Design of diamond-shaped transient thermal cloaks with homogeneous isotropic materials

Transformation thermodynamics as a major extension of transformation optics has recently received considerable attention. In this paper, we present two-dimensional (2D) and three-dimensional (3D) diamond-shaped transient thermal cloaks with non-singular homogeneous material parameters. The absence of singularity in the parameters results from the fact that the linear coordinate transformation is performed by expanding a line segment rather than a point into a region, while the mechanism behind the homogeneity is the homogeneous stretching and compression along orthogonal directions during the transformation. Although the derived parameters remain anisotropic, we further show that this can be circumvented by considering a layered structure composed of only four types of isotropic materials based on the effective medium theory. Numerical simulation results confirm the good performance of the proposed cloaks.     

基于最优延时和多天线的并行检测算法

循环平稳特征检测是一种在低信噪比时也能准确发现信号的盲检测技术,但其算法计算周期较长.针对此问题提出了一种改进的并行渐进最优卡方检测算法,通过识别循环谱特性和遍历循环自相关确定最优的循环频率和延时,用循环自相关以及渐进协方差矩阵构建检验统计量,并对二维向量和谱分量实部和虚部进行合并及迭代过程并行处理,仿真得到了检测概率和检测时间.同时,根据最大似然比统计量的有偏估计和渐进分布特性导出了检测概率的表达式,结果表明:最优延时的理论与仿真吻合得很好,多天线技术充分利用了空间分集,在干扰较强时仍然具有较高的检测概率,且并行处理过程能有效减少检测时间.     

Orbital Angular Momentum Generation Using Circular Ring Resonators in Radio Frequency

Electromagnetic field generators based on circular ring resonators,whose perimeters are integer times of equivalent wavelength,are well known to have attractive potential for producing radio vortexes carrying orbital angular momentum(OAM).We study the radiation characteristics of the generators based on radiation vector and antenna array theory.The behaviors of radiation patterns,field intensity and phase distribution are investigated in detail,and show classical features of OAM beams.The evolution of the generators performance versus the OAM state is also analyzed.The proposed generators can be realized by all kinds of microwave transmission lines,verified by two different prototypes.The discussions and conclusions drawn in this study are useful and meaningful for the radio OAM generator design.     

一种多天线智能谱感知方法研究

频谱感知和多天线分集合并技术是目前无线通信研究的热点.为了在复杂的信道衰落环境下实施有效的检测,融合多种检测方法是目前频谱感知技术的发展趋势.提出了一种基于匹配滤波器检测、能量检测和循环平稳检测的多天线合并智能频谱感知算法.通过建立高斯信道下二元假设检验模型,得出了总检测概率的封闭表达式.各种条件下的检测概率和检测时间的接收机工作特性(Receiver Operating Characteristic,ROC)实验结果表明所提算法优于单天线的性能,有效地利用了分集技术并减小了信号瞬时波动,保证在衰落信道条件下也能得到较高的检测概率.这对发展新型频谱感知技术,促进认知无线电技术应用具有重要意义.     

Inverse design-based metamaterial transparent device and its multilayer realization

We propose an inverse method to determine the material parameters of a transparent device without any knowledge of the corresponding transformation function. The required parameters are independently obtained and expressed as functions of the introduced generator. Moreover, to remove the inhomogeneity and anisotropy of material parameters, a layered transparent device composed of only homogeneous and isotropic materials is presented based on the effective medium theory. The feasibility of using the layered device in antenna protection is also investigated. Full-wave simulation is carried out for verification. This work paves a new way toward designing metamaterial devices without specifying the underlying coordinate transformation, and has great guiding significance for the practical fabrication of transparent devices.     

气相色谱法测定电子烟烟液及气溶胶中双乙酰和乙酰丙酰

建立气相色谱法氢火焰离子化检测器测定电子烟烟液和气溶胶中双乙酰和乙酰丙酰含量的方法。样品以20 mL乙醇为萃取剂,涡旋振荡萃取10 min,采用气相色谱外标法进行定量分析。双乙酰和乙酰丙酰质量浓度在0.5~50 μg/mL范围内与色谱峰面积呈良好的线性关系,相关系数分别为0.999 6、0.999 4,方法检出限分别为0.044、0.052 μg/mL。烟液中双乙酰和乙酰丙酰测定结果的相对标准偏差为2.5%~4.3%(n=6),样品加标回收率为95.0%~102.5%;气溶胶中双乙酰和乙酰丙酰测定结果的相对标准偏差为3.1%~4.6%(n=6),样品加标回收率为92.7%~102.3%。气溶胶中双乙酰和乙酰丙酰理论浓度与实测浓度具有较强的相关性(对于双乙酰r~2=0.990 1,对于乙酰丙酰r~2=0.994 7),说明双乙酰、乙酰丙酰烟液通过雾化直接转移至气溶胶中。该方法准确度高,重现性好,检出限低,可满足电子烟样品的检测需求。     

基于变换热力学的任意形状热集中器研究与设计

如何灵活地控制和操纵热流是目前研究的热点.本文根据变换热力学方法,导出了具有任意横截面形状热集中器的材料参数表达式,并在此基础上设计了具有圆形、椭圆形、正五边形等规则横截面形状的热集中器和具有共形、非共形任意横截面形状的热集中器.全波仿真结果表明,这些热集中器使等温线和热通量向其压缩区弯曲,靠近热源的一侧热扩散加快而相反的一侧热扩散减慢,在很小的区域内表现出对热量的集中作用,这一特点在热能工程中有潜在应用.此外,研究了圆柱形热集中器的层化实现方法.结果显示,热集中器可通过将同性材料沿角向分层交替填充来实现.这项工作对热集中器的设计及制备具有指导意义.     

一种新型的电子烟雾化方法研究

针对电热式雾化电子烟存在核心专利受制于国外技术垄断、快速高热引发潜在安全健康风险、烟油接触雾化易烧结粘附等问题,该文基于声表面波(SAW)声流耦合效应,提出了一种新型的电子烟雾化方法,搭建了雾化系统实验平台,并采用成品烟油进行了雾化特性测试与分析。结果表明,系统能实现烟油非接触雾化,连续稳定地产生粒径小而分布均匀的气溶胶,且雾化速度快,功耗低,发热量小。研究验证了SAW雾化技术在电子烟中应用的可行性,是电子烟未来发展的一个新方向。     

Design of an optical device with three functions based on coordinate transformation

Based on two-step coordinate transformation along the radial direction, an optical device with three functions is proposed. The proposed device functions as a transparent device, a vision-enabling internal cloak, and a movement-allowing external cloak. The general expressions of material parameters for the optical device are determined, and each function of the device is confirmed using full-wave simulation. The effect of material loss on device performance is also investigated. Future applications for the proposed device include antenna protection and military stealth.     

一种新的超材料放大装置简化参数设计方法

超材料放大装置能够将物体任意放大,其在小目标识别和检测中有广泛的潜在应用。为了促进该装置的实际应用,基于变换光学原理提出了一种新的简化材料参数设计方法。该方法通过选择适当的变换方程,使得材料参数的径向和角向分量为常数而仅轴向分量随半径变化,同时还能确保装置的外边界与自由空间阻抗完全匹配。全波仿真结果验证了该方法的有效性和放大装置的良好性能。此外,分析了材料损耗和参数抖动对装置性能的影响,扩展了变换光学理论的应用,为超材料器件的参数简化提供了一种新的、可行的解决方案。