Enhancing sound transmission loss of a piezoelectric metastructure shell in the low-frequency range using negative-capacitance shunting

To address the low-frequency sound insulation problem of shell structures, we explore and exploit a piezoelectric metastructure shell (meta-shell) with negative-capacitance (NC) shunting. The effective elastic parameters of the meta-shell are derived with considering the impacts of NC shunting, thereby enabling achieving its effective acoustic impedance for computing the sound transmission loss (STL). By configurating the piezoelectric shunting as such that the effective tensional rigidity of the meta-shell is increased, its ring frequency would be improved and therefore the low-frequency sound insulation performance below which is generally enhanced. Both the effective impedance method and the finite-element (FE) method are employed to analyze STL of the meta-shell. The sound transmission behaviors are further interpreted through dispersion relations of unit cells. It is found that, due to the increasing of rigidity, the two dispersion branches of the bending-tensional modes are overall shifted to higher frequency regimes through NC piezoelectric shunting. On the other hand, they are also separated far away in the frequency domain. It leads to quite distinct characteristic frequencies for sound waves with different incidence angles. Therefore, under the vertical incidence of sound waves, the low-frequency soundproof performance is enhanced much more significantly than that under the conditions with relatively large incidence angles. The scenarios with different values of negative capacitance, covering ratios and thickness ratios of piezoelectric patches are considered for comprehensively evaluating their impacts on the low-frequency soundproof performance of the meta-shell. Distinguished with metastructures relying on the local-resonance mechanism, the proposed scheme could improve sound insulation performance of shell structures in the broadband low-frequency range.