Sound Absorbing Acoustic Metamaterials using Helmholtz Resonators

The aim of this project is to garner a greater understanding of the coupling and critical coupling between multiple Helmholtz resonators and the role they play in sound absorbing acoustic metamaterials. The goal of this being to produce acoustic metamaterials that can achieve broadband, low frequency, sound absorption with sample thickness much less than that of the wavelength of sound absorbed.

This will be achieved through the following objectives:
Produce an analytical formulation that can be used to model the absorptive performance of coupled resonators in various configurations, whilst accounting for viscous and thermal energy losses.
Produce an optimization method, based upon the analytical model, that can be used as a powerful tool to tailor the absorptive performance of the coupled Helmholtz resonators by varying various geometrical parameters.
Produce numerical models that can be used to analyse the complex dispersion relationship of periodic arrays of coupled Helmholtz resonators. This will allow for the effect of losses to be understood when these systems of Helmholtz resonators are placed in periodic arrays.
Analyse the effect flowing media plays on the absorptive properties of acoustic metamaterials comprised of coupled Helmholtz resonators and integrate a term in to the previously established analytical model to account for this effect.

Application and benefits:
Typical sound absorbing materials used today, such as fibrous materials like rockwool, are woefully ineffective at absorbing low frequency sound. This is due to the mass-density law which dictates that a material must be either suitably dense or of comparable thickness to the wavelength of sound that is to be absorbed. This means that for low frequency sound, either heavy or thick sound absorbing materials is required to attenuate the sound. This is impractical for many engineering scenarios.

Acoustic metamaterials provide a way to absorb low frequency sound whilst being lightweight and at a sub-wavelength thickness. This project will provide a greater understanding of acoustic metamaterials consisting of Helmholtz resonators and will allow for more computationally inexpensive ways for systems of coupled resonators to be designed. Through this it will also provide a way for these systems to be optimised for acoustic performance whilst remaining within self-imposed geometrical constraints.

This research fits into the continuum mechanics EPSRC research area and is defined as metamaterials.