Adaptive sound insulation of piezoelectric metastructure shells around ring and coincidence frequencies

To address the soundproof limitations of conventional shells around the ring and coincidence frequencies, this study proposes and investigates a locally resonant piezoelectric metastructure shell (meta-shell) for sound insulation. An electrical-mechanical-acoustic coupling model of the meta-shell is established using the planewave expansion method (PWEM). The sound transmission loss (STL) of the meta-shell is computed analytically and further validated through finite-element simulations. It is found that, under oblique incidence of sound waves, the meta-shell exhibits obvious enhancement of STL around the ring and coincidence frequencies when the piezoelectric shunting is properly tuned. The dispersion relations of elastic waves and sound waves are analyzed to elaborate the sound-insulation mechanism. Furthermore, it is demonstrated that the STL around the ring and coincidence frequencies can be improved simultaneously when the high-order resonant shunting circuits are introduced. Due to the high tunability of piezoelectric shuntings, the meta-shell could maintain superior sound-insulation performance under varying incidence angles of sound waves and Mach numbers of fluids, which inevitably lead to the shift of coincidence frequencies. It is not easy for mechanical meta-shells to adapt to such varying conditions. Overall, this research provides physical insights of sound insulation of locally resonant piezoelectric meta-shells, offering valuable guidance for designing smart acoustic skins of aircrafts.