Abstract
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 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.
Highlights
In electromagnetism and photonics, high index dielectric particles are becoming an important platform to study novel physical phenomena [1]
Sources such as the Huygens and Janus dipoles show interesting directional scattering and coupling characteristics, both in the far field and in the near field [4, 5], and they have been experimentally demonstrated in high-index nanoparticles [6,7,8,9] with interfering electric p and magnetic m dipole moments
In the near-field, directional coupling of waveguided modes was initially predicted and demonstrated in electromagnetism via the evanescent coupling of circularly polarised dipoles [13], relying on the transverse spin and spin-momentum locking in evanescent waves [14,15,16]
Summary
High index dielectric particles are becoming an important platform to study novel physical phenomena [1]. A high index dielectric particle can exhibit strong magnetic Mie resonances [2, 3] that are of comparable strength to the electric ones Sources such as the Huygens and Janus dipoles show interesting directional scattering and coupling characteristics, both in the far field and in the near field [4, 5], and they have been experimentally demonstrated in high-index nanoparticles [6,7,8,9] with interfering electric p and magnetic m dipole moments. In this work we explore the possibility to produce acoustic Huygens and Janus-type directional sources to achieve far and near-field directionality, using a high-index particle platform
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