气动加热下高温陶瓷材料的红外辐射机理与特性

从分析材料内部热辐射与导热耦合传热温度场、表面反射及折射之间的内在关系出发,建立了气动加热下高温陶瓷材料的红外辐射模型.采用控制容积法结合蒙特卡罗法和谱带模型,数值模拟了红外辐射能在材料内部的传递及出射过程.引入介质影响因子,分析了材料的红外辐射机理和外部气动热流对材料红外辐射特性的影响.结果表明,高温陶瓷材料内部热辐射的光谱选择性与温度场的耦合,导致高温陶瓷材料的红外发射率随气动热流变化而变化.由于陶瓷材料在紫外和中远红外谱带范围对辐射的吸收非常强,而在近红外和可见光谱带范围对辐射吸收较弱,随气动热流密度增大,对陶瓷材料表面红外辐射产生贡献的内部热辐射区域增大,但材料的红外发射率降低.     

阻容元件对音频放大器的影响及其选用

阻容元件是在音响设备中使用量最大的无源器件,近年来国内的音响制造商,在设计音源（CD或DVD）、功率放大器的过程中,非常重视集成块（IC）、晶体三极管、场效应管及电子管等有源器件的选用,在电路设计、产品工艺等方面取得了长足的进步。但在高附加值的HI-END级音响产品领域,与欧美国家存在较大的差距。原因之一是对电阻、电容等无源器件的选用重视不够。为了提高音响设备的重放效果,通过对阻容元件的分析、研究,采用同一套音响设备、不同的阻容元件进行比较测试,发现阻容元件对音响设备的影响不容小视,合理选择阻容元件可提高音响设备的性能指标和重放效果。     

不同加热条件下加热电离层的效应研究

利用电离层欧姆加热的理论模型和数值分析模型,根据数值模拟结果,对高频电波加热电离层的一级空间效应(主要是电子密度和电子温度的改变)进行定量分析,给出在不同地域(高纬区和中低纬区)、不同加热功率、不同加热频率(包括过密和欠密情况)和不同高度范围内,地基高频无线电波加热电离层引起的电离层主要参量的时空演化规律,以获取加热条件或参数的改变对不同区域电离层的加热效果.并结合国外相近纬度区、相近加热参数条件下的实验结果进行对比分析,给出了初步结论.     

碳化硅加热元件的电性能和使用

本文介绍碳化硅加热元件的电特性、表面负荷以及工作气氛对它的影响，并对它设计和使用要点举例予以说明。     

不同环境与加热路径下的微波加热岩石的数值研究

硬质岩隧道开挖是一个难题,文章通过采用有限元软件建立玄武岩的微波加热模型,分析了岩石外界环境温度、换热系数、照射时间以及加热路径对微波照射岩石的影响。计算结果发现降低环境温度、增大换热系数两者实质相似,均是使得岩石表面温度降低较大,在岩石内形成较大温度梯度,从而产生温度应力,引起岩石破坏。延长微波照射时间虽然可以提高温度应力,但破坏效果与照射时间并未呈现正比关系。通过改变微波加热路径,在总时间不变的情况下,在加热中途增加一个自然冷却过程,可以显著提高微波照射效果。     

SH系列乳白石英远红外加热元件中气泡作用的分析

本文通过对SH系列乳白石英远红外加热元件中气泡作用的分析,阐述了这种远红外加热元件的节电机理。     

SiC高温快速退火加热系统设计与研究

SiC芯片注入激活设备具有高温特点,传统的加热方式通常采用感应式和电阻式加热,采用电阻加热方式具有温度精度高、能耗小等优势。根据SiC高温快速退火设备的特点,深入结合工艺需求,通过采用正向设计手段,对功率计算、材料选型、加热器结构设计、电学参数分配,以及温控系统设计方面进行研究。     

开口式微波加热器的研究

应用时域有限差分法(FDTD)分析和计算了一种开口式同轴加热装置。同时讨论和计算了为防止微波泄漏而设计在腔体外围的扼流槽的作用。测量结果与计算结果有相当高的一致性。表明这种装置可以在中心处产生高温,而在设计相关的微波装置时,使用时域有限差分法又是十分有效的。     

