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Broadband and high efficiency terahertz metasurfaces for anomalous refraction and vortex beam generation 下载免费PDF全文
The applications of metasurfaces are currently a highly active research field due to their extraordinary ability to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices work typically under a low efficiency and narrow bandwidth condition. In this work, we design eight multilayered unit cells with similar amplitudes and a phase interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitudes of these cells are all around 0.9 in an ultra-broad frequency range from 0.5 THz to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical prediction, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and more. The distributions of longitudinal electric field, intensity, and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement in the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that are applied to other frequency ranges. 相似文献
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根据本征方程,研究磁电弹性体中若干平行螺型位错与Griffith裂纹的相互作用.结合Muskhelishvili方法和算子理论,得到磁电弹性体中由位错和裂纹所诱导的应力场、电场和磁场的解析解.数值算例表明:在裂纹的端点及位错点上仍然存在应力的奇异性,离位错点越远处广义力越小,结论与已有的结果相符,证明了结论的正确性.当位错点与裂纹端点距离越近时,裂纹与位错间的应力场越小,并逐渐趋近于零. 相似文献
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<正>1引言Burgers方程可以作为描述许多物理现象的数学模型,如交通流、激波、扰流问题和连续的随机过程.它还可以用于检验数值方法的效率.由于其具有较广的实用范围,一些学者对其近似解进行了较多的研究.如Adomian分解方法、混合有限差分和边界元方法、样条有限元方法、精确显式有限差分方法、Douglas有限差分格式,直接变分方法和变分迭代方法被用于Burgers方程近似解的研究~([1-13]).Hopf-Cole变换~([14,15])是研究Burgers方程较好的分析工具,利用它可以获得Burgers方程一些精确解.近年来,人们意识到该变换也是一个很好的数值工具并利用其得到了一 相似文献
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利用太赫兹时域光谱技术测量了聚乙烯、聚丙烯、聚氯乙烯、聚四氟乙烯和丙烯腈-丁二烯-苯乙烯的太赫兹透射谱,研究其在0.2~2.6 THz频段的光谱特性,得到了在室温氮气环境下这些材料的太赫兹吸收谱和折射率色散特性.发现这五种塑料在太赫兹波段的折射率和吸收系数差异显著,折射率分别在1.35~1.85之间,聚乙烯、聚丙烯、聚四氟乙烯吸收很小,相比之下聚氯乙烯、丙烯腈-丁二烯-苯乙烯吸收很大,这为塑料种类的鉴别及高太赫兹透过率塑料衬底选择提供了依据. 相似文献
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This paper considers the one-dimensional dissipative cubic nonlinear Schrödinger equation with zero Dirichlet boundary conditions on a bounded domain. The equation is discretized in time by a linear implicit three-level central difference scheme, which has analogous discrete conservation laws of charge and energy. The convergence with two orders and the stability of the scheme are analysed using a priori estimates. Numerical tests show that the three-level scheme is more efficient. 相似文献
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对一类四阶微分方程两点边值问题的Hermite有限元方法进行了研究.首先讨论了该方程通常意义下的Galerkin有限元离散,考虑到有限元离散得到的线性方程组的对称正定性,文中采用了预处理最速下降法和共轭梯度方法求解线性方程组,通过选择不同的预处理器,使得求解该方程组的迭代次数有了很大的改观. 相似文献
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This paper applies the variational iteration method to obtain approximate analytic solutions of compressible Euler equations in gas dynamics.This method is based on the use of Lagrange multiplier for identification of optimal values of parameters in a functional.Using this method,a rapid convergent sequence is produced which converges to the exact solutions of the problem.Numerical results and comparison with other two numerical solutions verify that this method is very convenient and efficient. 相似文献