共查询到19条相似文献,搜索用时 109 毫秒
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在获得石墨烯(RGO)/聚乳酸(PLA)、RGO/四氧化三铁(Fe3O4)/PLA多种复合吸波线材的基础上,利用熔融沉积成形技术打印了三层角锥吸波体。利用CST仿真与实验研究了吸波剂组合和分布方式(水平梯度分布和立体梯度分布)对角锥吸波性能的影响,并揭示了吸波机理。研究结果表明,对于均质吸波体,双组元吸波剂吸收性能更佳,且吸波性能随石墨烯的含量增加而改善;对于吸波剂梯度分布吸波体(此时锥体高度为16 mm,底面尺寸为10 mm×10 mm),立体梯度分布时(加入质量分数分别为3%、5%、7%的三层吸波剂石墨烯)可获得最强吸波效果:在6.1~18.0 GHz范围内的反射损耗低于-10 dB,有效吸波带宽可达11.9 GHz以上,在17.2 GHz处达到最高吸收强度为-45.8 dB;相对吸波剂组合,分布方式对角锥吸波能力具有更大影响,立体分布方式的吸波体一方面改善阻抗匹配特性,保证有效吸波带宽,另一方面增大多重散射、反射与球状衍射损耗,提高吸波强度。 相似文献
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设计了基于磁流变弹性体的超材料吸波器,该吸波器主要由硅橡胶和羰基铁粉构成.其中,在吸波器的制备阶段通过施加不同的磁场阵列形成不同的周期性结构单元,进而在不同的宏观结构和微观结构的共同作用下实现吸波特性.通过COMSOL软件仿真分析所设计吸波器的性能,然后制备相应的实物并进行测试.结果表明:反射损耗的实测结果与仿真结果基... 相似文献
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一种隐身目标电磁散射特性的计算方法 总被引:1,自引:1,他引:0
针对空空导弹无线电引信,用广义的雷达有效散射截面(CRCs)描述隐身目标近场散射特性.对覆盖吸波涂层的目标,以组合的三角形平面单元拟合目标的几何外形.利用物理光学法和物理绕射理论[1]计算目标每一单元的散射场和绕射场.考虑目标上的二次反射,计算无线电引信接收天线径上的目标电磁散射场.无线电吸波涂层目标的反射系数采用迭代方法计算,其方法可适用于具有任何类型电磁参数涂层的目标.以长空靶机和靶5目标为例,计算了其近场散射特性,为无线电引信设计提供参考依据.目标近场电磁散射特性的计算方法适用于隐身目标和非隐身目标. 相似文献
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涡旋电磁波具有独特螺旋状波前结构,其受目标横向微动调制产生的旋转多普勒效应,有望为雷达目标探测技术的发展提供一个新途径。在涡旋电磁波照射下,利用锥体微动对回波瞬时频率的周期性调制特性,可以有效反演出锥体目标的微动参数和几何特征。该文重点研究了雷达前视条件下的锥体目标参数估计。首先,基于涡旋电磁波雷达目标旋转多普勒探测原理,推导了涡旋电磁波锥体目标回波数学方程,建立了锥体目标回波旋转多普勒模型。其次,提出了前视条件下的锥体目标参数估计方法,利用锥顶散射点和锥底散射点两维的旋转多普勒信息,可以对锥体目标微动参数和几何特征参数进行有效估计,仿真结果验证了该文所提方法的有效性及抗噪声鲁棒性。 相似文献
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针对主动雷达导引头对防空导弹武器系统制导雷达站检测与识别的需求,研究了平面隙缝阵列天线的宽带电磁散射特性.将天线的电磁散射机理与目标高频散射中心理论相结合,建立了天线的电磁散射模型,分别采用矩量法和物理光学法计算天线的模式项散射场和结构项散射场,并从理论上证明了天线散射中心的客观存在,分析了隙缝阵列天线的散射中心分布特征.最后对不同视角下天线的高分辨距离像进行了仿真,为进一步理解天线的电磁散射机理、分析其宽带电磁散射特性、以及采用高分辨率成像技术对雷达站进行检测与识别奠定了基础. 相似文献
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陶院高青松段福伟丁成斌金铭 《微波学报》2019,35(2):69-74
基于周期性阵列角锥结构星载微波辐射热定标源,运用时域有限差分算法(Finite Difference Time Domain,FDTD),建立有限大辐射体电磁波散射模型,探索该结构下热定标源在6.3~230 GHz 内辐射特性变化趋势,分析热定标源辐射性能(包括反射率r和发射率e)随涂层厚度t、角锥高宽比以及角锥宽度p 的变化规律。研究结果表明:热定标源反射率在低频段主要依赖涂层吸波性能,高频段则主要取决于涂层界面反射率;在低频段内,随涂层厚度的增加,热定标源反射率逐渐减小,发射率有所增大,但在高频处,呈现出较快的震荡趋势;在特定涂层厚度下,随着角锥高宽比增加,热定标源在全工作频段内反射率减小,发射率增大,且随着角锥宽度的增加,反射率增大,发射率减小。综合热定标源辐射性能研究结果,结合型号产品具体应用需求,设计开发出热定标源产品,并进行发射率测量,实测发射率均为0.998。 相似文献
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Electromagnetic scattering from periodic structures can be formulated in terms of an integral equation that has as its kernel a periodic Green's function. The periodic Green's function can be derived as a response to an array of line/point sources (spatial domain) or as a response to series of current sheets (spectral domain). These responses are a Fourier transform pair and are slowly convergent summations. The convergence problems in each domain arise from unavoidable singularities in the reciprocal domain. A method is discussed to overcome the slow convergence by using the Poisson summation formula and summing in a combination of spectral and spatial domains. A parameter study is performed to determine an optimum way to weigh the combination of domains. simple examples of scattering from a one-dimensional array of strips and two-dimensional array of plates are used to illustrate the concepts 相似文献
