# Robust 3D multi-polar acoustic metamaterials with broadband double negativity

## TL;DR

This paper introduces a new class of robust 3D acoustic metamaterials with broadband double negativity, enabling practical subwavelength imaging in all directions through multi-polar resonances.

## Contribution

It proposes multi-cavity metamaterials with double-negative properties based on multi-polar resonances, overcoming symmetry and bandwidth limitations of previous designs.

## Key findings

- Achieved broadband subwavelength imaging with 2D and 3D superlenses.
- Discovered explicit relationships for double-negative frequency bounds.
- Demonstrated subwavelength imaging in all directions with 3D superlens.

## Abstract

Acoustic negative-index metamaterials show promise in achieving superlensing for diagnostic medical imaging. In spite of the recent progress made in this field, most metamaterials suffer from deficiencies such as low spatial symmetry, sophisticated labyrinth topologies and narrow-band features, which make them difficult to be utilized for symmetric subwavelength imaging applications. Here, we propose a category of robust multi-cavity metamaterials and reveal their common double-negative mechanism enabled by multi-polar (dipole, quadrupole and octupole) resonances in both two-dimensional (2D) and three-dimensional (3D) scenarios. In particular, we discover explicit relationships governing the double-negative frequency bounds from equivalent circuit analogy. Moreover, broadband single-source and double-source subwavelength imaging is realized and verified by 2D and 3D superlens. More importantly, the analogical 3D superlens can ensure the subwavelength imaging in all directions. The proposed multi-polar resonance-enabled robust metamaterials and design methodology open horizons for easier manipulation of subwavelength waves and realization of practical 3D metamaterial devices.

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Source: https://tomesphere.com/paper/1907.12101