压电加速度传感器有限元仿真方法研究

压电加速度传感器具有频带宽,结构简单,耐高温性能好等特点,在复杂机械应力和高温应力环境下应用广泛,是航空发动机健康监测、爆炸冲击监测等应用下必不可缺的器件。对于压电加速度传感器的设计和研究,常使用有限元仿真法来分析其固有频率、响应及在此基础上的各种机械应力、温度应力下的状态。从压电加速度传感器的原理、结构和有限元仿真的基本流程出发,调研了压电加速度传感器有限元仿真中的主要问题。按照不同结构类型总结了建立几何模型时的结构简化方法,分析了螺栓预紧力的主要仿真方法;区分部分仿真和整体仿真,总结了固有频率的仿真方法;按照不同激励,讨论了不同应力的仿真实现方法。     

巡飞攻击导弹红外成像导引头瞬态冲击响应分析

以巡飞攻击导弹红外成像导引头为研究对象,从理论上对系统的半正弦波冲击响应进行了分析,给出了响应计算方法。建立了导引头有限元分析模型,利用ANSYS Workbench有限元分析软件,对导弹在发射及飞行过程中导引头需承受的发射冲击和分离冲击进行了分析计算,分析了导引头的应力、应变及探测器的加速度响应,计算结果表明导引头能承受住发射及分离过程的冲击激励作用。     

Cryptanalysis and improvement of ‘a robust smart‐card‐based remote user password authentication scheme’

With the use of smart card in user authentication mechanisms, the concept of two‐factor authentication came into existence. This was a forward move towards more secure and reliable user authentication systems. It elevated the security level by requiring a user to possess something in addition to know something. In 2010, Sood et al. and Song independently examined a smart‐card‐based authentication scheme proposed by Xu et al. They showed that in the scheme of Xu et al., an internal user of the system can turn hostile to impersonate other users of the system. Both of them also proposed schemes to improve the scheme of Xu et al. Recently, Chen et al. identified some security problems in the improved schemes proposed by Sood et al. and Song. To fix these problems, Chen et al. presented another scheme, which they claimed to provide mutual authentication and withstand lost smart card attack. Undoubtedly, in their scheme, a user can also verify the legitimacy of server, but we find that the scheme fails to resist impersonation attacks and privileged insider attack. We also show that the scheme does not provide important features such as user anonymity, confidentiality to air messages, and revocation of lost/stolen smart card. Besides, the scheme defies the very purpose of two‐factor security. Furthermore, an attacker can guess a user's password from his or her lost/stolen smart card. To meet these challenges, we propose a user authentication method with user anonymity. We show through analysis and comparison that the proposed scheme exhibits enhanced efficiency in contrast to related schemes, including the scheme of Chen et al. Copyright © 2013 John Wiley & Sons, Ltd.     

MEMS Inductor Consisting of Suspended Thick Crystalline Silicon Spiral with Copper Surface Coating

报道了一种由悬浮在玻璃衬底上的表面镀铜平面单晶硅螺线构成的新型MEMS电感,可消除衬底损耗及减小电阻损耗.采用一种硅玻璃键合-深刻蚀成型释放工艺并结合无电镀技术制作该电感,形成厚约40μm的硅螺线,在硅螺线表面镀有高保形厚铜镀层,在铜镀层表面镀有起钝化保护作用的薄镍镀层.该电感的自谐振频率超过15GHz,在11.3GHz下,品质因子达到约40,电感值超过5nH.基于该电感的简化等效电路模型,采用一种特征函数法进行了参数提取,模拟结果与测量结果符合得很好.     

用于喇曼放大的SOI脊形波导中自由载流子寿命的解析表达

研究了用于喇曼放大的绝缘硅(SOI)脊形波导中自由载流子寿命与非线性光学损耗的关系.通过理论推导结合二维数值模拟的方法,提出了带有零反偏pin结构的SOI脊形波导中自由载流子寿命的解析表达式,该解析表达式与他人的实验结果相符.结果表明,比起不带pin结构的波导,带有零反偏pin结构的波导中的自由载流子寿命最多可以缩短80%.同时,研究了pin结构外加反偏电压时,自由载流子寿命进一步缩短的原因,并从强场下自由载流子速度饱和的角度出发,得到了自由载流子寿命的理论极限值.最后,模拟了不同自由载流子寿命情况下SOI脊形波导的喇曼净增益随着输入泵浦光功率密度的变化曲线,为硅基喇曼放大器的进一步研究指明了方向.     

