逆向工程中自由曲面的自适应数字化算法研究

分析比较了对自由曲面自适应测量的几种方法。在有界曲率的平面曲线的有界性的基础上，提出圆弧外延法，即后续测量点根据已测前三点求得的圆弧曲率沿切线方向或等曲率外延来进行预测，并根据测点矢量来估测保证数字化几何信息的充分性。这样就可利用待测曲面的几何(曲率)特性，使得测点的分布与曲面的曲率保持一致。最后给出了对这一算法的仿真结果。     

曲面形貌轮廓仪传感器的机构设计

介绍一种适于曲面形貌测量的新型触针式轮廓仪的传感机构。它采用顶尖支承作为测杆的支承形式，并以测杆自重为传感器的测力源，无导头。本文分析了其动态特性和动态测力问题。     

基于共面波导传输线的宽频带介电常数提取方法

提出了一种基于共面波导传输线的宽频带低损耗材料介电常数提取方法。设计5根共面波导传输线作为标准覆盖待测样品介电常数频率范围,采用在片矢量网络分析仪测得各传输线未经修正的S参数,经过多线TRL校准算法提取传播常数;采用quasi-TEM模型计算传输线的单位长度电阻R和单位长度电感L;最终求得0.1~50GHz GaAs材料的介电常数。相比于传统的腔体法只能点频测试,且需设计待测样品腔体结构,该测试方法支持宽频带介电常数的连续测试,且测试效率更高;测试结果与谐振腔法偏差±2.5%,满足工程实践需要。     

基于Helmholtz方程的过渡曲面设计

阐述了二阶和四阶Helmholtz方程的一类周期边界问题的差分解法及其在过渡曲面设计中的应用。这类方法不同于传统的PDE方法中的二阶和四阶的偏微分方程,比传统的二阶和四阶偏微分方程有了更多的自由项,因此,在曲面设计的时候,就有更多的形状控制参数可进行调整,文中重点讨论了方程中的系数对曲面形状的影响,并研究了边界切矢条件对曲面形状的影响及其在曲面形状设计中的应用。设计者只需给出边界曲线和边界切矢,并通过对它们的控制就可构造和修改曲面形状。     

一种抗杂波无芯片RFID介电常数传感器标签的设计

针对感知自然环境中材料介电常数的应用,本文提出一种具有较好抗环境杂波的无芯片射频识别(RFID)传感器标签的设计.标签谐振器结构具有极化变换特性并含金属接地板,接收机采用正交方式收发信号,可将环境产生的干扰杂波有效滤除.标签编码由4组不对称Z型金属条带谐振器实现,结构紧凑且相互耦合小.传感谐振器的金属贴片具有阶梯型缝隙...     

基于半球形测头的自由曲面截形测量方法

提出的半球形测头测量自由曲面任意截形方法避开了用球形测头测量曲面的复杂过程和由此产生的三维测头半径补偿的数学模型及大量运算，消除了在三维曲面截形测量时由于被测曲面的扭曲对测头所造成的干涉，可使曲面测量直接转化为曲线测量，从而大大简化了测量和数据处理过程。     

基于MKSA算法的曲面自适应采样

针对在机测量传统采样方法存在的采样点过于集中和采样区域遗漏影响曲面轮廓度的问题,将MacQueen K-means(MK)算法与模拟退火(SA)算法相结合,提出基于MKSA的复杂曲面在机测量自适应采样方法。利用MK算法生成二维质心Voronoi结构(CVT结构),将复杂曲面离散点云数据的高斯曲率绝对值作为生成CVT结构的密度函数,以方差函数为收敛准则,通过全局算法SA的退火准则设置降温系数,提高MK算法的全局寻优能力,生成全局最优的二维CVT结构;将质心点映射回原曲面,获得质心位置对应的曲面采样点,从而实现复杂曲面的自适应采样。仿真及实验结果表明:MKSA算法使曲面测量采样点分布更合理,拟合曲面与CAD模型的最大偏差及平均偏差均小于传统方法,更逼近CAD模型的理论曲面。     

基于扭曲面的螺旋桨桨叶曲面设计研究

为实现螺旋桨桨叶外形设计和制造的自动化,利用了扭转曲面的概念。在对桨叶曲线、曲面数学描述的基础上,建立了直纹曲面的矢量方程,推导出螺旋桨桨叶扭转曲面精确的数学方程。并构造出扭转曲面与圆柱面光滑连接的曲面方程,顺利实现了两种曲面的光滑连接。为计算机辅助设计和制造类似这种扭转曲面,提出了一种新的解决方法。     

