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本文设计了一种能够对机械波进行吸收的超材料梁,超材料梁由若干质量-弹簧微结构系统和一根各向同性梁构成.通过对两种不同结构的质量-弹簧系统的分析,从理论上解释了"负有效质量"和"负有效刚度".根据Hamilton原理,导出了超材料梁的代表性胞元的控制方程.通过数值模拟分析了两种不同结构的有限超材料梁对机械波的吸收性能,一种是弹性系数线性变化的质量-弹簧系统在有限梁内均匀分布,另一种是由固有频率线性变化的弹簧-阻尼器子系统构成四个相同吸收器子群在有限梁内均匀分布.模拟结果表明,进入梁中的机械波与质量-弹簧振子
关键词:
超材料梁
负有效质量
负有效刚度
机械波 相似文献
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对金银复合纳米颗粒的去极化光谱进行了理论计算和研究。研究结果表明:金银复合纳米颗粒去极化光谱具有单峰的特征。在不同能量光照下,其介电常数是不同的,所以其去极化光谱也是变化的,然而其峰值总是介于纯金和纯银纳米颗粒去极化峰值之间,并且随着金银复合纳米颗粒中银体积分数的增加,去极化峰位于449~268nm附近,即近乎线性蓝移,峰形为高斯型,半高宽在514~324nm范围内近乎线性的减小。这说明可以通过控制入射光的能量和金银的组分来可控的改变金-银复合纳米颗粒的去极化光谱。 相似文献
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对于电小厚度的平面分层介质,在电磁波垂直入射情况下,根据边界条件把中间层介质等效为一层得到了有效介电常量和有效磁导率的表达式,为分析电磁波在多层介质中的传播问题提供了一种有效方法. 相似文献
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基于麦克斯韦旋度方程, 将磁电超材料板中的电元件和磁元件分别等效为面电流和面磁流, 通过计算这些周期性面电流和面磁流在某个磁电超材料板上产生的总电场和总磁场, 获得了关于面磁流密度和面电流密度的两个方程, 进而推导出了周期性磁电超材料折射率与磁元件的磁导率、 电元件的介电常数和空间色散项之间关系的解析公式. 与传统的折射率计算公式不同, 该解析公式充分考虑到了空间色散以及磁电超材料的电元件和磁元件的相互作用. 折射率理论曲线和基于仿真实验数据的提取值曲线能很好地符合, 这说明文中推导的折射率公式能够正确地描述磁电超材料的负折射特性. 本文的结果将为分析电磁元件之间的相互作用以及设计负折射率符合一定要求的磁电超材料提供重要的理论参考.
关键词:
磁电超材料
周期性结构
负折射率 相似文献
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为增强晶体硅太阳电池的光利用效率,提高光电转换效率,研究了金属银纳米颗粒的光学散射性质.基于银纳米粒子表面等离子激元效应和MIE散射理论,采用Matlab数值计算,理论分析了不同银纳米颗粒尺寸和银粒子分布密度对太阳光谱各波长的散射特性.获得了实现高的光透过率所需最佳银纳米颗粒半径范围,研究发现随着银纳米颗粒半径增加,偶极峰红移、高极峰逐渐出现.定量地给出了最佳颗粒分布密度随银粒子半径的变化规律,建立了计算减反射膜透射率的理论方法,找到了银纳米颗粒光学透过率的简单函数表达式,能为实验研究提供理论指导.
关键词:
银纳米颗粒
透过率
MIE理论
太阳电池 相似文献
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通过分子动力学模拟对聚乙烯/银纳米颗粒复合物的结构、极化率和红外光谱、热力学性质、力学特性进行计算, 分析其随模拟温度和银颗粒尺寸的变化规律. 模拟结果表明: 聚乙烯/银纳米颗粒复合物为各向同性的无定形结构, 温度升高可提高银纳米颗粒的分散均匀性; 银纳米颗粒表面多个原子层呈现无定形状态, 并在银颗粒和聚乙烯基体的界面形成电极化层, 界面区域随颗粒尺寸和温度的增加分别减小和增加; 与聚乙烯体系相比, 聚乙烯/银纳米颗粒复合物的极化率高很多, 且随温度的升高和银颗粒尺寸的减小而增大; 银颗粒尺寸直接影响界面电偶极矩的强度和振动频率, 红外光谱峰强度和峰位随颗粒尺寸发生变化; 聚乙烯/银纳米颗粒复合物具有比聚乙烯体系更高的等容热容和与聚乙烯体系相反的负值热压力系数, 热容随颗粒尺寸的变化较小, 但随温度的升高而明显减小, 具有显著的温度效应; 热压力系数随温度的变化较小, 但随颗粒尺寸的增加而减小, 具有明显的尺度效应, 温度稳定性更好; 聚乙烯/银纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量, 具有比聚乙烯体系更高的杨氏模量和泊松比, 并且都随温度的升高和银颗粒尺寸的增大而减小, 加入银纳米颗粒可有效改善聚乙烯的力学性质.
