Broadband low-frequency sound insulation of a sandwich acoustic metamaterial with coupled-resonance

To broaden the bandwidth, a sandwich acoustic metamaterial with periodically rib-stiffened cores is presented by incorporating strip masses. The normal sound transmission loss of the structure is predicted using the finite element method. Results indicate that the two attenuation peaks are coupled, which is validated by the impedance tube experiment. The primary mechanism of the coupled-resonance is attributed to the continuous non-zero effective dynamic surface mass density between two anti-resonances. The conditions for generating the coupled-resonance are derived based on the dual mass-spring model without resolving the matrix eigenvalues. Numerical verifications suggest that the coupled band will break down into two isolated narrow bands if the conditions fail.