Zhang Yanni, Pan Jie, Chen Kean, Zhong Jie
School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, People's Republic of China.
School of Engineering, the University of Western Australia, Perth, Western Australia, 6009, Australia.
J Acoust Soc Am. 2018 Aug;144(2):648. doi: 10.1121/1.5048797.
A structure for an underwater sound absorber with subwavelength thickness and a quasi-perfect absorption property at multiple frequency bands is reported. This absorber consists of a viscoelastic coating layer embedded with periodically distributed plate scatterers (PSs). The embedded PSs cannot only slow sound waves in the coating, leading to a down-shifted resonance frequency where the absorption is maximized, but also introduce multiple local bending modes and local longitudinal modes in the coating. Via proper selection of the parameters of the PSs and the PS array, multiple local resonance modes of different types in a coating unit can be excited, resulting in quasi-perfect absorption of incident sound at multiple frequencies whose wavelengths are much longer than the thickness of the coating layer. For example, absorption (89%) of underwater sound at 462.9 Hz is achieved by such a layer with a thickness of 6 cm, which is 1.9% of the wavelength of the incident sound. Broadband quasi-perfect absorption can also be realized by coupling of those multiple local resonant modes. This quasi-perfect absorption property can also be observed for sound waves with different incident angles, because a large number of local intrinsic modes could still be excited.
报道了一种具有亚波长厚度且在多个频段具有准完美吸收特性的水下吸声器结构。该吸声器由嵌入周期性分布的平板散射体（PSs）的粘弹性涂层组成。嵌入的PSs不仅能使涂层中的声波减速，导致吸收最大化的共振频率下移，还能在涂层中引入多个局部弯曲模式和局部纵向模式。通过适当选择PSs和PS阵列的参数，可以激发涂层单元中不同类型的多个局部共振模式，从而在多个频率下实现对入射声的准完美吸收，这些频率的波长比涂层厚度长得多。例如，这样一个厚度为6厘米的层在462.9赫兹时实现了水下声音89%的吸收，该厚度仅为入射声音波长的1.9%。通过这些多个局部共振模式的耦合也可以实现宽带准完美吸收。对于不同入射角的声波也能观察到这种准完美吸收特性，因为仍能激发大量的局部本征模式。