基于纳米多孔性聚合物低介电常数材料的研究进展

综述了纳米多孔性聚合物基低介电常数材料研究工作的基本情况。着重介绍了以聚酰亚胺、聚硅氧烷和环氧树脂为基体的纳米多孔低介电常数材料的研究进展,并对研究前景做了展望。     

基于ANSYS的铝蜂窝夹芯板低速冲击仿真模拟研究

简要介绍了蜂窝夹芯板的结构及特点,利用ANSYS有限元模拟软件模拟分析了小球低速冲击对蜂窝铝板的损伤变形,在冲击条件参数不变的情况下,研究了蜂窝铝板结构参数(蜂窝芯边长、蜂窝芯壁厚、蒙皮板厚)对冲击变形以及吸收能量的影响。结果表明,冲击速度越快,能量吸收系数越高,蜂窝芯厚度、蒙皮板厚度增加和蜂窝芯边长减小均使蜂窝铝板耐冲击能力有所提升。     

Application of the dielectric constant measurements to study the influence of the small quantities of water vapor on the compressibility factor of methane

Dielectric measurements have been applied successfully to obtain accurate values of the compressibility factor of methane in the presence of the small quantities of water vapor [20, 65, and 95 ppm(v)]. Up to about 95 ppm(v) of H₂O in CH₄, the compressibility factor decreases very slightly in the presence of H₂O. The compressibility factor of dry CH₄ determined by the dielectric method is compared with the best PVT results and the Goodwin equation of state. The compressibility factor of CH₄ having small quantities of water vapor is compared with the Goodwin, GERG, and AGA8 equations.     

Effect of etching on dielectric constant and surface composition of SiCOH low-k films in inductively coupled fluorocarbon plasmas

SiCOH low-k (k = 2.8) film etched in fluorocarbon (CF₄ and CHF₃) inductively coupled plasmas was characterized in this work. The surface composition and molecular structures of the low-k films after etching in the CF₄, CHF₃, CF₄/Ar, and CHF₃/Ar plasmas were characterized. A higher etch rate was observed with the CF₄ plasmas than with the CHF₃ plasmas. The etch rate of the low-k film in the CF₄ plasmas was decreased and the etch rate in the CHF₃ plasmas was increased by the Ar addition. After etching the low-k films, a decrease in the dielectric constant of up to 0.19 was observed. The thickness of the fluorocarbon (CF_x) layer and CF_x (x = 1, 2, 3)-to-carbon ratio obtained from the XPS C 1s peak increased with decreasing etch rate. The k-value was correlated with amount of Si-CH₃ and Si-O related groups determined from the Fourier transform infrared (FT-IR) spectrum. The Si-O related peaks were markedly decreased after etching in the CF₄ and CF₄/Ar plasmas. The lower k-value was attributed to the increase of the Si-CH₃/Si-O ratio after etching low-k film.     

基于屈服面的曲线梁桥地震动最不利输入方向

曲线梁桥由于线形、刚度及质量的不规则分布,需要研究其地震动最不利输入方向。Bresler屈服面给出了钢筋混凝土构件在轴压力与双向弯矩组合作用下的截面屈服条件,本文据此将地震中桥墩截面最易发生屈服的方向定义为最不利地震动输入方向。在应用反应谱法得到两个正交方向地震反应的基础上,提出了基于Bresler屈服面的地震动最不利输入方向的一种新算法,该法考虑了水平面内双向地震动共同作用及曲线梁桥振型间的相关性。进一步,给出基于时程分析法的地震动最不利输入方向确定算法。最后,以某闭合圆环匝道桥为对象,分析了各墩的地震动最不利输入方向,同时验证了方法的准确性。     

高介电常数BaTiO3陶瓷畴反转电流影响因素的研究

采用溶胶-凝胶结合二次煅烧的方法制备了高介电常数BaTiO3陶瓷,通过X射线衍射分析得到所制备的体系为四方相和立方相共存结构,从扫描电镜的图像中能观察其晶粒尺寸为1μm。通过TF2000铁电分析仪得到其介电常数在煅烧温度为1310℃,保温时间为4h,室温、测试频率为100Hz、测试电压为100V的条件下最大值为38306。研究了BaTiO3铁电陶瓷的反转电流随温度、频率和电压的影响规律,研究发现随着温度的升高反转电流缓慢降低,而随着电场和频率的增加反转电流迅速升高。从能量的观点也能进一步分析温度和电场对于反转电流的影响。     

