Ziolkowski Richard W, Kipple Allison D
Department of Electrical and Computer Engineering, The University of Arizona, 1230 E. Speedway Boulevard, Tucson, Arizona 85721-0104, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Aug;68(2 Pt 2):026615. doi: 10.1103/PhysRevE.68.026615. Epub 2003 Aug 29.
The causality of waves propagating in a double-negative (DNG) metamaterial (epsilon (r)<0 and mu(r)<0) has been investigated both analytically and numerically. By considering the one-dimensional electromagnetic problem of a pulsed current sheet radiating into a DNG medium, it is shown that causality is maintained in the presence of a negative index of refraction only if the DNG medium is dispersive. A Drude model DNG medium is used in this study. Spectrograms of the wave phenomena in the dispersive DNG medium show that the higher frequency components, which create the leading edge of the electromagnetic signals and see a double positive (DPS) medium (epsilon (r)>0 and mu(r)>0), arrive causally before the negative index effects germinate completely. Comparisons with approximate analytical results demonstrate the presence of the negative index of refraction properties in the continuous wave portion of the signals. This dynamic pulse reshaping between the positive and negative index of refraction wave components causes an apparent delay in the realization of the negative index of refraction properties. Pulse broadening of the signal tails is associated with both dispersion and a larger negative index of refraction seen by the associated wave components.
对在双负（DNG）超材料（ε(r)<0且μ(r)<0）中传播的波的因果关系进行了分析和数值研究。通过考虑脉冲电流片辐射到DNG介质中的一维电磁问题，结果表明，只有当DNG介质具有色散特性时，在存在负折射率的情况下因果关系才能得以维持。本研究中使用了德鲁德模型DNG介质。色散DNG介质中波现象的频谱图表明，产生电磁信号前沿且视为双正（DPS）介质（ε(r)>0且μ(r)>0）的较高频率成分，在负折射率效应完全显现之前就因果性地到达了。与近似分析结果的比较证明了信号连续波部分中负折射率特性的存在。正、负折射率波分量之间的这种动态脉冲重塑导致负折射率特性的实现出现明显延迟。信号尾部的脉冲展宽与色散以及相关波分量所观察到的更大负折射率都有关。