一种基于TDA16846的新型有源功率校正电路设计

介绍一种由集成电路芯片TDA16846完成的利用电荷泵(Charge Pump)实现的有源功率因数校正(APFC)技术。这种APFC电路的突出优点就是结构简单,通过对常规缓冲电路进行合理调整,可以很容易变成具有PFC功能的高性能开关电源。分析了APFC的工作原理,应用专用芯片TDA16846设计了电路图,并阐述了主要元件的功能。经实验证明,推荐电路设计合理,应用前景广阔。     

槽式聚光太阳能系统太阳电池阵列

基于槽式聚光太阳能系统分别对单晶硅电池阵列、多品硅电池阵列、空间太阳电池阵列和砷化镓电池阵列进行测试实验.结果表明,聚光后,前3种电池阵列的Ⅰ-Ⅴ曲线都趋于直线,输出功率急剧减少,系统效率下降较快.而砷化镓电池阵列有较好的Ⅰ-Ⅴ曲线,其效率由聚光前的23.66%增加到26.50%,理论聚光比为16.92时,输出功率放大11.2倍,聚光光伏系统中町采用砷化镓电池阵列以提高效率.砷化镓电池阵列Pm、FF和η的温度系数分别为-0.12W/K、-0.10%/K和-0.21%/K,为避免温度的影响须采用强制冷却方式保证电池效率,同时对外供热.研究表明,10片单晶硅电池串联阵列最佳工作时的理论聚光比为4.23;16片空间太阳电池串联阵列最佳工作时的理论聚光比为8.46.研究工作对提高槽式聚光系统效率和大规模利用聚光光伏发电提供了依据.     

电阻加载在宽带均衡器中的应用

给出了1种宽带的功率均衡器的快速设计方法。分析了均衡网络中加载电阻后谐振单元的谐振和耦合特性,并讨论了加载电阻对谐振单元品质因数的影响。对谐振单元的尺寸和电阻进行设定和调整,并使用仿真软件对级联网络进行优化,可以在短时间内设计出满足目标的均衡器。基于本方法,设计了2种频段的宽带功率均衡器。     

Neuro-Glia-Vascular-on-a-Chip System to Assess Aggravated Neurodegeneration via Brain Endothelial Cells upon Exposure to Diesel Exhaust Particles

Air pollution induces neurodegeneration, including cognitive deficits, neuroinflammation, and disruption of the blood–brain barrier. The mechanisms underlying air pollution-mediated neurodegeneration have not yet been fully elucidated given the limited knowledge on intercellular interactions. A brain-on-a-chip platform is presented comprising neurons, glia, and brain endothelial cells (bECs; neuro-glia-vascular, NGV) and diesel exhaust particle (DEP)-induced neurodegeneration is evaluated with a particular focus on the intercellular interactions. DEP exposure in the NGV model yields Alzheimer's disease-like signatures, including amyloid beta accumulation, tau phosphorylation, hydrogen peroxide (H₂O₂)/reactive oxygen species (ROS) production, and neuronal cell death. bEC-secreted granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates microglial activation and the overproduction of H₂O₂/ROS in microglia, suggesting that the bEC-microglia-neuron is a neurodegeneration cascade. Pharmacological inhibition at each step of the cascade, including GM-CSF neutralization, microglial activation suppression, and ROS scavenging, prohibits neurodegeneration in the NGV model. Therefore, intercellular interactions should be further studied of air pollution-induced neurodegeneration.     

Interfacial Connections between Organic Perovskite/n+ Silicon/Catalyst that Allow Integration of Solar Cell and Catalyst for Hydrogen Evolution from Water

The rapidly increasing solar conversion efficiency (PCE) of hybrid organic–inorganic perovskite (HOIP) thin-film semiconductors has triggered interest in their use for direct solar-driven water splitting to produce hydrogen. However, application of these low-cost, electronic-structure-tunable HOIP tandem photoabsorbers has been hindered by the instability of the photovoltaic-catalyst-electrolyte (PV+E) interfaces. Here, photolytic water splitting is demonstrated using an integrated configuration consisting of an HOIP/n⁺silicon single junction photoabsorber and a platinum (Pt) thin film catalyst. An extended electrochemical (EC) lifetime in alkaline media is achieved using titanium nitride on both sides of the Si support to eliminate formation of insulating silicon oxide, and as an effective diffusion barrier to allow high-temperature annealing of the catalyst/TiO₂-protected-n⁺silicon interface necessary to retard electrolytic corrosion. Halide composition is examined in the (FA_1-xCs_x)PbI₃ system with a bandgap suitable for tandem operation. A fill factor of 72.5% is achieved using a Spiro-OMeTAD-hole-transport-layer (HTL)-based HOIP/n⁺Si solar cell, and a high photocurrent density of −15.9 mA cm⁻² (at 0 V vs reversible hydrogen electrode) is attained for the HOIP/n⁺Si/Pt photocathode in 1 m NaOH under simulated 1-sun illumination. While this thin-film design creates stable interfaces, the intrinsic photo- and electro-degradation of the HOIP photoabsorber remains the main obstacle for future HOIP/Si tandem PEC devices.