# Three-dimensional acoustic double-zero-index medium with a Dirac-like point

## TL;DR

This paper presents the design and experimental validation of a 3D acoustic double-zero-index medium that behaves like a void space, enabling novel sound manipulation applications such as an acoustic periscope.

## Contribution

The authors introduce a novel 3D DZIM constructed from a cubic lattice of metal rods, demonstrating its properties and potential for advanced acoustic wave control.

## Key findings

- Successful fabrication of a 3D DZIM with near-zero effective parameters
- Observation of wave tunneling with undisturbed wavefront in a 3D waveguide
- Realization of an acoustic periscope using the DZIM

## Abstract

We report a design and experimental realization of a three-dimensional (3D) acoustic double-zero-index medium (DZIM), whose effective mass density and compressibility are nearly zero simultaneously. The DZIM is constructed from a cubic lattice of three orthogonally-aligned metal rods in air. The combination of lattice symmetry and accidental degeneracy yields a four-fold degenerate point with conical dispersion at the Brillouin zone center, where the material becomes a 3D DZIM. Though occupying a finite volume, the 3D DZIM maintains the wave properties of a "void space," and enables rich applications. For demonstration, we fabricate an acoustic "periscope" by placing the designed 3D DZIM inside a 3D bending waveguide, and observe the unusual wave tunneling effect through this waveguide with undisturbed planar wavefront. Our findings establish a practical route to realize 3D DZIM as an effective acoustic "void space," which offers unprecedented opportunities for advanced sound manipulation.

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Source: https://tomesphere.com/paper/1901.08830