Acoustic anechoic layers with singly periodic array of scatterers: Computational methods, absorption mechanisms, and optimal design

Abstract

The acoustic properties of anechoic layers with a singly periodic array of cylindrical scatterers are investigated. A method combined plane wave expansion and finite element analysis is extended for out-of-plane incidence. The reflection characteristics of the anechoic layers with cavities and locally resonant scatterers are discussed. The backing is a steel plate followed by an air half space. Under this approximate zero transmission backing condition, the reflection reduction is induced by the absorption enhancement. The absorption mechanism is explained by the scattering/absorption cross section of the isolated scatterer. Three types of resonant modes which can induce efficient absorption are revealed. Due to the fact that the frequencies of the resonant modes are related to the size of the scatterers, anechoic layers with scatterers of mixed size can broaden the absorption band. A genetic optimization algorithm is adopted to design the anechoic layer with scatterers of mixed size at a desired frequency band from 2 kHz to 10 kHz for normal incidence, and the influence of the incident angle is also discussed.

Grating‐like anechoic layer for broadband underwater sound absorption

“…Typically, viscoelastic material is a kind of material with both elasticity and viscosity. When viscosity is dominant, such as in petroleum, it is commonly characterized using the complex viscosity model $${\mu }_{{\rm{c}}}=\mu (1+j{\gamma }_{{\rm{s}}})$$, 53 while when elasticity is dominant, such as in rubber, it is usually characterized using the complex modulus model $${G}_{{\rm{c}}}=G(1+j{\eta }_{{\rm{s}}})$$, 54,55 where $${G}_{{\rm{c}}}$$ and $${\eta }_{{\rm{s}}}$$ are, respectively, the complex shear modulus and the loss factor, and $${\mu }_{{\rm{c}}}$$ and $${\gamma }_{{\rm{s}}}$$ are the complex viscosity and the elastic phase, respectively. With small deformation assumed, when rubber is subjected to the excitation of a harmonic wave, the solid constitutive model using complex modulus is completely equivalent to the fluid constituting using complex viscosity and $${G}_{{\rm{c}}}$$ and $${\mu }_{{\rm{c}}}$$ can be related by $$${\mu }_{{\rm{c}}}=-j\,\cdot \,\frac{{G}_{{\rm{c}}}}{\omega }.$$$…”

A review of underwater acoustic metamaterials

“…故频率越低, [61] . 考虑到含单一局域共振子的超材料 带隙宽度过窄, 可通过多层不同局域共振频率的超材 料叠加或采用单层具有多个尺寸(局域共振频率)的共 振子来拓宽低频水声吸声频带 [62,63] .…”

Topology optimization combined with a genetic algorithm to design structured materials for underwater broadband acoustic absorption

“…An acoustic resonator contains a viscoelastic material as its matrix with embedded scatterers such as cylindrical (Sven M and Ivansson, 2008; Zhao et al, 2018; Zhou et al, 2018), spherical (Sharma et al, 2020; Zhong, Zhao, Yang, Wang, et al, 2019), and variable section cavities and solid scatterers like steel plates (Yu et al, 2021; Zhang and Cheng, 2021; Zhong et al, 2021). Furthermore, the combination of rubber, internal cavities, and embedded steel plates might significantly improve broadband absorption performance (Jiang and Wang, 2012; Shi et al, 2019; Wang et al, 2021; Yang et al, 2014; Zhang and Cheng, 2021). Researchers have been able to obtain good acoustic structural materials by using size optimization methods (Liu et al, 2021).…”