Abstract
Abstract The so-called locally resonant acoustic metamaterials (LRAMs) are a new kind of artificially engineered materials capable of attenuating acoustic waves. As the name suggests, this phenomenon occurs in the vicinity of internal frequencies of the material structure and can give rise to acoustic bandgaps. One possible way to achieve this is by considering periodic arrangements of a certain topology (unit cell), smaller in size than the characteristic wavelength. In this context, a computational model based on a homogenization framework has been developed from which one can obtain the aforementioned resonance frequencies for a given LRAM unit cell design in the sub-wavelength regime, which is suitable for low-frequency applications. Aiming at validating both the proposed numerical model and the local resonance phenomena responsible for the attenuation capabilities of such materials, a 3D-printed prototype consisting of a plate with a well selected LRAM unit cell design has been built and its acoustic response to normal incident waves in the range between 500 and 2000 Hz has been tested in an impedance tube. The results demonstrate the attenuating capabilities of the proposed design in the targeted frequency range for normal incident sound pressure waves and also establish the proposed formulation as the fundamental base for the computational design of 3D-printed LRAM-based structures.
Highlights
The notion of metamaterials as artificially engineered structures capable of exhibiting properties which cannot be found in ordinary materials has awoken the interest among both the scientific and industrial communities due to their potential applications [1]
A computational model based on a homogenization framework has been developed from which one can obtain the aforementioned resonance frequencies for a given Locally Resonant Acoustic Metamaterials (LRAM) unit cell design in the sub-wavelength regime, which is suitable for low-frequency applications
Among the first actual realizations of acoustic metamaterials, Liu et al [2] built a composite structure that possessed negative elastic constants, exhibiting bandgaps in localized regions of the frequency spectrum. Research in this line was followed by several other experimental demonstrations [5,6,7,8], in which the acoustic metamaterial consisted of a polymer-based matrix structure with embedded silicone rubber-coated metal inclusions
Summary
The notion of metamaterials as artificially engineered structures capable of exhibiting properties which cannot be found in ordinary materials has awoken the interest among both the scientific and industrial communities due to their potential applications [1]. Even though the concept was born in the context of electromagnetism, where materials behave as if they had negative refractive indices, the idea rapidly extended to other fields where wave propagation phenomena occur For this matter, in the context of acoustics, metamaterials show the ability to effectively stop waves from propagating in certain frequency ranges, typically called frequency bandgaps, due to local resonance effects [2]. Among the first actual realizations of acoustic metamaterials, Liu et al [2] built a composite structure that possessed negative elastic constants, exhibiting bandgaps in localized regions of the frequency spectrum Research in this line was followed by several other experimental demonstrations [5,6,7,8], in which the acoustic metamaterial consisted of a polymer-based matrix structure with embedded silicone rubber-coated metal inclusions. While most studies have been carried out on periodic arrangements, recent works show that irregularities and random structures exhibit attenuation capabilities and can even improve them with proper selection of certain parameters [18,19,20,21]
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