The effects of core negative stiffness on sound transmission loss of composite sandwich panels

Abstract

Metamaterials can significantly enhance the sound insulation properties of composite panels at low frequencies. This study investigates the impact of negative stiffness metamaterials on the acoustic performance of composite panels at frequencies below 1000 Hz. Utilizing the Finite Element (FE) Method, the quasi-static behavior and sound transmission loss (STL) in a proposed flat composite panel incorporating a negative stiffness core are studied. To characterize the core's behavior, its stiffness has been analyzed under various compression levels. Subsequently, by applying an initial pressure to the core structure, the core is subjected to negative stiffness conditions, and its effect on the STL behavior of the panel is examined. The study encompassed an evaluation of the effects of compression-induced deformation and stress changes within the core on acoustic performance. The STL behavior in the proposed sandwich panel is compared with a well-known hexagonal honeycomb core, maintaining identical mass and dimensions. Results demonstrate that compressing the panel with a negative stiffness core, reduces resonance regions in the STL spectrum, leading to a significant enhancement in sound insulation across a broad frequency range. The proposed design exhibited an improvement in STL of approximately 25 dB, therefore, this method integrates new capabilities into composite structures.