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1. Visco-elastic effects on wave dispersion in three-phase acoustic metamaterials
This study analyzes wave attenuation performance of dissipative solid acoustic metamaterials with local resonators characterized by subwavelength band gaps. The metamaterial is composed of dense rubber-coated inclusions of a circular shape embedded periodically in a matrix medium. Visco-elastic material losses present in a matrix and/or resonator coating are introduced by either the Kelvin–Voigt or generalized Maxwell models. Numerical solutions are obtained in the frequency domain by means of k(ω)-approach combined with the finite element method. Spatially attenuating waves are described by real frequencies ω and complex-valued wave vectors k. Complete 3D band structure diagrams including complex-valued pass bands are evaluated for the undamped linear elastic and several visco-elastic acoustic metamaterials. The changes in the band diagrams due to the visco-elasticity are discussed in detail; the comparison between the two visco-elastic models representing artificial, Kelvin–Voigt model, and experimentally characterized, generalized Maxwell model, damping is performed. The interpretation of the results is facilitated by using attenuation and transmission spectra. Two mechanisms of the energy absorption, i.e. due to the resonance of the inclusions and dissipative effects in the materials, are discussed separately. We found that the visco-elastic damping of the matrix material decreases the attenuation performance of metamaterials within band gaps; however, if the matrix material is slightly damped, it can be modeled as linear elastic without the loss of accuracy given the resonator coating is dissipative. This study also demonstrates that visco-elastic losses properly introduced in the resonator coating improve the attenuation bandwidth of acoustic metamaterials although the attenuation on the resonance peaks is reduced (source).
This research has been done in collaboration with the group of Prof. M. Geers in Eindhoven University of Technology, the Netherlands.
2. The attenuation performance of locally resonant acoustic metamaterials based on generalised viscoelastic modelling (link)
Acoustic metamaterials are known as a promising class of materials interacting with acoustic and/or elastic waves. Band gap formation is one of the most spectacular phenomena that they exhibit. Different ways to broaden the attenuated frequency ranges are still being actively explored. It turns out that material damping through intrinsic viscoelastic material behaviour, if accurately tailored, may contribute to the enhancement of the performance of a properly designed acoustic metamaterial. In this study, a locally resonant acoustic metamaterial with periodic multicoated inclusions with viscoelastic layers is investigated. Multiple attenuation regimes obtained with the considered geometry are joined for a certain level of viscosity of the coating layer. The analysis is performed using a generalised Maxwell model, which allows for an accurate description of nonlinear frequency dependent elastic properties, and thus is widely used to model the behaviour of many polymeric materials in a realistic way. The study reveals that variation of the material parameters of the rubber coating with respect to frequency influences not only the position of the band gaps but also the effectiveness of the wave attenuation in the frequency ranges around the band gaps (source).
This research has been done in collaboration with the group of Prof. M. Geers in Eindhoven University of Technology, the Netherlands.
3. Structure-independent viscoelasticity of phononic materials
This work presents a review of wave propagation properties in dissipative elastic metamaterials including phononic materials and locally resonant acoustic metamaterials. We show that the induced dissipative effects are solely governed by the material viscoelasticity and are the same for all metastructures regardless of their composition and wave attenuation mechanisms. The derived conclusions are validated by an excellent agreement with experimental data (available on demand).
This research has been done in collaboration with the groups of Prof. N. Pugno, University of Trento, and Prof. M. Scalerandi, Politecnico University of Turin, in Italy.
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