Broadband absorption of low-frequency sounds using acoustic metasurface based on multiple hybrid resnances

Abstract

Acoustic materials or acoustic structures have been widely used as solutions for the sound absorption and sound insulation problems in various industries. When conventional acoustic materials or structures are used, their thickness must inevitably be thick for low-frequency sound absorption because the thickness must be similar to the incident wavelength. Recently, in order to overcome the limitations of existing acoustic materials or structures, research on sound-absorbing structures using acoustic metamaterials or metasurfaces with subwavelength scales has been actively conducted. Subwavelength Helmholtz resonators are the resonant structures widely used in the metasurface design because they are structurally solid and easy to fabricate via three-dimensional printing technology. Since the acoustic path inside the resonator is very small compared to the wavelength, the effects of visco-thermal losses plays an important role. In this study, we propose an acoustic metasurface for generating hybrid resonance between adjacent resonators at a target frequency. For the proposed acoustic metasurface, we provide a complete and systematic procedure for theoretical analysis and design of the metasurface with a consideration of the visco-thermal effects in the medium. By fabricating the metasurfaces obtained from the design procedures via 3D printing technology, their absorption coefficients are experimentally measured in impedance tube, and compared to the state-of-the-art absorbers. Furthermore, we propose a new type of hybrid resonators with multiple micro-perforations and embedded necks to realize further broadband absorption of low-frequency sounds.