Observation of acoustic Dirac-like cone and double zero refractive index.
Observation of acoustic Dirac-like cone and double zero refractive index.
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DOI：
10.1038/ncomms14871
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发表时间：
2017-03-20
影响因子：
16.6
通讯作者：
Zhang X
中科院分区：
文献类型：
--
作者：
Dubois M;Shi C;Zhu X;Wang Y;Zhang X
零折射率材料是一种无相位变化的声传播材料，在波阵面和色散工程中具有很大的应用潜力。最近发现的电磁双零折射率超材料由折射率显著大于周围介质的周期性散射体组成。这一要求对空气声学来说是一个根本性的挑战，因为空气中的声速（与折射率成反比）是最慢的。在这里，我们报告的第一个实验实现的阻抗匹配声学双零折射率的超材料诱导的狄拉克锥在布里渊区中心。这是在具有周期性变化的空气通道的二维波导中实现的，该空气通道调制高阶波导模式的有效相速度。利用这种零折射率介质，我们演示了从点源发射的声波准直。我们首次从实验上证实了布里渊区中心的类狄拉克锥的存在。声学超材料和周围介质之间的阻抗失配阻碍了有效的应用，特别是对于零折射率材料。在这里，Dubois等人利用双零折射率材料中的Dirac-like色散来克服这个问题并准直声音。
Zero index materials where sound propagates without phase variation, holds a great potential for wavefront and dispersion engineering. Recently explored electromagnetic double zero index metamaterials consist of periodic scatterers whose refractive index is significantly larger than that of the surrounding medium. This requirement is fundamentally challenging for airborne acoustics because the sound speed (inversely proportional to the refractive index) in air is among the slowest. Here, we report the first experimental realization of an impedance matched acoustic double zero refractive index metamaterial induced by a Dirac-like cone at the Brillouin zone centre. This is achieved in a two-dimensional waveguide with periodically varying air channel that modulates the effective phase velocity of a high-order waveguide mode. Using such a zero-index medium, we demonstrated acoustic wave collimation emitted from a point source. For the first time, we experimentally confirm the existence of the Dirac-like cone at the Brillouin zone centre. Impedance mismatch between acoustic metamaterials and a surrounding medium hinders efficient applications, especially for zero-index materials. Here, Dubois et al. utilize the Dirac-like dispersion in a double-zero-index material to overcome this problem and to collimate sound.