Synthesis of anisotropic swirling surface acoustic waves by inverse filter, towards integrated generators of acoustical vortices

TL;DR

This paper introduces a novel inverse filter method with SAW transducer arrays to generate complex swirling surface acoustic waves, including acoustical vortices, for advanced applications in sensing and micromanipulation.

Contribution

It presents a flexible, inverse filter-based approach for synthesizing complex, anisotropic swirling surface acoustic waves, including acoustical vortices, which were previously unavailable.

Findings

Successful synthesis of 2D acoustical vortices with phase singularities

Demonstration of complex wave pattern generation on anisotropic media

Potential applications in contactless micromanipulation and sensing

Abstract

From radio-electronics signal analysis to biological samples actuation, surface acoustic waves (SAW) are involved in a multitude of modern devices. Despite this versatility, SAW transducers developed up to date only authorize the synthesis of the most simple standing or progressive waves such as plane and focused waves. In particular, acoustical integrated sources able to generate acoustical vortices (the analogue of optical vortices) are missing. In this work, we propose a flexible tool based on inverse filter technique and arrays of SAW transducers enabling the synthesis of prescribed complex wave patterns at the surface of anisotropic media. The potential of this setup is illustrated by the synthesis of a 2D analog of 3D acoustical vortices, namely "swirling surface acoustic waves". Similarly to their 3D counterpart, they appear as concentric structures of bright rings with a phase singularity in their center resulting in a central dark spot. Swirling SAW can be useful in fragile sensors whose neighborhood needs vigorous actuation, and may also serve as integrated transducers for acoustical vortices. Since these waves are essential to fine acoustical tweezing, swirling SAW may become the cornerstone of future micrometric devices for contactless manipulation.