超被动边界的声学Willis超材料
Acoustic Willis metamaterials beyond the passivity bound
摘要：
声学双各向异性，也被称为威利斯参数，通过在本构关系中提供动量和应变之间的非常规耦合来扩展声学领域。共享与电磁学的共同点，声学双各向异性的实现使得能够与适当设计的逆体积模量和质量密度合作来操纵声波。虽然整个本构参数的控制证实了有趣的理论和实际应用，威利斯超材料，使独立和精确设计的极化率尚未开发，以克服目前的限制的最大威利斯约束和非互易性固有的超材料的无源性。在这里，通过扩展最近开发的虚拟超材料的概念，我们提出了声学威利斯超材料，打破了被动性和互易性的限制，同时也实现了解耦控制的所有本构参数与设计的频率响应。通过建立基础卷积核的奇偶对称性的基础上为每个偏振响应，我们实验证明了双各向异性超出了被动介质的限制。此外，通过数字卷积的频率色散的逆设计的概念的基础上，纯非互易介质和介质的宽带，平坦响应威利斯耦合也证明。我们的方法提供了所有可能的独立可编程的极端本构参数和频率色散可调谐性的因果关系条件内访问，并提供了一个灵活的平台，实现声学超材料的全部功能。
英文摘要：
Acoustic bianisotropy, also known as the Willis parameter, expands the field of acoustics by providing nonconventional couplings between momentum and strain in constitutive relations. Sharing the common ground with electromagnetics, the realization of acoustic bianisotropy enables the exotic manipulation of acoustic waves in cooperation with a properly designed inverse bulk modulus and mass density. While the control of entire constitutive parameters substantiates intriguing theoretical and practical applications, a Willis metamaterial that enables independently and precisely designed polarizabilities has yet to be developed to overcome the present restrictions of the maximum Willis bound and the nonreciprocity inherent to the passivity of metamaterials. Here, by extending the recently developed concept of virtualized metamaterials, we propose acoustic Willis metamaterials that break the passivity and reciprocity limit while also achieving decoupled control of all constitutive parameters with designed frequency responses. By instituting basis convolution kernels based on parity symmetry for each polarization response, we experimentally demonstrate bianisotropy beyond the limit of passive media. Furthermore, based on the notion of inverse design of the frequency dispersion by means of digital convolution, purely nonreciprocal media and media with a broadband, flat-response Willis coupling are also demonstrated. Our approach offers all possible independently programmable extreme constitutive parameters and frequency dispersion tunability accessible within the causality condition and provides a flexible platform for realizing the full capabilities of acoustic metamaterials.
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