Hierarchical metamaterials with tunable flat bands, zero-frequency, and wavenumber gaps

TL;DR

This paper introduces a tunable hierarchical metamaterial capable of exhibiting multiple exotic wave control features such as flat bands, zero-frequency, and wavenumber gaps, with tunability achieved through magnetic boundary adjustments.

Contribution

It presents a novel design of passive hierarchical metamaterials with tunable dispersion properties, combining analytical, numerical, and experimental validation.

Findings

Successfully demonstrated tunable wavenumber band gaps

Achieved complete flattening of dispersion bands

Confirmed zero-frequency band gaps through experiments

Abstract

Metamaterials are arrangement of basic building blocks that repeat in space, time, or both. These material systems serve as an excellent platform for controlling waves, such as engineering wavenumber band gaps, flat bands, and zero-frequency band gaps. However, combining one or more of these exotic features within the same unit cell design remains a challenge. Moreover, once a metamaterial is realized, its dispersive properties are usually fixed. In this work, we present a tunable passive hierarchical metamaterial capable of exhibiting wavenumber band gaps, flat bands, and zero-frequency band gaps within the same dispersion curve. Our metamaterial is composed of magnetic elements confined within a fixed magnetic boundary. The metamaterial can be tuned by adjusting the magnetic boundary, which in turn can alter the lattice periodicity. We open wavenumber band gaps by incorporating magnetic coupling within the unit cell elements, resulting in negative physical stiffness. The tunability of the magnetic coupling also enables complete flattening of the dispersion bands. Moreover, the ground stiffness within our unit-cell design causes the opening of zero-frequency band gaps. We present our approach through a combination of analytical, numerical, and experimental methods. The analytical framework provides a blueprint for obtaining each of these exotic dispersion characteristics. The numerical analysis, using both linear and nonlinear models, validates our analytical predictions, which we further confirm through experimental demonstrations. Our work opens the door to exploring magnetic tunability and hierarchy in engineering metamaterial systems with exotic properties that can be harnessed in advanced acoustic and mechanical devices.