Cordwood space-coiling metasurface and its frequency band control method for noise reduction

Following the principles of acoustics, designing building blocks with different functions and constructing acoustic metasurfaces through block splicing is of practical importance in engineering due to its advantages of quick installation, wide application, and reusability. In this paper, based on generalized Snell’s law, two kinds of space-coiling block configurations are proposed for phase control and refraction control functions, respectively. The acoustic modulation effects of the blocks are analyzed and the calculation method of their bandgap characteristics is given. On this basis, cordwood space-coiling metasurface and its frequency band control method for noise reduction are presented, via constructing a metasurface by assembling multiple building blocks, and achieving the noise reduction requirement based on the noise cancellation mechanism and bandgap characteristics. According to the presented method, two types of building blocks are designed and produced in accordance with the defined noise reduction objectives. Through splicing different types and numbers of building blocks, two space-coiling metasurfaces are assembled in order to, respectively, satisfy the noise reduction requirements in different frequency bands. The acoustic experimental research in the fully anechoic laboratory confirmed the noise reduction effect of both metasurfaces in their respective working frequency bands. Both of them deliver significantly better-than-expected performance in the key frequency bands. It is shown that the cordwood acoustic metasurfaces can meet the noise reduction requirements of different frequency bands by means of the convenient and fast block splicing. Indicated that the cordwood space-coiling metasurface and its frequency band control method can be effectively used for noise reduction.