摘要:
超材料慢声器件具有非常灵活的相位控制能力,能够实现超薄的声透镜、声学整流器和声学自加速发生器等多种声学功能器件.但是,大多数慢声器件存在严重的色散、界面阻抗不匹配等问题,限制慢声器件只能在较窄的带宽工作.文章介绍了一种全新的螺旋型慢声器件,回顾了均匀螺距的螺旋结构超材料和螺距连续变化的螺旋结构超材料,深入分析了实现宽带零色散慢声器件和宽带高耦合效率的慢声器件的基本原理和设计规则.这些慢声器件可通过调整结构的螺距来灵活实现相位调节.最后,文章从数值和实验两个方面证明了按照一定规律排列的螺旋结构型超材料单元可以将入射的平面声波转换成按预设抛物线轨迹传输的艾里声束.
Abstract:
Slow acoustic metamaterials are highly flexible systems for phase engineering applications.They have great potential in ultrathin acoustic devices,such as flat acoustic lenses,acoustic rectifiers,and self-accelerating beam generators.However,most slow acoustic metamaterials have serious dispersion and interface impedance mismatch and other problems.These defects restrict operation to a narrow bandwidth.To overcome this problem,novel helical-structured metamaterials may be used.We reviewed two helical-structures for implementing non-dispersive high effective refractive index slow acoustic devices and broadband impedance matching slow acoustic devices between two media with different impedances and cross section.We also provide some design guidelines,together with the basic principles.The performance characteristics of these devices may be tuned by varying the helicity of the structures.Finally,we demonstrate a self-accelerating beam on a prescribed parabolic trajectory using a one-dimension helical-structure metamaterial array with inhomogeneous cells.
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