Spider web-structured labyrinthine acoustic metamaterials for low-frequency sound control

Attenuating low-frequency sound remains a challenge, despitemany advances in this field. Recently-developed acoustic metamaterials are characterized by unusual wave manipulation abilities thatmake themideal candidates for efficient subwavelength sound control. In particular, labyrinthine acoustic metamaterials exhibit extremely highwave reflectivity, conical dispersion, andmultiple artificial resonant modes originating fromthe specifically-designed topological architectures. These features enable broadband sound attenuation, negative refraction, acoustic cloaking and other peculiar effects. However, hybrid and/or tunablemetamaterial performance implying enhanced wave reflection and simultaneous presence of conical dispersion at desired frequencies has not been reported so far. In this paper,we propose a new type of labyrinthine acoustic metamaterials (LAMMs) with hybrid dispersion characteristics by exploiting spiderwebstructured configurations. The developed design approach consists in adding a square surrounding frame to sectorial circular-shaped labyrinthine channels described in previous publications (e.g. (11)).Despite its simplicity, this approach provides tunability in themetamaterial functionality, such as the activation/elimination of subwavelength band gaps and negative group-velocitymodes by increasing/decreasing the edge cavity dimensions. Since these cavities can be treated as extensions of variable-width internal channels, it becomes possible to exploit geometrical features, such as channelwidth, to shift the band gap position and size to desired frequencies. Time transient simulations demonstrate the effectiveness of the proposed metastructures for wavemanipulation in terms of transmission or reflection coefficients, amplitude attenuation and time delay at subwavelength frequencies. The obtained results can be important for practical applications of LAMMs such as lightweight acoustic barrierswith enhanced broadband wave-reflecting performances.