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Description
Locally resonant vibro-acoustic metamaterial panels have been shown to offer high sound transmission loss due to their stopband behaviour. Such treatments can significantly reduce the reradiation of sound energy in the stopband by reducing the local vibration of the panel. However, the increased transmission loss occurs over a narrow frequency band and is usually followed by a pronounced reduction in the transmission loss, hindering the broadband performance. This work proposes a metamaterial unit cell concept that combines mechanical and acoustical resonators to mitigate the dip in the transmission loss and thus enhance the overall transmission loss over a targeted frequency range. A numerical model of the coupled configuration is developed to gain insights into the structural and acoustical dynamics and their mutual interaction. A parametric study is performed to analyse the combined effects of the mechanical and acoustical resonator geometry on the transmission loss. Then, an optimisation procedure is implemented to obtain an optimal unit cell design for maximum attenuation. The numerical results indicate that the hybrid design can significantly reduce the minimum transmission loss while maintaining the stopband maximum, thus enhancing the broadband attenuation. The findings demonstrate that integrating mechanical and acoustical resonators within a unit cell offers a promising route toward compact, effective sound-insulating metamaterials.