky situations, including clear and rainy scenarios; such results have revealed the viability and accuracy of the PSO algorithm deployment in solving the power allocation problem. In addition, with the proposed scheme it is observed the decrement of transmitted power for non-rainy beams with guarantee of the minimum SNIR at the Earth receivers input, while increase the power availability to the rainy beams; as a consequence, the overall energy efficiency of the MBS system has been improved substantially. Moreover, the convergence of the proposed heuristic PSO-based algorithm is discussed while such heuristic approach comes with computational complexity reduction when compared with others efficient power allocation schemes. 相似文献
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Gholamreza Karimi Ali Lotfi 《AEUE-International Journal of Electronics and Communications》2013,67(8):723-728
In this paper, a novel pre-distorter is presented using the particle swarm optimization (PSO) for an RF power amplifier linearization has been presented. We used the PSO in order to design of an efficient pre-distorter for the linearization of the output of an RF power amplifier by using the output data of the proposed power amplifier. The PSO is implemented to estimate and optimize the coefficient parameters of the work function in the proposed pre-distorter block diagram. The proposed method using PSO is most efficient because this approach is independent of the output of the power amplifier. The proposed method has been simulated with two-tone input signal and output power spectrum has been compared, where the obtained adjacent channel leakage ration (ACLR) is better than 50 dBc for both channels. Therefore, a quite significant improvement in linearity is achieved. 相似文献
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Yu. A. Nemlikher I. A. Strukov 《Journal of Communications Technology and Electronics》2009,54(2):218-224
A new approach to the optimization of the transfer characteristics of resistive frequency converters is studied. In this approach, with allowance for the requirement of practicality, the required power of a local oscillator is determined for the assigned conductance of a signal generator. As has been demonstrated, this is also the necessary condition that ensures the zero sensitivity of conversion loss to small fluctuations in the power of a local oscillator. The formulas required for calculations have been obtained. 相似文献
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J. Xu X. Gao Y. X. Jie H. Q. Liu B. N. Wan Y. Y. Wei C. Cheng Z. J. Xu 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(8):1163-1173
A successful experiment on lower hybrid wave (LHW) and ion Bernstein wave (IBW) synergy has been carried out in the HT-7 superconducting tokamak. With 560KW of LHW heating power and 160 KW of IBW heating power, during the synergy of the LHW and IBW experiment we achieved an improved plasma: the electron density increased and peaked, the soft X intensity increased too. A five-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer was used to measure the electron density profile. The particle diffusion coefficient was studied for the experiment, and the result compared with the heat diffusion coefficient. With the same injected LHW and IBW power, high electron density ne can deduce the electron pulse propagation and the particle diffusion. 相似文献
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Hanifa Nabuuma Emad Alsusa Mohammed W. Baidas 《International Journal of Communication Systems》2019,32(7)
IEEE 802.11ah is a WiFi standard developed to address requirements associated with the heterogeneous nature of the Internet of Things. It uses the sub‐1 GHz bands to enable long‐range transmissions for low‐power devices. However, long‐range coverage exacerbates the hidden node problem. To mitigate this problem, sectorization and grouping have been proposed by the standard. In this paper, hierarchical clustering and a modified Welsh‐Powell algorithm are combined to create hidden node‐free groups in a sectorized wireless local area network. An analytical model is developed for a deterministic backoff technique that uses association identifiers to set the backoff in order to eliminate collisions. The performance of the deterministic backoff technique is compared with that of existing schemes. Our results show that this approach results in higher throughput and lower latency than other deterministic backoff techniques. 相似文献