Piezoelectromagnetic waves guided by the surface of a ceramic cylinder

Summary The propagation of shear horizontal (SH) waves over the surface of a circular cylinder of polarized ceramics is studied from the three-dimensional equations of linear piezoelectromagnetism with full electromagnetic coupling. An exact solution is obtained.     

Sol–gel alumina environmental barrier coatings for SiC grit

SiO₂ surface film is insufficient to protect SiC from the oxidation at widely varying partial pressures of oxygen, in particular in the presence of water vapor (e.g. in gas turbines) and also in other environments, e.g. during brazing for hard “tipping” of turbine blades. This work demonstrates that sol–gel alumina, coated on 0.5 mm coarse SiC grit, may form an acceptable, up to 10 μm thick “environmental barrier coating” EBC for some of these applications. The sol–gel has advantages over other methods (such as CVD) is the simplicity and low cost. We have used NH₄OH pre-treatment to hydroxylate surface of SiC prior to applying alumina coating. Such modified SiC/SiO₂ surface helped to deposit the positively charged alumina sol, and thus allowed to build thick coatings on the SiC grit. There is some indication that these coatings partially convert to mullite through reaction at the interface with the native silica on SiC. Oxidation resistance tests at 1200 °C were performed to show effectiveness of such coated SiC grit.     

Fabrication and characterization of Zr and Co co-doped LiMn2O4 nanowires using sol–gel–AAO template process

The Zr and Co co-doped LiMn₂O₄ nanowires are fabricated successfully by using sol–gel process with porous anodic aluminum oxide (AAO) as the template. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization show that the synthesized LiZr _x Co _y Mn_(2-x-y)O₄ nanowires are uniformly distributed, high-ordered, and parallel to each other, and few microscopic defects are found. Selected area electron diffraction (SAED) pattern, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) investigations jointly demonstrate that the synthesized nanowires have a similar single spinel structure of LiMn₂O₄ crystal though Zr and Co are doped. Since the LiZr _x Co _y Mn_(2-x-y)O₄ nanowires can be mass-produced by using this method, it is expected to find promising application as a new cathode material in lithium ion battery.     

Structural reliability assessment of multi-stack package (MSP) under high temperature storage (HTS) testing condition

Wire ball open failure at the interface of the gold wire and bonding pad of a multi-stack package (MSP) under high temperature storage (HTS) condition of 150 °C is studied. Failure analysis using FIB-SEM was conducted by in-plane moiré interferometry and FEA to clarify the failure mechanism. The ball open failure due to Kirkendall void that results from metal diffusion at high temperature was accelerated by the tensile stress imposed at the gold wire. The tensile stress developed at the gold wire when packages showing different warpage behaviours were stacked. Mechanical interaction between top and bottom packages caused unstable warpage, readily twisted and saddled. The wire came in contact with the photo-sensitive solder resist (PSR) dam because of the unstable warpage and this contact resulted in tensile stress at the gold wires. Solder flux residues reacted with the encapsulant, and as a result, the encapsulant of the top package adhered to the chip of the bottom package, and this adherence created additional tensile stress at the gold wires. To reduce the tensile stress at the wires, the PSR dam was removed, loop shape was altered from 45° to 90°, water soluble flux was applied, and cleaning process was added. HTS reliability was significantly improved and guaranteed after reducing the tensile stress at the wires.     

基于MATLAB的控制器设计研究

文章首先对MATLAB软件作了简要的介绍,强调了它目前在各个领域中都得到了广泛的应用。接着总结了控制系统校正的主要方法,包括串联校正和反馈校正等。最后结合两个具体的例子,给出了利用MATLAB设计出不同的控制器的方法。     

基于DDS的快速跳频源设计

在简要介绍跳频通信技术的发展概况及跳频源合成主要方法的基础上,针对目前普遍采用的DDS技术,详细分析了其输出频谱特性,并由此引出了基于DDS的跳频源设计方案,然后详细分析了设计原理、实现的可行性以及软件的设计和流程图,同时对主要芯片的性能指标及特点作了说明。此设计通过优化,提高了各项性能指标,对整体跳频通信收发机的性能有了很大的提升。     

三相异步电动机控制网络虚拟实验系统的设计实现

本文介绍了基于Internet的三相异步电动机虚拟实验制作思路,重点阐述了设计制作实验时模型的定义、界面设计和实验程序设计,为相关实验设计提供了一种思路。     

配合煤选择性粉碎工艺的应用

介绍了配和煤选择性粉碎工艺的原理、特点及应用情况。结果表明该工艺投用后，配合煤质量明显改善。     

生成黑盒测试数据的设计思想在学生成绩管理系统中的实现

黑金测试是数据库应用系统测试的常用方法，而生成大量测试数据则是进行黑金测试的前提。如果能使用“数据生成”工具生成大量模拟测试数据，将提高数据库应用系统的测试效率和测试质量。本文主要提出了生成黑金测试数据的设计思想，并基于这一思想开发了“学生成绩管理系统”的数据生成工具。