# Double-zero-index structural waveguides

## TL;DR

This paper demonstrates the design and experimental validation of a double-zero-index elastic waveguide that enables acoustic cloaking and supercoupling, using geometric tapers to induce Dirac-like cones and effective medium properties.

## Contribution

It introduces a novel double-zero-index elastic waveguide with experimentally verified cloaking and supercoupling effects, based on geometric tapers and Dirac-like cone induction.

## Key findings

- Successful experimental realization of double-zero-index waveguide
- Observation of cloaking and supercoupling effects
- Effective medium parameters confirmed through numerical analysis

## Abstract

We report on the theoretical and experimental realization of a double-zero-index elastic waveguide and on the corresponding acoustic cloacking and supercoupling effects. The proposed waveguide uses geometric tapers in order to induce Dirac-like cones at $\vec{k} = 0$ due to accidental degeneracy. The nature of the degeneracy is explored by a $k\cdot p$ perturbation method adapted to thin structural waveguides. Results confirm the linear nature of the dispersion around the degeneracy and the possibility to map the material to effective medium properties. Effective parameters, numerically extracted using boundary medium theory, confirm that the phononic waveguide maps into a double zero index material. Numerical and experimental results confirm the expected cloacking and supecoupling effects typical of zero index materials.