Acoustic metamaterials : microperforated shell and Helmholtz resonator

Metamaterials have been extensively developed in many areas over the past two decades, a great deal of research has been conducted on acoustic metamaterials exhibiting unusual dynamic effective material properties produced by artificially engineered microstructures. While most of the studies are still scattered, superficial delineations and lack of effective practical application. To promote the application of metamaterials, we designed the structures to explore the metamaterials application in acoustic wave modulation where these techniques can be used to reduce to noise inside the structure and ensure the safety of the target. Acoustic metamaterials have been studied intensively recently since they can expose unnatural-born properties, potentially breaking the capacity limits of conventional acoustic materials. Since these interesting properties are mostly observed around metamaterials' local resonances/anti-resonance, resonance-based acoustic metamaterials are most popular in developing metamaterials. Employing resonance-based unnatural born properties such as effective negative mass density, effective negative bulk modulus, and acoustic hyper-damping on designing noise control solutions can give excellent devices showing such high performance that conventional acoustic material cannot achieve. This dissertation is an effort to employ acoustic metamaterials in designing efficient noise control. Helmholtz has been used to design a high-performance and broadband acoustic silencer. Specifically, five slit-type Helmholtz resonators, which possess a massive viscous area, are packed together to create a single-layer silencer. In turn, two single-layer silencers are combined to form a double-layer silencer, which in theory double performance on noise blocking of the single-layer silencer. Theoretical models of slit-type Helmholtz resonators and silencers are developed completely and well validated with simulation and experimental results.