微波高温加热真空系统的研制

在微波加热原理的基础上,根据具体的实验要求,介绍了一套自制的多模谐振腔微波高温加热真空系统。在该真空系统上进行了温度场测量;碳毡和碳化硅的微波加热试验;碳毡的气相致密化与碳化钨陶瓷的烧结试验。结果表明:该微波加热系统电场主要聚焦在中心区域,而且均匀分布;在气氛保护下,碳化硅的加热温度在20m in内达到1700℃,碳化钨的烧结致密度达到96%以上,在90小时内,碳毡的密度可达1.70g/cm3。     

军工电子产品元器件选用使用的误区及对策研究

元器件的可靠性决定着军工电子产品的可靠性,所以针对工作中的实际经验对实际选用使用中存在的误区进行了归纳分析,并提出了采取的对策措施。     

10kV配网导线的选型原则及现状分析

本文主要围绕10kV配网导线的选型原则进行阐述,在不断融入现代化配网技术的基础上,优化整个方案设计,更好的实现在10kV配网导线的综合功能,受到更好的效果.     

Finite element analysis of the temperature field in a vertical MOCVD reactor by induction heating

The temperature field in the vertical metalorganic chemical vapor deposition (MOCVD) reactor chamber used for the growth of GaN materials is studied using the finite element analysis method (FEM). The effects of the relative position between the coils and the middle section of the susceptor, the radius of the coil, and the height of the susceptor on heating condition are analyzed. All simulation results indicate that the highest heating efficiency can be obtained under the conditions that the coil distributes symmetrically in the middle section of the susceptor and the ratio of the height of the susceptor to that of the coil is three-quarters. Furthermore, the heating efficiency is inversely proportional to the radius of the coil.     

立式MOCVD反应室感应加热温度场的有限元分析*

The temperature field in the vertical metalorganic chemical vapor deposition （MOCVD） reactor chamber used for the growth of GaN materials is studied using the finite element analysis method （FEM）. The effects of the relative position between the coils and the middle section of the susceptor, the radius of the coil, and the height of the susceptor on heating condition are analyzed. All simulation results indicate that the highest heating efficiency can be obtained under the conditions that the coil distributes symmetrically in the middle section of the susceptor and the ratio of the height of the susceptor to that of the coil is three-quarters. Furthermore, the heating efficiency is inversely proportional to the radius of the coil.     

Game‐theoretic modeling and analysis of relay selection in cooperative wireless networks

In this paper, distributed single relay selection in cooperative wireless networks is modeled as a Chinese restaurant game (CRG). Specifically, the CRG is used to model strategic relay selection decisions of source nodes, taking into account negative network externality due to the potential sharing of relay nodes among source nodes. Two cases are studied as follows: (i) perfect relay transmit power (RTP) knowledge and (ii) imperfect RTP knowledge. Under the first case, a distributed relay selection algorithm is proposed and shown to converge to a Nash equilibrium grouping. Under the second case, a reinforcement learning algorithm is proposed and combined with the distributed relay selection algorithm to allow network nodes to select rate‐maximizing relays. Simulation results verify the efficiency of the proposed distributed relay selection algorithm when compared with other relay selection schemes and demonstrate that it yields a network sum‐rate that is comparable with that of centralized relay selection. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance of selective space‐time coding and selection diversity under perfect and imperfect CSI

Selective space‐time coding and selection diversity can be viewed as practical means to reduce the implementation complexity of multiple‐input multiple‐output (MIMO) systems while still taking benefit of the use of multiple antennas. In this paper, we evaluate the performance of selective space‐time block coding (selective‐STBC) and antenna selection diversity, and analyze the performance of both techniques under perfect and imperfect channel state information (CSI) available at both ends of the transmission link. Our performance analysis reveals that, under perfect or imperfect CSI and ideal feedback channel, selective‐STBC yields a loss in selection diversity gains and that selecting just a single antenna at the transmitter side is the best transmission strategy. We also show that selective‐STBC and antenna selection diversity have different behaviors when the feedback channel is imperfect. Indeed, it is shown that selection diversity outperforms selective‐STBC when the feedback channel is of high quality, while selective‐STBC yields better performance when the feedback channel is of low quality. Copyright © 2008 John Wiley & Sons, Ltd.     

