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• Sandwich panels with structural cores exhibiting bandgaps are studied. • Impact of acoustic transmission path on sound transmission is investigated. • STL, mode contributions to STL and dispersion curves are investigated. • Including both structural and acoustic paths in analysis is shown to be crucial. In the search for lightweight and compact structures with favorable vibro-acoustic performance, periodic structures such as phononic crystals and locally resonant metamaterials have shown potential. Recently, these periodic structures are included between two panels in a sandwich configuration to combine the interesting vibro-acoustic performance of the core with the potential load-carrying capacity of the sandwich configuration. During the design and numerical analysis of the vibro-acoustic performance of these structures, commonly only the structural connection between the plates is considered. However, next to the structural connection, also an acoustic transmission path is present between the plates of the sandwich configuration in reality. Because of this, the promising performance due to the structural decoupling of the double panel configuration by the bandgap behavior of the periodic core predicted with the analyses only considering the structural connection, are often not attained in experimental measurements. In this work, the impact of the ignored acoustic transmission path on the sound transmission loss of sandwich panels with structural periodic cores which exhibit bandgap behavior, is investigated. It is shown that the sound transmission follows the path of least resistance. Therefore, it is crucial to consider both the structural as the acoustic path in the partitions during the design phase to correctly predict the vibro-acoustic performance of these novel sandwich panel configurations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, a wide variety of inhomogeneous periodic structures including locally resonant metamaterials and phononic crystals have come to the fore in the search for innovative noise and vibration solutions which are lightweight and compact. With the often intricate design of these periodic cells, noise and vibration attenuation is achieved in targeted frequency ranges, called stopbands. The vibro-acoustic performance of these structures is mostly analyzed using unit cell modeling, by means of dispersion curves and/or sound transmission loss (STL) calculations. Although several techniques exist to compute the dispersion curves and/or STL, the link between these two performance indicators is often not straightforward, especially for increasingly complex unit cell designs, which can make their analysis and design cumbersome. To bridge this gap and come to a thorough understanding of these periodic structures, a method to rank the wave modes of the dispersion curves contributing to the sound transmission is required. Recently, a first step towards such an approach has been developed using a wave and finite element method (Yang et al., 2021). However, that technique is limited to in-plane homogeneous structures which can be represented by meshes with corner degrees-of-freedom only. To be able to investigate the relation between the STL and the dispersion curves of inhomogeneous (vibro-acoustic) periodic structures which require larger, and arbitrary complex meshes, this wave and finite element based methodology needs to be extended. Therefore, this work proposes a new methodology which addresses the current limitations. Several numerical case studies demonstrate the ability of the proposed methodology to bridge the gap between dispersion curves and STL calculations. • Existing method to compute wave mode STL contributions extended to periodic media. • Numerically stable wave mode decomposition method for large meshes is proposed. • Methodology is applicable for arbitrary, complex (vibro-acoustic) meshes. • Method demonstrated for idealized and practical engineering periodic cases. • Limitations and guidelines to verify the validity of the methodology are derived. [ABSTRACT FROM AUTHOR]