基于谐振结构的声学超界面对声波反常调控研究

Analogous to the unique control effect research of electromagnetic (EM) waves by EM metasurface, the unique control research for acoustic waves by the artificial designed acoustic metasurface (AMS) has become a hotspot in acoustic research field in recent 2 years. This project's main purpose is to design AMS by the resonant structure of split hollow sphere (SHS) presented before. Firstly, based on the acoustic resonant model theory and total waves analysis of finite element method, we systematically study the reflected amplitude, phase and energy distribution of the unit cell of SHS and its evolutionary structure with different geometry parameters which contained split hole's diameter, the number of the holes, the sphere's diameter, and so on. From the resluts, we retrieve the relationship between the resonant units' geometry parameters and reflected phase in the low reflected loss case. Sencondly, we find the appropriate unit cells with a large phase converge of 0-2π to build some reflectarrays according to the defined arrangement mode, which can be used to design AMS with unique effects. The simulation is conducted to research the acoustic metasurface's anomalous reflection, plate focusing at the audible frequency band or the untrasound band in the free space of air or water environment. At last, we will fabricate the AMS sample by machining process and experimentally test the sound field ditribution in the free space of air and water environment to confirm the unique physics effects. From the simulation and experiment, we can further understand the physical machanism of the anomalous control for acoustic waves by the AMS. This project will explore the regularity of the AMS' anomalous control behavior for the acoustic waves and pave the way to the development and application of the AMS.

类比于电磁超界面对电磁波的反常调控效应，人工设计的声学超界面对声波的反常调控成为近两年来声学领域的研究热点。本项目主要是基于前期提出的开口空心球共振结构设计声学超界面。首先以声学共振模型理论和有限元仿真的全波分析方法为基础，系统研究开口孔径、开口数目、球直径等几何参数对开口空心球及其演化结构单元的反射幅值、相位、能量场分布等性能和指标的影响，揭示不同结构单元在低反射损耗条件下相位随几何参数的变化规律；然后提取具有0-2π相位分布的结构单元，通过一定的空间排列方式构建反射阵列，并利用反射阵列仿真设计声学超界面,研究其在空气和水介质中对可听声和超声频段声波的反常反射、平板聚焦成像等效应；最后加工制备出声学超界面样品，经由实验测试的反射声场分布验证这些奇异物理效应。进而加深理解声学超界面对声波反常调控的物理本质，探索出声学超界面调控声波传播行为的变化规律，为声学超界面的发展和应用提供基础。

人工设计的超界面材料具有超薄、损耗小、低造价、高度集成性等优点，利用超界面实现对声波的反常调控是近几年研究热点。本项目主要是基于前期提出的单开口空心球和双开口空心球共振结构设计和制备声学超界面。首先以声学共振模型理论和有限元仿真的全波分析方法为基础，系统研究开口孔径、开口数目、球直径等几何参数对开口空心球及其演化结构单元的反射幅值、相位、能量场分布等性能和指标的影响，揭示不同结构单元在低反射损耗条件下相位随几何参数的变化规律；然后提取具有0-2π相位分布的结构单元（单开口空心球单元10个，相邻单元之间的相位差为π/5；双开口空心球单元8个，相邻单元之间的相位差为π/4），通过一定的空间排列方式构建反射阵列，并利用反射阵列仿真设计声学超界面，基于有限元的仿真超界面可以实现反常反射，即当声波垂直入射时，反射波的角度满足广义Snell定律公式，两种单元设计的超界面分别在1100 Hz和1700 Hz具有反常反射效应。超界面的反常反射效应并不是在单一的谐振频率，而是在谐振频率附近具有一定的频带宽度，且反射角度随着梯度相位的改变而变化，实验中搭建了一台声学波导管测试装置，利用声脉冲法可以将入射信号和反射信号分开，从而测试出反射声场，实验测试结果表明垂直入射的声波在4000 Hz发生斜反射，且反射波前与仿真结果一致。同时，当声波斜入射，通过设计合适的梯度相位，可以实现负反射现象，即入射波和反射波在法线同侧。最后，利用双开口空心球设计合适的相位，使得入射的平面波波前转化为会聚的球面波波前，从而实现平板聚焦的超棱镜；也可以将平面波波前转化为锥面方式会聚，从而实现平板锥面聚焦成像效应的锥棱镜；最后加工制备出声学超棱镜样品，实验测试在焦点处声压出现极大值。通过对声学超界面的仿真计算和实验验证，加深了对声学超界面对声波反常调控的物理本质的理解，即通过相位调控波前的机理。进而探索出声学超界面调控声波传播行为的变化规律，为声学超界面的发展和应用提供基础。