Cholesteric elastomer waveguides doped with metallic nanospheres: exhibiting metamaterial-like behaviour under transverse elongation

The propagation of electromagnetic waves through a cholesteric elastomer slab doped with a small amount of randomly distributed metallic nanospheres, which is subjected to transverse elongation, is considered. The nanocomposite dielectric response formed by the cholesteric and the nanospheres is described using a Maxwell Garnett formalism. The real and imaginary parts of the dispersion relation are calculated numerically by solving Maxwell’s equations, subjected to the corresponding boundary conditions. The presence of two peaks in the imaginary part of the wave number of the hybrid system, caused by the plasmonic resonance of the metal, is observed. The group velocity versus frequency is also calculated, revealing two intervals where this quantity opposes the wave vector, giving rise to behaviour similar to that of a metamaterial waveguide. The behaviour is confirmed by the calculation of the Poynting vector, where the energy travels in the opposite direction to the wave vector.

考虑横向拉伸下，少量随机分布金属纳米球掺杂的胆甾相弹性体（cholesteric elastomer）薄板中电磁波的传播特性。由胆甾相材料与纳米球构成的纳米复合材料的介电响应采用麦克斯韦-加尼特形式（Maxwell Garnett formalism）描述。通过求解满足相应边界条件（boundary conditions）的麦克斯韦方程组（Maxwell’s equations），对色散关系（dispersion relation）的实部与虚部进行数值计算。观察到混合体系（hybrid system）波数（wave number）虚部存在两个峰值，这一现象由金属的等离子体共振（plasmonic resonance）引起。计算群速度（group velocity）随频率的变化关系，发现存在两个区间内群速度与波矢（wave vector）方向相反，呈现出类似超材料波导（metamaterial waveguide）的行为特征。通过坡印廷矢量（Poynting vector）的计算验证了上述行为——能量传播方向与波矢方向相反。