滤波求和恒定束宽波束形成器设计

文章在深入分析连续阵的恒定束宽波束形成理论基础上，将阵元权系数等效为两级滤波器，第一级只该与基阵的孔径分布有关，第二级只与基阵的维数有关，给出了滤波器的设计方法。通过时域的滤波求和实现恒定束宽波束形成，避免了频域分解，降低了运算量。该方法可用于一维、二维和三维情况，并且适用于任意带宽。基于非均匀线阵的计算机仿真表明该方法的恒定束宽效果是令人满意的。     

紫外辐照对超低介电常数SiCOH薄膜组成与机械性能的影响

采用紫外光辐照超低介电常数多孔SiCOH薄膜,研究不同照射时间对薄膜结构和性能的影响。采用动态纳米压入技术测量薄膜的力学性能,发现随照射时间增加,薄膜的模量（Er）和硬度（H）不断提高。当辐照时间增至6h时,薄膜力学强度分别达到Er约7.4GPa,H约1.0GPa。傅里叶变换红外光谱（FT-IR）、X射线光电子能谱（XPS）分析表明紫外辐照处理能够使薄膜样品中发生键的断裂与重新结合,从而改变了薄膜骨架的交联密度和刚性,进而提高力学性能。但介电性能并未受到明显影响,紫外辐照6h后,k值仅从2.0增至2.2。     

Influence of relative humidity on the nanoscopic topography and dielectric constant of thin films of PPy:PSS

The morphological, electric, and dielectric properties of water-based conjugated polymer blends, such as polypyrrole:polystyrene sulfonate (PPy:PSS) or poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), are known to be influenced by the water content. These properties also influence the macroscopic performance when the conjugated polymer blends are employed in a device. An in situ humidity-dependence study on thin films of PPy:PSS by Kelvin probe force microscopy (KPFM) is presented. A particular KPFM mode, dielectric imaging, is used, which detects the second harmonic electrostatic force. Thin PPy:PSS films are drop-coated on hydrophobic graphite substrates. Upon increasing the relative humidity, the hydrophilic PSS is swelled and dewetted on the substrate, while the hydrophobic PPy remains almost unchanged. The swelling and dewetting of PSS results in irreversible morphological changes in the thin films, as well as nanoscopic rearrangement on the surface of the PPy:PSS films. The nanoscopic rearrangement can only be detected by dielectric imaging. It is also observed that relative humidity affects unannealed and thermally annealed PPy:PSS thin films differently.     

Electrophysical method for evaluating the fracture surface energy of dielectric materials in contact with metal

A physical model is formulated and the method is substantiated for measuring the fracture surface energy of dieletric materials. An analogy between the distributions of electric field intensity and mechanical stresses close to the metal-dieletric surface contact is used.Translated from Izmeritelnaya Tekhnika, No. 10, pp. 52–56, October, 2004.     

基于介电弹性体的振荡水柱波浪能发电模拟分析

振荡水柱式(OWC)波浪能采集装置结构简单、成本低;介电弹性体作为发电机可以收集人体能、海洋能、风能等,能量密度高、耐冲击、环境适应性强,利用OWC驱动介电弹性体形变发电应用前景好。在FLUENT中建立二维数值水槽OWC模型分析气室内波高和压强的变化规律;在Abaqus有限元分析系统中将波浪进入气室的模拟压强施加到介电弹性体薄膜模型产生形变,采用Simulink计算介电弹性体发电量。结果表明:介电弹性体发电量随着薄膜面积、气室压强增加而增大;随着薄膜厚度、预拉伸强度增大而减小,并且这两者对发电量影响较大。     

Differential laser trigonometry for measuring the oil film thickness on water

A differential laser trigonometry method is presented for measurement of the oil film thickness on a water surface. The thickness of an oil film can be obtained with two off-plane displacements to a benchmark plane obtained by the imaging spot displacement and the configuration parameter of the imaging system subtracted. The method has been tested in the laboratory via the examination of diesel oil and petroleum films. An experimental system setup has been developed, by which the maximum measurable thickness is 12?mm and the average measurement error is 6.05?µm. The results show that the method presented is feasible, and applicable to dynamic online measurement of oil film thickness of oil spills on the sea surface.