# Acoustical hooks: a new subwavelength self-bending beam

## TL;DR

This paper reports the discovery of a novel subwavelength self-bending acoustic beam with the smallest radius of curvature ever recorded, generated by vortices in a polymer immersed in water, with potential biomedical and particle manipulation applications.

## Contribution

It introduces a new type of near-field curved acoustic beam with subwavelength radius of curvature, generated through vortex-induced flow inside a solid, demonstrated via simulations and experiments.

## Key findings

- The acoustical hook has a radius of curvature less than the wavelength.
- The beam is generated by vortices inside the solid due to mode conversion.
- Potential applications include biomedical imaging and particle manipulation.

## Abstract

In this work, we report the observation of a new type of near-field curved acoustic beam different from the Airy-family beams both through simulations and experiment. This new self-bending acoustical beam is generate from a rectangular trapezoid of a polymer material immersed in water and has unique features. The radius of curvature of acoustical hook is less than the wavelength, it is represents the smallest radius of curvature ever recorded for any acoustical beams. The origin of this curved beam is in the vortices of intensity flow that appear inside the solid due to the conversion of the incident longitudinal wave mode to a shear wave in a solid. These vortices redirect the intensity flow, which causes the beam to bend. These results may be potentially useful when an object, that is in the path of the beam, must be avoid, such as in cancer treatments in which tumors are found behind bones such as ribs. It could also have potential applications in particle manipulations.

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Source: https://tomesphere.com/paper/1906.02148