Acoustic higher-order topological insulators (AHTIs) hosting topological corner states provide a promising way for the robust localization of acoustic waves. However, energies of prior corner states are localized within a limited area, restricting their applications in the large-area localization of acoustic waves. Meanwhile, despite the critical importance of operating frequency for acoustic device performance, precisely engineering corner states at a specific frequency with a fixed lattice constant remains a challenge. Here, we theoretically propose and experimentally demonstrate an acoustic sandwich metastructure that hosts large-area corner state (LACS) with desired eigenfrequencies by inserting Dirac material layers within two topologically distinct domains. The spatial decay mechanism of LACS is revealed via complex band theory. The frequency of LACS can be finely tuned by modulating the frequency of Dirac material layers via a developed topology optimization algorithm. Furthermore, by spatially separating LACSs with distinct frequencies, we achieve the rainbow LACSs. Our work offers a route to designing AHTIs with tailored LACSs, thereby achieving large-area acoustic trapping with frequency-multiplexed and reconfigurable capabilities.

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• Acoustic wave phenomena
• Symmetry protected topological states
• Topological effects in acoustic systems
• Acoustic metamaterials
• Dirac semimetal
• Multilayer thin films
• Topological insulators