摘要：弹性超材料可被用于实现多种特殊功能,例如振动控制和波操纵,其中吸声是声学超材料完成的典型任务.利用机器学习方法反向设计超材料因利用数据驱动且不依赖经验的优势而备受关注,成为重要的设计范式之一.但现有的工作大多集中在验证反向设计神经网络的设计准确性,很少有人探索如何利用神经网络进行反向设计以提高材料性能.为此,我们的工作研究了反向设计框架在提升3D多尺度空腔型声学超材料的声学性能方面的能力.框架中有正向和反向网络,在训练过程中将目标吸声曲线(100~10000 Hz)作为反向网络的输入,并输出具有满足此吸声曲线的相应超材料结构,随后将其输入正向网络进行声学性能评估.结果表明,经过训练的前向网络可对超过训练集结构参数范围的结构(既“未见过”的结构)进行高精度性能预测,因此具有较高泛化性能.更重要的是,反向网络能够自发地采用超出范围限制的结构参数,以确保满足平均吸声系数高于训练集中任何数据的吸声目标,因此可利用反向设计突破训练集中数据的声学性能,进行性能优化.通过超限探索,反向设计精度从仅有9.2%的设计拥有<0.0001的均方误差显着提高到99.6%.最后,利用案例证明神经网络拥有的超限探索能力对旨在提高性能的反向设计有重要意义.希望这项工作能为更高性能弹性超材料的优化设计提供支撑.

摘要：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 l0 kHz for normal incidence, and the influence of the incident angle is also discussed.

摘要：Acoustic cloak based on coordinate transformation is of great topical interest and has promise in potential appli- cations such as sound transparency and insulation. The frequency response of acoustic cloaks with a quantity of discrete homogeneous layers is analyzed by the acoustic scattering theory. The effect of coordinate transforma- tion function on the acoustic total scattering cross section is discussed to achieve low scattering with only a few layers of anisotropic metamaterials. Also, the physics of acoustic wave interaction with the interfaces between the discrete layers inside the cloak shell is discussed. These results provide a better way of designing a multilayered acoustic cloak with fewer layers.