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本文提出一种基于稀疏编码的多核学习图像分类方法.传统稀疏编码方法对图像进行分类时,损失了空间信息,本文采用对图像进行空间金字塔多划分方式为特征加入空间信息限制.在利用非线性SVM方法进行图像分类时,空间金字塔的各层分别形成一个核矩阵,本文使用多核学习方法求解各个核矩阵的权重,通过核矩阵的线性组合来获取能够对整个分类集区分能力最强的核矩阵.实验结果表明了本文所提出图像分类方法的有效性和鲁棒性.对Scene Categories场景数据集可以达到83.10%的分类准确率,这是当前该数据集上能达到的最高分类准确率. 相似文献
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Ji Young Kim Guicheng Liu Ga Young Shim Hansung Kim Joong Kee Lee 《Advanced functional materials》2020,30(36)
Here, an electrode comprising a Zn hexagonal pyramid array (HPA) coated with a functionalized ZnO layer (Zn@ZnO HPA) is prepared using a periodic anodizing technique. The HPA structure markedly increases the electroactive surface area of Zn anode, thus decreasing the local current density. Furthermore, the functionalized ZnO coating layer has a gradient thickness that plays an important role in the selective deposition of Zn ions and the mitigation of side reactions at the interface. The electrochemical stability of the Zn@ZnO HPA electrode, which is closely related to the electroactive surface area and charge transfer resistance, is determined by the “split” value, i.e., ratio of current‐off to current‐on time, a parameter of the periodic anodizing process. Compared with the pristine Zn‐based symmetric cell, the Zn@ZnO HPA‐based symmetric cell is safely operated in the investigated experimental range with the 10‐fold improved running life and 25‐fold enhanced current density without Zn dendrite growth. Moreover, the Zn@ZnO HPA/MnO2 battery exhibits outstanding long‐term cyclability (nearly 100%) with greater than 99% Coulombic efficiency after 1000 cycles at a current density of 9 A g?1. This periodic anodizing technique for ultrastable Zn metal anodes is expected to contribute to the development of inherently safe energy storage systems. 相似文献
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N. N. Faleev A. Yu. Egorov A. E. Zhukov A. R. Kovsh S. S. Mikhrin V. M. Ustinov K. M. Pavlov V. I. Punegov M. Tabuchi Y. Takeda 《Semiconductors》1999,33(11):1229-1237
Multilayer InAs-GaAs structures with an array of vertically aligned InAs quantum dots in a GaAs matrix, grown by molecular-beam
epitaxy, were investigated by crystal truncation rods and high-resolution x-ray diffractometry methods. It was shown that
the formation of scattering objects such as vertically aligned quantum dots in the structures strongly influences the mechanism
of diffraction scattering of x-rays and changes the spatial distribution of the diffracted radiation. This is explained by
the appearance of additional long-range order in the lateral arrangement of the scattering objects in the periodic structures,
by the curving of the crystallographic planes in the periodic part of the structure, and by the quasiperiodicity of the deformation
profile due to the vertically coupled quantum dots. The observed spatial distribution of the diffracted intensity can be explained
qualitatively on the basis of a new model where the scattering layers with quantum dots consist of defect-free, coherently
coupled, InAs and GaAs clusters.
