Graded negative index lens with designable focal length by phononic crystal

TL;DR

This paper presents a flat, graded negative index phononic crystal lens capable of focusing and amplifying acoustic waves, with a design formula enabling precise focal length customization and aberration reduction.

Contribution

It introduces a novel flat lens with a graded negative refractive index using phononic crystals, including a design method for specific focal lengths and minimized aberrations.

Findings

Successfully demonstrated focusing and amplification of acoustic waves.

Derived a formula for designing lenses with specific focal lengths.

Achieved reduction of image aberrations.

Abstract

We realize a flat lens with graded negative refractive index by a two-dimensional phononic crystal. The index-grade is achieved by gradual modification of the filling fraction along the transverse direction to propagation. We demonstrate that this lens can realize the focusing and amplification of parallel incident acoustic waves. A formula for the refractive index profile is derived by which the lens with desired focal length can be precisely designed and the aberrations of image can be effectively reduced. This designable lens is expected to bear significance in applications such as coupling or integration with various types of acoustic devices.