零压缩率波导中的声超耦合
Acoustic Supercoupling in a Zero-Compressibility Waveguide
摘要：
通过很大程度上失配的通道的有趣的声波对于针对各种应用定制和传输声音具有根本重要性。在电磁学中，零介电常数超材料已经被用来增强超窄通道的能量耦合，这种耦合基于一种被称为超耦合的现象。这些超材料通道可以支持总传输和完全相位均匀性，而与通道长度无关，尽管与它们的输入和输出端口几何失配。在声学领域，这种现象是具有挑战性的，因为它需要零密度的超材料，通常实现与波导周期性地加载膜或谐振器。与电磁学相比，额外的挑战是由于常规声波导不支持传播的主导模式的截止，因此零折射率只能基于加载元件的集体谐振来实现。在这里，我们提出并实验实现声学超耦合在一个双重制度，使用压缩性接近零的声学通道。而不是工程与亚波长夹杂物的通道，我们在一个高阶声学模式的截止操作，演示了实现和有效的激励的零压缩性波导与有效的软边界。我们通过实验验证强传输通过一个很大程度上失配的通道和均匀的相位分布，独立的通道长度。我们的研究结果打开了有趣的途径，实现极端的声学参数，并在相关的应用程序，如超声成像，声纳技术和声音传输中实现。
英文摘要：
Funneling acoustic waves through largely mismatched channels is of fundamental importance to tailor and transmit sound for a variety of applications. In electromagnetics, zero-permittivity metamaterials have been used to enhance the coupling of energy in and out of ultranarrow channels, based on a phenomenon known as supercoupling. These metamaterial channels can support total transmission and complete phase uniformity, independent of the channel length, despite being geometrically mismatched to their input and output ports. In the field of acoustics, this phenomenon is challenging to achieve, since it requires zero-density metamaterials, typically realized with waveguides periodically loaded with membranes or resonators. Compared to electromagnetics, the additional challenge is due to the fact that conventional acoustic waveguides do not support a cut-off for the dominant mode of propagation, and therefore zero-index can be achieved only based on a collective resonance of the loading elements. Here we propose and experimentally realize acoustic supercoupling in a dual regime, using a compressibility-near-zero acoustic channel. Rather than engineering the channel with subwavelength inclusions, we operate at the cut-off of a higher-order acoustic mode, demonstrating the realization and efficient excitation of a zero-compressibility waveguide with effective soft boundaries. We experimentally verify strong transmission through a largely mismatched channel and uniform phase distribution, independent of the channel length. Our results open interesting pathways towards the realization of extreme acoustic parameters, and their implementation in relevant applications, such as ultrasound imaging, sonar technology, and sound transmission.
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