电阻层析成像系统全电极模型仿真研究

在电阻层析成像系统中,激励模式和电极数目的设计直接影响到整个系统。为了提高重建图像质量,更好地指导ERT系统设计,对敏感场进行深入的分析是必要的。通过电磁场有限元仿真软件COMSOL,构建ERT的电极模型,通过对空场和离散介质场域的仿真研究,分析了各个因素对敏感场的影响,并对四种典型流型进行了图像重建。仿真实验表明,COMSOL图像重建效果满意,为图像重建的研究提供了新的思路。     

高压脉冲电场处理室多物理场仿真研究

高压脉冲电场杀菌技术是一种新型的高效非热杀菌技术。高压脉冲电场处理室是杀菌处理的关键部件,其结构形式决定了处理室内部电场分布、温度场分布、流场分布,并影响杀菌处理的效果,同时电场强度和温度分布影响被处理食品的口味。以不同结构共场杀菌处理室为研究对象,利用COMSOL Multiphysics软件对共场杀菌处理室内部电场分布、温度场分布、流场分布对处理参数均匀性的影响进行了仿真。仿真结果表明,绝缘体无内嵌的处理室电场强度分布不均匀,对绝缘体倒椭圆角后的处理室可有效改善电场及流场分布,进而有效降低局部温升,改善处理效果。     

Design of Ag nanograting for broadband absorption enhancement in amorphous silicon thin film solar cells

Light trapping is one of the key issues to improve the light absorption and increase the efficiency of thin film solar cells. The effects of the triangular Ag nanograting on the absorption of amorphous silicon solar cells were investigated by a numerical simulation based on the finite element method. The light absorption under different angle and area of the grating has been calculated. Furthermore, the light absorption with different incident angle has been calculated. The optimization results show that the absorption of the solar cell with triangular Ag nanograting structure and anti-reflection film is enhanced up to 96% under AM1.5 illumination in the 300–800 nm wavelength range compared with the reference cell. The physical mechanisms of absorption enhancement in different wavelength range have been discussed. Furthermore, the solar cell with the Ag nanograting is much less sensitive to the angle of incident light. These results are promising for the design of amorphous silicon thin film solar cells with enhanced performance.     

A critical analysis of the performance of plate- and point-electrodes for determination of electrical properties of the soil mass

In the recent past, researchers have started utilizing electrical properties of the soil mass for its characterization by employing either plate- or point electrodes. Though, plate-electrodes are easy to use for laboratory experiments, and quantification of geometrical characteristics of the electric field generated within them is easy to quantify, their application for in-situ experiments and for samples of cylindrical shape becomes difficult. On the other hand, usage of point-electrodes which are cylindrical in shape, are used for moisture content determination of the soil or migration of contaminants in it, for coarse-grained soils and fine-grained soils might yield erroneous results, due to the presence of inter particle voids and presence of cavities & anomalies, respectively. Furthermore, quantification of geometrical parameters of the electric field of point-electrodes is quite difficult which results erroneous measurements in determination of electrical properties of the material, in which they are installed. Hence, establishment of the uniqueness of electrical properties obtained from the plate- and point-electrodes, for identical samples becomes utmost important. With this in view, COMSOL Multiphysics® was employed to simulate the electrical response of various geomaterials in their uncontaminated and contaminated states and results were critically evaluated vis-à-vis those obtained from the impedance analysis (1 Hz to 40 MHz). Efforts have also been made to relate the geometrical dimensions of electrodes and electric field generated across the point electrodes, which would facilitate proper design and installation of sensors in a material to achieve the desired output. This study demonstrates the suitability and versatility of the point-electrodes for various (field and laboratory) applications where in moisture profiling and contaminant transport is to be established.     

电极对薄膜体声波谐振器性能的影响

采用有限元分析软件COMSOL Multiphysics仿真了三维结构的谐振器,探讨了不同的顶电极形状对谐振器性能的影响。有效机电耦合系数(k2teff)随电极-压电层厚度比增大而减小,其中电极形状为三角形的谐振器在厚度比为0.05时获得最大k2teff(5.73%)。品质因数Q值变化趋势与k2teff相反,由三角形电极在厚度比为0.25时,获得最大Q值为1 314。不同电极形状的谐振器的优值随电极-压电厚度比先增大后减小,最大值为65.4,由正方形电极在比值为0.15时获得。     

ZnO单晶声表面波谐振器传播特性的研究

基于有限元压电材料中表面波传播的有限元分析原理,利用有限元分析软件COMSOL对基于ZnO单晶材料的声表面波器件进行多物理域耦合建模与仿真,提取出了符合声表面波振型的对称模态变形图和反对称模态变形图。通过谐振频率分析,计算出了ZnO单晶的相速度和机电耦合系数;通过频率响应分析,得出谐振器输入导纳、阻抗与频率之间的关系图;最后讨论了叉指换能器的结构对谐振频率、反谐振频率的影响,得出输入、输出叉指换能器(IDT)的叉指电极对数越大,插入损耗值越大,信号衰减越小。     

软脆铌酸锂晶体磨削的实验仿真研究

针对铌酸锂晶片在磨削加工时经常发生断裂的问题,对晶片断裂的原因进行了理论分析,并从晶体学的角度分析发现断裂与实验采用的晶片晶体结构有关。提出了基于多物理场耦合软件COMSOL Multiphysics对铌酸锂晶片磨削加工仿真的方法,为模拟铌酸锂晶片磨削减薄过程,对比分析了7种不同厚度的铌酸锂晶片在磨削加工时的应力分布和变形情况,对有外加电载荷磨削加工情况也进行了耦合仿真。研究结果表明,未施加电场时铌酸锂晶片的变形量随着晶片减薄过程逐渐减小,当铌酸锂晶片减薄至80μm时,晶片的外围出现均匀分布的4个应力集中位置,容易导致晶片产生裂纹甚至破裂;铌酸锂晶片变形量因外加电载荷而减小,因此合理施加外电场能够有效减弱晶片的应力集中趋势。     

基于COMSOL Multiphysic的煤层甲烷拟稳态吸附-运移数值模拟

由于煤层甲烷在煤岩体中的运移过程及其复杂，因此用来描述其运移的数学模型常常是高阶非线性的偏微分方程，为了能更好的解决此类问题，本文采用多重物理量数值模拟软件COMSOLMultiphysic对所建的拟稳态运移模型进行了模拟求解的研究，结果表明用该软件模拟的压力和浓度动态曲线更符合实际情况，而且可以用动态可视化模块来模拟压降过程。     

一种复合式MEMS皮拉尼真空计的设计

微电子机械系统(MEMS)皮拉尼真空计可广泛用于芯片封装和设备测试等领域.量程是MEMS皮拉尼真空计的重要性能指标之一.设计了一种复合式MEMS皮拉尼真空计,通过将具有不同测量范围的两款器件串联复合在同一芯片上,实现量程的扩展.以二极管型皮拉尼真空计为例设计了器件结构,优化了尺寸参数,并给出了兼容CMOS工艺的制造方案...