Composite sub-wavelength acoustic metasurfaces for acoustic mode attenuation

• Published in: International journal of mechanical sciences 2024-08, Vol.276, p.109363, Article 109363
• Main Authors: Yuan, Tianyue, Han, Jun, Xu, Xiaoxiao, Zhou, Jie, Bu, Huanxian
• Format: Article
• Language: English
• Subjects: Composite acoustic metasurface; Duct mode attenuation; Embedded walls; Porous materials; Sub-wavelength
• ISSN: 0020-7403
• DOI: 10.1016/j.ijmecsci.2024.109363

This paper reports an experimental investigation of a phase-gradient acoustic metasurface for duct acoustic applications, to evaluate the potential for attenuating acoustic modes and to understand the associated mechanism. The metasurface is a composite configuration where melamine foam as the main part includes a tunable wall. Given a target sound-absorbing frequency, a deeply sub-wavelength metasurface with a thickness-to-wavelength ratio of 1/6.86 is achieved. The unique way of assembling annular metasurfaces offers the possibility of fabricating three different configurations, which are then tested in a duct acoustic rig with artificially generated modes. The performance is assessed through in-duct modal analysis and far-field measurements. The results indicate excellent mode attenuation performance of the designed metasurface at broadband frequencies. The numerical simulation suggests that the mechanism can be related to the conversion from the incident mode to the evanescent waves due to the metasurface. In addition, the effects of the mode suppression are enhanced with the increase of the mode order, which can be attributed to the fact that the performance of the metasurface is influenced by the modal incidence angle. Overall, the present work provides a fascinating noise control method for ducted propulsion systems, and aeroengines in particular. [Display omitted] •Designs of a deeply sub-wavelength metasurface with a thickness-to-wavelength ratio of 1/14.3 is achieved for duct acoustic applications.•A process of fabricating an annular metasurface is demonstrated.•The mode attenuation performance of the metasurface is evaluated under the incidence of controllable acoustic modes at broadband frequencies.•The sound absorption mechanism of the metasurface is revealed through simulations.