A triply periodic minimal surface-based acoustic crystal with double-zero index

Three-dimensional (3D) acoustic crystals (ACs) with a double-zero index exhibit unique properties akin to a 3D void space, enabling transformative applications in acoustic wave cloaking, tunneling, and wavefront shaping. However, existing 3D ACs with a double-zero index are all made of disconnected solid structures, posing significant fabrication challenges for diverse applications. Here, we propose a fabrication-friendly triply periodic minimal surface (TPMS)-based AC with a double-zero index, resulting from a Dirac-like cone accidentally degenerated by three dipolar modes and one monopolar mode. The exotic functionalities of acoustic wave tunneling and cloaking characterized by the double-zero index are experimentally demonstrated. Meanwhile, the tunable mechanical properties of the TPMS-based AC are exhibited. The developed TPMS-based AC overcomes the fabrication limitations of conventional 3D double-zero-index acoustic structures while providing superior mechanical performance, paving the way for the development of multifunctional acoustic devices.