loss factor

phononic crystals

transmission loss

sound absorption

resonant frequency

auxetic metamaterials

band gaps

phononic crystal

Journal of sound and vibration

Vibro-acoustic locally resonant metamaterials with structural stop band behaviour can lead to a strongly increased sound transmission loss in a targeted frequency range. This work assesses the impact of damping in the constituents of metamaterial plates on their acoustic insulation performance by means of infinite periodic and finite structure modelling. Besides applying the hybrid Wave Based - Finite Element unit cell method for infinite plates and the Finite Element Method for finite plates, qualitative dispersion curve based predictions are extended to quantitative sound transmission loss approximations by introducing a dispersion curve based equivalent plate method. Both an idealised and a realisable locally resonant metamaterial plate are analysed. Damping in the resonators in particular is found to have an important impact in and around the stop band, reducing the sound transmission loss peak, but improving the subsequent dip and reducing resonant transmission in a broadening frequency range around the stop band. The damping influenced sound transmission loss predictions for the realisable locally resonant metamaterial plate are experimentally validated by means of insertion loss measurements. It is shown that, by including damping in the infinite periodic structure modelling, acoustic insulation performance predictions with improved accuracy are obtained. • The impact of damping on the STL of locally resonant metamaterial plates is analysed. • The damping influenced STL of infinite and finite metamaterial plates is compared. • A dispersion curve based equivalent plate method for STL approximations is proposed. • The damping influenced infinite plate STL predictions are experimentally validated.

The impact of damping on the sound transmission loss of locally resonant metamaterial plates