声波在电流变液调控的超表面中传播行为研究

Metasurface is one of the hottest research topics in acoustics over the past few years. Metasurfaces exhibited phase discontinuity could be used to modulate plane wave propagation. Previous research have demonstrated that acoustic meta-atom structures consisting of split hollow spheres (SHS) and hollow tubes (HT) is capable of realizing acoustic metamaterials (AM) with single negative modulus or single negative mass density. A “flute-like” meta-molecule structure comprised of perforated hollow tubes (PHT) could be used to fabricate double-negative AMs at high or low acoustic frequencies.This proposal is based on the idea that acoustic meta-atom and meta-molecule structures might be engineered to exhibit behaviors of acoustic metasurfaces (AMSs) leveraging their phase discontinuity property.We will construct a physics-based model and develop a computational method for the AMSs which consist of acoustic meta-atom and meta-molecule structures. We will systematically investigate the interactions between AMSs and air, water or soft materials (e.g.electrorheological fluids) in order to develop a simple and cost-effective fabrication technique for this tunable and broadband engineered material. Proper design of the phase gradient of AMSs filled with soft materials could produce tunable wavefronts modulation including anomalous reflection and refraction. Many attractive properties of AMSs (e.g.super-thin, low loss, low manufacturing cost, and ease of being integrated, etc.) would make it possible to design fully tunable acoustic devices. For instance, one of the promising applications of proposed technology is to develop future ultrasonic diagnostic instruments with significantly higher resolution.

界面相位不连续的波传播理论模型已经吸引了研究者很大的关注. 基于文献分析和我们这几年关于声学超原子、超分子材料研究的基础，本申请提出建立声学超原子、超分子的超表面材料物理模型和计算方法；系统研究空气、水和电流变液等软物质介质与声学超表面材料耦合行为等物理效应，建立局域共振激元与空间相位、反射幅值、能量场的色散关系；发展简单、低廉制备智能可调谐基体声学超表面材料设计制备技术；通过调节空间的梯度相位设计声学超表面材料，实现智能调控声波的反常反射、平板聚焦成像等效应；探索声波在软物质调控超表面材料中的传播变化规律。超表面材料的超薄、低损耗、低造价、高度集成性等优点,有望制备可控的声学器件，实现对声波的任意调控功能，具有很大的发展空间。本项目研究结果可以为基于声学超表面材料的医学高分辨率的超声成像等新一代器件设计提供基础。

基于超分子单元构筑声学超材料基础，提出了一种深亚波长厚度声学反射型超表面模型，由超原子、超分子、簇以及簇集依次组成，调节两种超原子结构参数可以实现对反射声波的相位调控，使超分子单元实现0到2π反射相位变化。仿真和实验验证了这种厚度只有波长1/16的超薄型超表面。提出一种亚波长尺寸超分子单元宽频高效完美吸声吸收体，利用超分子与多孔材料耦合提升“吸声谷”的特性，数值模拟与实验结果表明该吸收体可以实现宽频（1800 -5300 Hz）高效（90%以上）吸声。设计了泡沫金属和淀粉硅油基电流变液超材料结构，实验结果表明这种超材料结构对水中35—80 kHz超宽频带超声波的透射波幅值和相位具有调控作用，电流变液流变特性产生的微结构与多孔泡沫金属相互作用影响了声波的传播。利用双开口空心球设计和制备了一种亚波长厚度透射型负折射超表面，实现透射相位覆盖2π的变化，制备的锥形聚焦平板透镜，强度可达入射强度的3.78倍。提出亚波长尺度声学拓扑绝缘体，利用局域共振思想设计不同于布拉格散射受拓扑保护的传播方式。实现狄拉克锥可调，打开狄拉克点形成平庸和非平庸带隙，模拟和实验验证了边界传输效应。由声学超分子设计了平移和镜面对称性破缺拓扑绝缘体超材料，实现拓扑相变类比量子自旋霍尔效应机制，模拟和实验实现受拓扑保护的稳健边界传输。提出红光、黄光和绿光波段一阶微分银树枝超表面，仿真得到反射系数分布与理论预测基本吻合。制备的银树枝超表面样品在绿光和红光波段测试的超表面反射率曲线与仿真和理论预测基本一致。设计了反射式银树枝状结构超表面模型，在可见光波段证明其积分运算性质。提出准周期树枝超表面，仿真和实验表明，准周期超表面具有和周期超表面几乎相同的光学响应行为，这种准周期超表面通过简单的电化学沉积法即可大面积制备。测试的准周期树枝超表面表明反常光自旋霍尔效应。这些新型声学和光学超表面为声波波前调控与全光信息处理系统提供了新方法，具有广阔发展前景。