折板基础的有限元分析及简化计算

将作用于折板上的地反力换算成等效的均布荷载,根据构造措施和实际受力情况,可按周边固定的单元板进行计算,对折板基础进行有限元分析,并与弯矩分配法计算结果进行比较,说明有限元方法与弯矩分配法的计算结果基本吻合,同时能提供更详尽的数据,是分析折板基础的可靠方法。     

折板网壳的几何非线性分析

折板网壳是一种新型的网格形式。在介绍几种适用于矩形平面形状的折板网壳基础上 ,进一步将这种结构与平板网架在强度、刚度、稳定性和经济性方面作了比较分析。结果表明 ,该种结构具有良好的受力性能。此外 ,还分析了这种结构的几何非线性性能     

Miniaturized piezoelectric energy harvester for battery‐free portable electronics

This paper describes a miniaturized energy harvester based on the interaction of two permanent magnets placed on both ends of a folded cantilever made with piezoelectric thin films. A unique design of the folded cantilever structures is developed to efficiently collect ambient vibrational energy over a wide frequency bandwidth for the operation of battery‐free electronic devices. The output performance of the two energy harvesters is observed to improve significantly through the use of the mutual coupling technique. The folded cantilever structure also demonstrates improved space efficiency compared with the conventional rectangular cantilever design. A wide frequency band and sufficient energy‐harvesting ability were successfully achieved by the optimally manufactured device. The maximum output power of the miniaturized energy harvester was 41.6 μW with an impedance of 0.3 MΩ. Furthermore, a pedometer was powered completely by the energy harvester without the need for any battery and external power source, demonstrating the potential of the proposed design for self‐powered electronics applications in a vibrational environment.     

Theoretical and numerical analysis of the folding mechanism of vertex-based hierarchical honeycomb structure

Abstract

This study presents numerical and theoretical investigation for the vertex-based hierarchical honeycomb structure subjected to axial compression. Mechanical behavior as well as predictable formulas were explored based on folded element and Minimal Energy Principle. Parametric studies were numerically conducted with different scale ratio, and the influence of wall thickness on mechanical performance was determined. Good agreement was observed between the numerical results and theoretical solutions, which validates the analytical model well. Furthermore, deformation mode comparisons were conducted between vertex-based hierarchical honeycomb and other filled-type honeycomb structures. Evident promotion on energy absorption was obtained for vertex-based hierarchical honeycomb.     

Study on morphology and crystal growth of syndiotactic polystyrene solution-grown crystals by transmission electron and atomic force microscopy

The morphology of solution-grown crystals (SGCs) of syndiotactic polysthyrene (s-PS) has been investigated using transmission electron and atomic force microscopy (TEM and AFM). Well-defined s-PS SGCs were prepared from 0.005% (w/w) n-tetradecane/decahydronaphthalene solution 2:1 (v/v) by an isothermal crystallization method at 200 °C. Lattice constants for this crystal estimated by TEM with the diffraction mode are a=0.90 nm, b=2.88 nm. AFM images of the folded chains on the surface of s-PS SGC suggested their alignment parallel to the direction of the growth face of the truncated-lozenge shaped crystal. The angle between the growth faces obtained from s-PS SGCs was 130°. Since, the value of 130° correspond to the {230} angle, the primary growth face of s-PS SGC was assigned to the (230) plane.     

内嵌于多层封装基板的折叠波导慢波结构设计

提出了一种新型的内嵌于多层封装基板的折叠波导慢波结构。开展了此慢波结构的解析模型、色散特性和耦合阻抗、射频传输特性以及注—波互作用的研究。通过理论分析、数值计算和仿真优化得到了较好的结果。在W波段该结构呈现反射小、损耗低,易于加工等特点。在中心频率94 GHz处色散曲线较为平坦,耦合阻抗值在2Ω左右。同时,对低温共烧陶瓷的材料特性及加工工艺进行了研究,探讨了该结构实现加工的可行性。     

W波段低电压宽带过模矩形同轴曲折波导行波管的研究

提出了一种具有高频率、宽频带和低电压特点的矩形同轴曲折波导慢波结构,所提出的矩形同轴曲折波导工作于过模状态,工作频率较高,同时具有不错的传输特性。设计了一种宽带的双脊加载的波导-同轴转换器,其带宽可以覆盖矩形同轴曲折波导行波管的整个工作频带。所设计的矩形同轴曲折波导行波管工作电压和电流分别为3230 V和150 mA,慢波结构长度为32 mm,PIC仿真结果表明,在76～110 GHz频率范围内,其输出功率超过13.7 W,在108GHz频点,输出功率达到最大值,约为27.4 W,对应的射频效率为 5.65%。     

Turbo译码中的Log-MAP折线逼近法

为了在降低Turbo系统译码延时的同时仍保证其优良的低误比特率性能,本文提出折线逼近法方案。该方案只用比较器和加减法,就能在保证Turbo码低误比特率的前提下,有效降低系统延时和译码复杂度。仿真结果表明:折线逼近法的译码性能大大优于Max-Log-MAP方法,同时比二次幂逼近算法降低1.5倍以上的系统延时。     

一种新型两通道时间交织高阶∑△调制器

为了减小两通道时间交织∑△调制器中系数失配引起的折叠噪声以及降低调制器实现电路的复杂程度,提出了一种新的两通道时间交织高阶∑△调制器.在传统调制器的噪声传递函数(NTF)中增加一个z为-1的零点,减小了NTF在高频处的幅值,从而减小了折叠到信号带宽内的噪声.以一个传统单通道单环4阶4位前馈分布型∑△调制器结构为原型,运用块数字滤波器基本原理以及时域等效的方法,得到了其两通道时间交织结构的实现电路.该调制嚣电路前3级的两个通道能够共享运算放大器,减小了有源元器件的数目.对包含了系数失配的调制器进行了建模和仿真,仿真结果表明,该两通道时间交织高阶调制器能够有效地抑制折叠噪声,提高了调制器的性能.