关键词:
分子动力学模拟
聚合物纳米复合物
纳米颗粒 相似文献
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采用双槽电化学腐蚀法以电阻率为10-15 Ω·cm的p型<100>晶向的单晶硅片制备了孔径约为1.5 μm, 孔深约为15-20 μm的p型多孔硅, 并以此多孔硅作为基底采用无电沉积法通过调控沉积时间在其表面沉积了不同厚度的银纳米颗粒薄膜. 采用扫描电子显微镜和X 射线衍射仪表征了银纳米颗粒/多孔硅复合材料的形貌和微观结构, 结果表明银纳米颗粒较均匀的分布于多孔硅的表面上且沉积时间对产物的形貌有重要影响. 采用静态配气法在室温下研究了银纳米颗粒/多孔硅复合材料对NH3的气敏性能. 气敏测试结果表明沉积时间对产物的气敏性能影响较大. 当沉积时间较短时, 适量银纳米颗粒掺杂的多孔硅复合材料由于其较高的比表面积以及特殊的形貌和结构, 对NH3气体表现出较高的灵敏度、优良的响应/恢复性能. 室温下, 其对50 ppm 的NH3气体的气敏灵敏度可以达到5.8左右. 相似文献
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采用分子动力学方法和嵌入原子法(EAM)多体势函数,模拟研究了银纳米团簇在不同温度直到熔化过程中的结构变化,得到了体系能量和热容量随温度的变化关系.结果显示:银纳米团簇在临近熔点附近出现了负热容现象.研究了弛豫后银纳米团簇的稳态结构变化及其在不同时刻结构的演变过程.结果表明:产生负热容现象的主要原因是纳米团簇在熔点附近,结构发生了巨大的变化,形成由{111}和{100}面围成的结构十分稳定和能量更低的多面体. 相似文献
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F. Gadot B. Belier A. Aassime J. Mangeney A. de Lustrac J.-M. Lourtioz 《Optical and Quantum Electronics》2007,39(4-6):273-284
Periodic arrays of gold wires and split ring resonators (SRR) with a minimum feature size of 50 nm are fabricated on low-doped
silicon. To our knowledge, the periodic arrangement of SRRs and wires considered in this work has not been studied in the
near-infrared domain yet. For normal-incidence conditions, this metamaterial structure exhibits resonances at 70 and 170 THz
(i.e., at λ ≈ 4.3 and 1.75 μm), which are identified as LC- and Mie resonances, respectively. These resonances are also observed for the SRRs alone, but
the amplitude of the Mie resonance is reinforced due to the coupling between the SRRs and wires. The structure is simulated
using finite-element software, while transmission and reflection measurements are performed with a Fourier transform infrared
spectrometer. Numerical simulations are found to be in very good agreement with experimental characterizations, thereby showing
that the Drude model used in calculations is well suited to simulate gold structures at near-infrared frequencies. Theoretical
calculations predict that the metamaterial has a negative permittivity and a negative permeability near each resonance. 相似文献
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农产品质量安全是社会广泛关注的重大民生问题.近年来,农产品生产过程中农药的广泛使用和滥用会导致农药残留,对人类健康和环境造成潜在危害.吡虫啉是一种硝基亚甲基类新烟碱内吸杀虫剂,因其具有广谱、高效和低毒的特性已广泛用于农业生产中,但其过量残留也给人类的健康带来了威胁.首先对超材料结构的透射谱进行了分析,对共振频率的形成原... 相似文献
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Possibilities to realize a negative refraction in chiral composites in dual-phase mixtures of chiral and dipole particles are studied. It is shown that because of a strong resonant interaction between chiral particles (helices) and dipoles, there is a stop band in the frequency area where the backward-wave regime is expected. The negative refraction can occur near the resonant frequency of chiral particles. Resonant chiral composites may offer a root to realization of negative-refraction effect and superlenses in the optical region. 相似文献
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The dispersive characteristics of surface plasmon polaritons (SPPs) supported by a periodically corrugated boundary between vacuum and a negative refractive index, isotropic material were studied theoretically by numerical solution of a dispersion equation. SPP dispersion curves were correlated with the optical response of the corrugated boundary in frequency regions where SPPs can be excited by a normally incident plane wave. Abrupt reflectivity variations, characterized by the presence of a near unity maximum and an almost zero minimum, were found in regions where the boundary without corrugation exhibits low reflectivity and rather featureless reflectivity curves. 相似文献
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Philippe Tassin Thomas Koschny Costas M. Soukoulis 《Physica B: Condensed Matter》2012,407(20):4062-4065
An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media. 相似文献
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Experimental study of composite medium with simultaneously negative permeability and permittivity 总被引:1,自引:0,他引:1
SUI Qiang & LI Fang . Institute of Electronics Chinese Academy of Sciences Beijing China . School of Information Beijing Broadcasting Institute Beijing China Correspondence should be addressed to Sui Qiang 《中国科学G辑(英文版)》2004,47(1):64-78
Inclassicalelectrodynamics,theresponse(typicallyfrequencydependent)ofamaterialtoelectricandmagneticfieldsischaracterizedbytwofundamentalquantities,thepermittivityeandthepermeabilitym.Bothmandearepositiveinmostmaterials.In1968,Veselago[1]predictedthattheelectromagneticwavepropagationinamediumhavingsimultaneouslynegativepermittivityandpermeabilityshouldgiverisetoseveralpeculiarcharacteristics.Butnoneofhispredictionsweretestedduringthelastcentury,becausenonaturalmaterialswithsimultaneouslynegativ… 相似文献
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Akhlesh Lakhtakia 《International Journal of Infrared and Millimeter Waves》2002,23(3):339-343
The canonical problem of a perfect lens with linear bianisotropic materials is formulated. Its solution is shown to be directly connected with the concept of nihility, the electromagnetic nilpotent. Perfect lenses as well as nihility remain unrealizable. 相似文献
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采用离子交换结合热处理的方法在碱石灰玻璃表面制备了银纳米颗粒。通过紫外-可见分光光度计、X射线衍射仪、扫描电子显微镜对样品进行了表征。结果表明:热处理时,银离子在玻璃表面成核并生长成近似长方形的纳米颗粒。吸收光谱在416nm附近出现明显的银纳米颗粒表面等离子体共振吸收特征峰。 相似文献