CeO2掺杂制备Ba0.9Ca0.1Ti1-xSnxO3压电陶瓷的结构及电性能

采用传统的陶瓷烧结技术,通过添加0.15%(摩尔分数)CeO2,在1120℃烧结2h,成功制备了新型无铅压电陶瓷Ba0.9 Ca0.1 Ti1-x Snx O3,并且检测了陶瓷样品的微结构和电性能.XRD显示所有陶瓷样品均具有纯的钙钛矿结构,在室温下为典型的四方相,SEM显示适量添加锡离子可以提高陶瓷致密性.在室温下,锡离子改性的BaTiO3基压电陶瓷在x=0.02处显示了优异的压电、介电和铁电性能(d33=276 pC/N,kp=46%,εr=3678,tanδ=2.4%,Pr=18.2μC/cm2,EC=1.12 kV/mm).这些优异的检测结果证实适当添加锡离子能改善BaT iO3基压电陶瓷的电性能.     

低温预氧化对PIP-SiCf/SiC复合材料介电性能的影响

分析了低温预氧化过程对聚碳硅烷(PCS)先驱体结构的影响,研究了不同预氧化温度和时间下SiCf/SiC复合材料室温和高温介电性能的演变规律。结果表明:经预氧化处理后基体中的氧含量增加,生成具有低介电常数的Si CxOy相,且其含量随着预氧化温度的升高或时间的延长逐渐增加,SiC微晶和自由碳的含量均减少,因此SiCf/SiC复合材料的复介电常数明显降低,同时高温复介电常数的升高幅度显著减小。经260℃-6 h预氧化处理后,700℃时复合材料在整个X波段的反射率均达到-8 d B以下,高温吸波性能得到有效改善。     

Optimization Techniques for Improving the Performance of Silicone‐Based Dielectric Elastomers

Dielectric elastomers are possible candidates for realizing products that are in high demand by society, such as soft robotics and prosthetics, tactile displays, and smart wearables. Diverse and advanced products based on dielectric elastomers are available; however, no elastomer has proven ideal for all types of products. Silicone elastomers, though, are the most promising type of elastomer when viewed from a reliability perspective, since in normal conditions they do not undergo any chemical degradation or mechanical ageing/relaxation. Within this review, different pathways for improving the electro‐mechanical performance of dielectric elastomers are highlighted. Various optimization methods for improved energy transduction are investigated and discussed, with special emphasis placed on the promise each method holds. The compositing and blending of elastomers are shown to be simple, versatile methods that can solve a number of optimization issues. More complicated methods, involving chemical modification of the silicone backbone as well as controlling the network structure for improved mechanical properties, are shown to solve yet more issues. From the analysis, it is obvious that there is not a single optimization technique that will lead to the universal optimization of dielectric elastomer films, though each method may lead to elastomers with certain features, and thus certain potentials.

     

Comparison of the RF MEMS switches with dielectric layers on the bridge’s lower surface and on the transmission line

Previously, we proposed that the dielectric layer of RF MEMS switch can be fabricated either on the transmission line, as traditional switches, or on the lower surface of the bridge. This paper presents a detailed comparison of the RF MEMS switches with different positions of dielectric layer. Through theoretically analyzing the physical model of fringing capacitance, it is revealed that different positions of dielectric layer can result in different switch capacitances. Therefore, the change of d...     

基于综合匹配的鸟类视频中运动物体的检测

鄱阳湖是中国最大的湿地。每年秋末冬初,会有成千上万只候鸟来此越冬,该地区的自然生态系统和这些鸟类的活动有着密切的联系,因此,研究该地区的鸟类是了解该地生态系统的一个重要方式。本文采用帧间差分法对该地所拍摄鸟类视频数据进行运动物体检测。由于视频在获取过程中存在摄像机的移动,所以在处理过程中首先需要估计背景的运动并加以补偿。背景运动的估计是在常用的块匹配方法的基础上作了一定的改进,通过多个匹配块的匹配结果来计算运动矢量。为提高正确率,块的匹配在差分图像上进行。最后,利用在鄱阳湖录取的视频对本文所述方法进行了实验,实验结果表明本文所述方法对背景的去除和运动物体的检测的有效性。     

基于帧间差分的足球球员检测算法

针对帧间差分法不能很好应用于变化场景的缺陷,提出了一种改进的帧间差分法,通过边缘提取、区域补偿等操作将该方法应用到足球视频中,对球员进行有效的检测.该方法首先利用颜色空间统计信息反投影技术得到运动场地,利用球场的主色对球场边缘进行补色,区域补偿,得到固定场景.利用帧间差分法检测球员,最后通过对球员候选区域的颜色信息与模板直方图匹配,达到对球员的队属辨别的目的.实验结果表明,该方法检测效果很好且具鲁棒性.     

Dielectric‐coated conducting curvilinear surface electrostatic model for spacecraft charging applications

In this article, free space capacitance of dielectric‐coated conducting curvilinear surfaces is obtained using method of moments (MOM). The surfaces are discretized using triangular subsections. The curvilinear surfaces are represented by quadratic parametric elements. The MOM based on the pulse basis function and point matching is used. The integrand is divided into a regular and a singular part. The regular part of the integral is numerically evaluated by using the Gaussian quadrature algorithm for triangles. The Duffy transformation is used to evaluate the singular part of the integrals. Computed results are given for the capacitance of the dielectric‐coated conducting cylinder of finite axial length and truncated cone, and compared with the previously published results. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Tri‐band composite cylindrical dielectric resonator antenna with hybrid mode excitation and cross‐polarization suppression

This communication investigates composite cylindrical dielectric resonator antenna (CDRA) for various wireless applications. Three important features of proposed antenna design are (i) realization of two different hybrid modes, that is, HEM_11δ and HEM_12δ mode in CDRA with the help of modified annular ring printed line (work as both magnetic dipole and electric dipole), both the hybrid modes support broadside radiation characteristics (ii) suppression of HEM_21δ mode, in order to reduce the cross‐polarization level in H‐plane of other hybrid modes (HEM_11δ and HEM_12δ mode) by an amount of 8‐10 dB (iii) creation of triple‐band attribute using the concept of composite antenna. The proposed antenna design has been fabricated and practically tested. Simulated outcomes show good agreement with measured outcomes. It works in three frequency bands, that is, 2.25‐2.79 GHz, 3.1‐4.0 GHz, and 5.05‐5.6 GHz. The designed antenna structure is appropriate for WLAN and WiMAX applications.     

基于传感技术的辛烷值测量

分析研究表明汽油的辛烷值与组成汽油的各个组份的综合介电常数ε有近似的对应关系。因此 ,利用电容式传感器测量ε的变化可以得出辛烷值。介绍了测量汽油辛烷值的传感器的原理及仪表。实验表明 ,与市售汽油辛烷值相比 ,测量精度可以达到± 0 .5个标号。