Sound insulation characteristic of triangular-lattice hierarchical sonic crystals

Environmental noise, particularly traffic noise, has been identified as a major contributor to health issues, necessitating effective solutions of sound insulation. Sonic crystals (SCs) have been studied as potential materials that provide sound insulation while maintaining ventilation. However, SCs have problems such as partial sound bandgap (SBG) bandwidth, anisotropic sound insulation properties and the necessity of large structures for low-frequency control, limiting their practical applications. In this study, sound insulation properties of two-dimensional triangular-lattice hierarchical sonic crystals (HSCs), in which a hierarchical structure is applied to SCs were examined by the finite element method. The results show that incorporating multiple lattice constants enables the formation of SBGs corresponding to each lattice constant. Also, the second-order SBGs of HSCs exhibit isotropy, suggesting a potential solution to the incident angle dependency of conventional SCs. This isotropic SBG property enhances the applicability of SCs as sound insulation materials in architectural and urban environments. These findings highlight the effectiveness of hierarchical structures in SCs and provide valuable insights into their potential for advanced acoustic applications.