共查询到18条相似文献,搜索用时 140 毫秒
1.
流动隐身衣因为可以显著降低指定目标的表面阻力而备受关注.然而大多数传统流动隐身衣的设计参数为非均匀各向异性,非均匀这一限制增加了制备流动隐身衣的难度.为突破这种限制,本文采用等效介质理论与积分中值定理,将流动隐身衣所需的设计参数均匀化.通过数值模拟验证了简化后的均匀流动隐身衣具有与非均匀流动隐身衣一样的隐身效果,并且同样适用于多种流场.这种简化方法不仅可以将非均匀流动隐身衣简化为均匀流动隐身衣,更重要的是可以适用于其他领域,如光学、声学、电磁学与热学等不同领域的超材料均匀化设计,为降低超材料制备难度提供了新方法.此外,基于均匀流动隐身衣对不同流场的适用性,首次设计了一种流动伪装装置,该装置可以将原始物体所产生的流场伪装成由任意物体引起的期望流场,为实现流动伪装提供了解决方案.最后,定量对比分析了流动隐身衣的隐身与减阻性能随着雷诺数增加的变化,结果表明在非蠕动流时流动隐身衣仍然具有良好的隐身性能与较高的减阻效率. 相似文献
2.
3.
4.
5.
基于多层复合材料结构的二维声隐身斗篷设计思想, 利用主动隔膜声学空腔有效密度可以任意控制这一特性, 设计了主动声学超材料下的无限长圆柱声隐身斗篷. 给出了主动隔膜声学空腔单元的声电元件类比模拟电路图和具体的有效密度控制方法. 进行了主动声学超材料声隐身斗篷的结构建模, 并对平面入射波入射下此圆柱隐身斗篷周围声压分布场进行仿真计算. 结果表明, 平面波在一定频率范围内可以毫无阻碍地透过圆柱斗篷, 似乎不存在这种障碍物, 达到声隐身效果. 同时, 计算了主动声材料斗篷下总散射截面随频率变化曲线, 研究了此斗篷隐身效果随频率的变化特性. 本文从主动控制角度探讨实验实现隐身斗篷的技术问题, 有望给声隐身斗篷实验设计提供一条新的技术途径. 相似文献
6.
7.
由于超材料的微结构尺度不能忽略,利用超材料微结构所集成的器件等效参数不是连续分布的,而是呈离散分布的。因此在利用超材料设计声学器件的过程中,需要对器件进行分层离散化,而分层方案的选取往往会影响器件的工作效果。该文基于五模材料水下隐身衣的设计理论,提出了一种基于遗传算法的五模材料隐身衣分层优化策略,并分别对优化前和优化后的分层隐身衣做了声学仿真。仿真结果表明采用优化策略后,隐身衣背景声场的散射能量和反射能量均有大幅度降低,并且对窄带探测信号和宽带探测信号均有较好的隐身效果,因此该分层优化策略能够显著提升隐身衣的隐身效果。该文所提出的分层优化策略为提升五模材料隐身衣性能提供了理论支持,并可以进一步推广至其他超材料器件的微结构设计中。 相似文献
8.
9.
从古代道家的隐身符到哈利波特的隐身衣,人类对隐身“超能力”的追求古老又神秘。而从隐身飞机到隐身舰船,社会对隐身技术的需求既强烈又实际。现代科技的发展给了我们信心,隐身不只是一种“超能力”,而是一种实实在在的技术。下面我们就一起来解读一下现有的各类“隐身术”。在谈隐身之前首先要知道为什么我们能看见物体。从光学角度来讲,当空间中的光照射到物体表面时,物体会向各个方向散射(包括了反射和透射)不同颜色(波长或频率)的光波。这些散射光进入人的眼睛后,会在视网膜上呈现出各种形状、颜色的像。简而言之,我们通常是通过接收物体的散射光来探测物体的。 相似文献
10.