Mechanical and electrical characterisation of Au wire interconnects in electronic packages under the combined vibration and thermal testing conditions

This paper concerns the reliability of thermosonically bonded 25 μm Au wires in the combined high temperature with vibration conditions, under which the tests have been carried out on wire-bonded 48-pin Dual-in-Line (DIL) High Temperature Co-fired Ceramic (HTCC) electronic packages. Mechanical, optical and electrical analysis has been undertaken in order to identify the failure mechanisms of bonded wires due to the combined testing. The results indicated a decrease in the electrical resistance after a few hours of testing as a result of the annealing process of the Au wire during testing. In general, ball shear and wire pull strength levels remained high after testing, showing no significant deterioration due to the tests under the combined high temperature and vibration conditions. However, a trend of the variation in the strength values is identified with respect to the combined conditions for all wire-bonded packages, which may be summarised as: (i) increase of the testing temperature has led to a decrease of both the shear and pull strength of the wire bonds; (ii) the mechanical behaviour of the wires is affected due to crystallisation that leads to material softening and consequently the deformation of wire.     

高温阻抗测控系统

介绍了高温（１２５０℃）下材料及片状元件阻抗（电容、电阻、电感电抗、损耗角正切）温度频率特性测控系统的硬件构成以及测控软件。采用铂金作为导线,实现了高温下多吕阻抗参数的精确测试,而且可以设置多段升温曲线。该套系统对于高居里温度的铁电材料及其他材料在高温下性能的研究具有重要价值。     

长脉冲激光能量时空分布对金属热作用的影响

为研究激光能量的时空分布对金属基体材料热作用效果的影响,建立了空间轴对称有限元计算模型.在平均功率相等和考虑吸收率随温度变化的前提下,分别模拟了平均功率相等的连续激光和长脉冲激光(脉宽为1 ms,脉冲频率分别为25、50、100和250 Hz)与Al板作用过程中气化前的热作用,并利用热焓法处理了固-液相变过程,对比了能量的时空分布不同的激光热作用效果的影响.结果表明:由于基体材料的吸收率同温度之间相互促进的关系,在上述前提下,热作用效果随重复频率的减小显著增加,并且金属吸收率的温度相关性对温升过程庞大影响.     

Symbol error probability of mmWave communications with transmit antenna selection and RISs under the impacts of hardware impairments

In practice, hardware impairments (HIs) often exist in wireless devices, especially in low-cost device systems. However, previous reports usually ignored HIs due to the computational complexity in mathematical derivations, particularly in millimeter-wave (mmWave) communications. This article proposes the usage of transmit antenna selection (TAS) and multiple reconfigurable intelligent surfaces (RISs) to address HIs in mmWave communications. In particular, TAS is utilized at the source to increase the received signal power at the destination and reduce the effects of HIs. Multiple channel gains from RISs are combined with the classical source-destination channel gain at the destination. The symbol error probability (SEP) expression of the mmWave communications with TAS and RISs under the effects of HIs (shortened as the TAS-RISs-HIs communications) is formulated over Nakagami- $m$ channels and verified through Monte Carlo simulations. The effects of HIs on the SEP of TAS-RISs-HIs communications are demonstrated through numerical illustrations. Specifically, the SEP of the TAS-RISs-HIs communications is significantly higher than the SEP of the ideal hardware communications with TAS and RISs, especially in the high transmit power regime. As a result, ignoring HIs when evaluating the SEP of the mmWave communications can result in some inappropriate conclusions. Moreover, the joint and separate advantages of TAS and RISs are thoroughly analyzed when comparing the SEPs in the cases with and without TAS, with and without RISs.