Laminated plate-type acoustic metamaterials with Willis coupling effects for broadband low-frequency sound insulation

Acoustic metamaterials provide a powerful tool for designing effective noise-reducing means at subwavelength scales. This paper is concerned with the sound insulation characteristics of plate-type acoustic metamaterials under some pragmatic conditions, including the effect of structure scale on the sound insulation performance, the Willis coupling effect in multilayer plate-type acoustic metamaterials, and the acoustic coupling between plate-type acoustic metamaterials and existing structures. Herein, laminated plate-type acoustic metamaterials (LPAM) composed of multilayer plate-type acoustic metamaterials sandwiched with porous materials are constructed to effectively insulate broadband low-frequency noise. By a numerical study on the normal, oblique, and diffuse-field incident sound transmission loss (STL) of the proposed LPAM and its constituent layers, the presence of superior sound insulation performance and the governing physical mechanism are discussed. The effectiveness of numerical study is validated by the STL experiments performed in a sound impedance tube for small-scale samples and in a reverberation and anechoic chamber for large-scale samples. The proposed LPAM construction, analysis technique, and reported findings may contribute to the design and application of plate-type acoustic metamaterials for broadband low-frequency noise control.