人工局域表面等离激元结构具有许多特殊的光学性质,对于新一代光学元件的设计具有重要的意义.本文设计了一种在硅盘中周期性嵌入金属条的结构,从而使得物体在任意方向的光散射均被抑制,实现了全方向隐身的效果.通过理论分析与数值模拟,发现这种空心的人工局域表面等离激元结构在一定频率下会出现强散射抑制现象,这是由结构的散射波与背景波之间干涉相消产生的效果,且由于结构是一种周期性环状结构,因此可以在散射抑制的频率点下实现全方向的隐身效果.这为分析人工局域表面等离激元结构的物理隐身和光学响应提供了一条新的途径.此外,本文还分析了结构在不同参数条件下对散射谱移动规律的影响.本文的结果适用于微波到太赫兹波区域,可以应用于各种先进的光学器件,如雷达、隐身涂层、传感器和探测器等. 相似文献
11.
Based on the effective medium theory, the triangular ground plane cloak can be realized by thin layered systems. Two solutions of parameter setting of the layered cloak are suggested to demonstrate the invisibility performance of a hybrid incoming wave. The hybrid parameters are derived from the equivalent of both anisotropies of permittivity and permeability to the alternating layers. The performance of the designed layered cloak is validated by both TM and TE wave simulations with near-field distributions and average scattering power outflows on an observation semicircle. From the simulation results, the layered cloak with both hybrid parameters and improved hybrid parameters can reflect the incoming TM/TE waves in a specular direction, and the latter behaves with a better overall invisibility performance. 相似文献
12.
Acoustic carpet invisibility cloak with two open windows using multilayered homogeneous isotropic material 下载免费PDF全文
We present a method for designing an open acoustic cloak that can conceal a perturbation on flat ground and simultaneously meet the requirement of communication and matter interchange between the inside and the outside of the cloak. This cloak can be constructed with a multilayered structure and each layer is an isotropic and homogeneous medium. The design scheme consists of two steps: firstly, we apply a conformal coordinate transformation to obtain a quasi-perfect cloak with heterogeneous isotropic material; then, according to the profile of the material distribution, we degenerate this cloak into a multilayered-homogeneous isotropic cloak, which has two open windows with negligible disturbance on its invisibility performance. This may greatly facilitate the fabrication and enhance the applicability of such a carpet-type cloak. 相似文献
13.
Improving the performance of acoustic invisibility with multilayer structure based on scattering analysis 下载免费PDF全文
In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section. 相似文献
14.
研究基于蜷曲空间结构的近零折射率声聚焦透镜.根据近零折射率材料的声波方向选择机理,采用蜷曲空间结构为基本单元进行排列,设计具有特定入射与出射界面的几何结构,对透射声波的出射方向进行调控,实现了平面声波与柱面声波的聚焦效应,并深入讨论了透镜内部刚性散射体对声聚焦性能的影响.在此基础上,改变近零折射率透镜的出射界面,可以精确调控声波阵面的形状与方向.该类型透镜具有单一的单元结构、高聚焦性能及高鲁棒性等优点.研究结果为设计新型近零折射率声聚焦透镜提供了理论指导与实验参考,同时也为研究声波阵面的调控提供了新思路. 相似文献
15.
A three-dimensional (3D) spherical acoustic cloak is designed using an acoustic layered system, which can hide an object from
the detection of acoustic wave in arbitrary direction. The cloak is constructed from multilayered concentric spherical shells
filled with homogeneous isotropic materials. Based on spherical wave expansion method, we confirm that significant low-reflection,
acoustic-shadow-reducing, and wavefront-bending effects in 3D space can be achieved by the proposed cloak. The angle distribution
of the scattered wave is further evaluated by the far-field scattering pattern. In addition, the cloak is demonstrated to
work efficiently in a wide bandwidth in which the cloaking efficiency decreases with increasing frequency. This study may
be helpful to design high-performance 3D acoustic cloaks for broadband acoustic waves in all incidence directions. 相似文献
16.
17.
Due to the correspondence of the acoustic equations to Maxwell??s equations of one polarization in two dimensions, we exploit theoretically the acoustic counterpart of the recently proposed remote invisibility cloak. The cloak consists of a circular cylindrical core with designed bulk moduli, and an ??anti-object?? embedded inside a shell with anisotropic mass densities. The material parameters of the cloaking shells are obtained by using the coordinate transformation method. The essence of the new design of cloaks relies on the ability that the cloaked object is no longer deafened by the cloaking shell, which is verified by both the far-field and near-field full-wave finite-element simulations in two dimensions. 相似文献