A practically designed acoustic metamaterial sheet with two-dimensional connection of local resonators for sound insulation applications

Masanari Nakayama,Hiroshi Mitani,Yuya Saito,Shogo Koga,Kazuma Inoue,Shuichi Akasaka,Naoyuki Uchida,Takeshi Matsuoka

doi:10.1063/5.0041738

Masanari Nakayama, Hiroshi Mitani + Show 6 more

Open Access

https://doi.org/10.1063/5.0041738

Copy DOI

Abstract

A novel practical design of sheet-like acoustic metamaterials is described, which comprise a two-dimensional array of mutually connected cylindrical stubs with embedded metallic weights that can be processed with a simple integral molding. We investigate the elastic wave band dispersion of the acoustic metamaterial sheets to design the connected structure of the stubs so that each stub can work as spring–mass local resonators to open the out-of-plane acoustic bandgaps. For properly integrated materials, remarkable noise insulation performance over the mass law at the resonant frequencies is experimentally demonstrated. The sound insulation mechanism is numerically analyzed in association with the sound fields, the vibrational fields, and the dynamic effective mass using the finite element method by coupling the structures with acoustics. Furthermore, we show that the insulation frequency is tunable over a wide range of frequency by designing the physical and structural parameters of the resonator. The practically designed acoustic metamaterial sheets will pave the way for industrial use of acoustic metamaterials as advanced lightweight and compact sound insulators that can be tailored to meet individual needs on problems related to noise.

Highlights

For many years, it has been required to suppress undesirable mechanical vibrations and acoustic noise generated from automobiles, railways, airplanes, etc
We investigate the elastic wave band dispersion of the acoustic metamaterial sheets to design the connected structure of the stubs so that each stub can work as spring–mass local resonators to open the out-of-plane acoustic bandgaps
We have developed a new practical Acoustic metamaterials (AMMs) sheet with a 2D array of mutually connected spring–mass local resonators that can be mass-produced on a large scale through integral molding processes

Summary

Introduction

It has been required to suppress undesirable mechanical vibrations and acoustic noise generated from automobiles, railways, airplanes, etc. Acoustic metamaterials (AMMs) are artificially designed materials with extraordinary physical properties such as negative elastic constants, negative mass, or negative refractive index at certain frequency ranges.[1,2,3,4] The concept of metamaterials, which was originally studied for electromagnetic waves,[5,6,7] has expanded to acoustic/. AMMs having local resonance (LR) units assembled on a sub-wavelength scale with hard matrices give rise to acoustic bandgaps (BGs) around the resonant frequencies.[10–19]. They are typically composed of soft rubber and hard heavy materials that act as spring and mass parts for a spring–mass resonator, respectively, and interact with acoustic/elastic waves. The apparent effective mass scitation.org/journal/jap of the entire system is dynamically changed depending on the incident wave frequencies and is even divergent through the antiresonance mechanism.[20,21] Since acoustic BGs can prohibit acoustic/ elastic wave propagation within the materials and the materials behave as acoustic/elastic wave reflectors in the BG frequency range, the concept of AMMs will open the possibility of new design for soundproofing materials

Methods

Results

Conclusion