Fiz. Tekh. Poluprovodn. 33, 1359–1368 (November 1999) 相似文献
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A family of Schur-type spatial least-squares algorithms is presented for solving the spatial LS estimation problem, in which the correlation matrix is neither Toeplitz nor near-Toeplitz, by order recursion. Normalized spatial Levinson- and Schur-type algorithms are also derived. Highly pipelined architectures are designed to realize these recursions. The reflection coefficients are first computed using the spatial Schur type recursions. Then, the forward and backward filter parameters are calculated by the spatial Levinson-type recursions. A pyramid systolic array is demonstrated to calculate not only the filter parameters but also the LDU decomposition of the inverse cross-correlation matrix at every clock phase. This pyramid array can be mapped onto a two-dimensional systolic array which has a simpler structure. A square systolic array is developed to implement the Levinson- and Schur-type temporal recursive LS (RLS) algorithms. A highly concurrent architecture which exploits the parallelism of the spatial Schur-type recursions is illustrated to perform the LDU decomposition of the cross-correlation matrix 相似文献
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基于对比度塔形分解(CP)的图像融合方法具有良好的物理意义,却没有强调方向性的不足,为此提出了一种具有方向性的对比度金字塔图像融合方法.对多聚焦图像进行对比度塔形分解,利用方向滤波器组对高频加方向,得到不同方向的高频子分量.根据不同频率域特点,采用低频分量系数取加权平均、高频分量系数绝对值取大的融合规则,对分解后的子图像进行融合.结果表明:用提出方法得到的融合图像有较高的清晰度和空间分辨率.与基于CP和基于离散小波变换(DWT)的融合方法相比,提出的方法既能保持对比度的含义,又可提供2n个方向信息. 相似文献
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一种车载对数周期阵列天线的结构设计 总被引:1,自引:1,他引:0
对车载对数周期阵列天线(LPDA)结构设计方案进行了详细论述。阵列天线整体外形成四棱锥状,由4个对数周期天线单元按同一角度阵列而成,每个对数周期天线单元的集合线作为四棱锥的四条棱。使用Pro/E对其进行了实体造型,对空间阵列天线关键部件进行了静力分析。为了验证其安全性,对其强度和刚度进行校核,在此基础上完成了空间阵列天线的结构设计。阵列天线工作可靠,结构紧凑,便于车载拆装,很好地满足了预期的使用性能要求。 相似文献
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四元数小波变换在图像处理中的应用 总被引:1,自引:0,他引:1
根据四元小波理论提出了一种新的参数估计方法,用于估计刚体在空间的旋转位置。该方法将四元代数理论与小波变换相结合,推导出基于多分辨率分析的四元小波金字塔。金字塔将二维图像映射到四维空间,其每个层次提供3个相位,利用相位与图像变化之间的线性关系估计空间差距和旋转角度,实现一个自上而下的有效参数估计,从而推广了小波变换的应用。通过物体旋转检测程序对旋转前后的图像进行处理,得到空间变换趋势,证明该理论的可行性。 相似文献