Far-field directional scattering and near-field directional coupling from simple sources have recently received great attention in photonics: beyond circularly-polarized dipoles, whose directional coupling to evanescent waves was recently applied to acoustics, the near-field directionality of modes in optics includes phased combinations of electric and magnetic dipoles, such as the Janus dipole and the Huygens dipole, both of which have been experimentally implemented using high refractive index nanoparticles. In this work we extend this to acoustics: we propose the use of high acoustic index scatterers exhibiting phased combinations of acoustic monopoles and dipoles with far-field and near-field directionality. All solutions stem from the elegant acoustic angular spectrum of the acoustic source, in close analogy to electromagnetism. A Huygens acoustic source with zero backward scattering is proposed and numerically demonstrated, as well as a Janus source achieving face-selective and position-dependent evanescent coupling to nearby acoustic waveguides.

中文翻译：

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声散射中的远场和近场方向性

来自简单源的远场定向散射和近场定向耦合最近在光子学中受到了极大的关注：除了圆极化偶极子，其与渐逝波的定向耦合最近被应用于声学，光学中模式的近场定向性包括电偶极子和磁偶极子的定相组合，例如 Janus 偶极子和惠更斯偶极子，这两者都已使用高折射率纳米粒子通过实验实现。在这项工作中，我们将其扩展到声学：我们建议使用高声学指数散射体，表现出具有远场和近场方向性的声学单极子和偶极子的相位组合。所有解决方案都源于声源的优雅声学角谱，与电磁学非常相似。