Metamaterials Employed In Acoustics: Theoretical, Numerical And Experimental Analysis With Practical Application To The Case Of A Small
Household Appliance

Action 1.1.1 "Support for research projects to enterprises that involve

the employment of researchers (PhDs and master's graduates with technical-scientific profiles)

at the enterprises themselves.

DGR no.805 of June 11, 2019
Expenditure supported with the contribution of the Veneto Region 

Financial support received: € 154,440.00

Project Description.

Low noise has always been a valued quality for all types of household appliances, although technological improvement in the sector focuses on aspects related to energy saving and low environmental impact of materials. One of the limitations for the study of acoustic solutions applied to small household appliances is their compactness: manufacturing companies tend to make objects with the smallest possible footprint, making it difficult to incorporate additional materials aimed at containing noise. The goal of the project was to develop an effective yet small-sized sound-absorbing material. The acoustic innovation being industrially researched consists of the study of novel absorption systems: the "Metamaterials." They constitute an evolution of "Helmoltz resonators",differing from them for two reasons:

1) Selectivity: properly designed "Metamaterials" are capable of developing sound absorption,exactly in the frequencies with higher sound emissions.

2) "Metamaterials" are able to be effective but compact, thus ideal to be placed inside enclosures.



The sound-absorbing potential of metamaterial structures exhibited in the course R&D project, combined with the validated predictive reliability of the numerical methods that model their acoustic behavior, project this new type of sound-absorbing materials to be the ideal candidates to replace traditional sound-absorbing systems made of porous materials.
In the field of broadband sound absorption, particularly in the mid-to-high frequency region, the small dimensions of metamaterials , combined with the high average values of the absorption coefficient, are found to be suitable for the requirement of reduced volumetric footprint, which is often a design constraint, in the case of sound absorption problems of machinery (e.g., household appliances), for which the volumes available for housing sound-absorbing structures is significantly reduced and constrained by the presence of components from the highest design priority. Moreover, on the basis of the theoretical-speculative work, corroborated by empirical observation, conducted during the R&D course regarding metamaterials and, in general, cavity resonance sound-absorbing systems, the prospect of future insights about the combined use of metamaterials and microperforated materials is legitimate, either by coupling the microperforated layer with a backing structure of metamaterials or by the use of microholes in the guise of micro-slits, in order to be able to guarantee to the manufacturing reality the fulfillment of both acoustic (high sound-absorbing performance at both low and medium-high frequencies) and aesthetic requirements, especially required by applications for sound absorption in closed environments, in civil and construction.