固体双负介质超分辨率声波聚焦研究

Solid double-negative (DNG) mediums can focus acoustic wave beyond the diffraction limit, and can be used to realize acoustic super-resolution imaging. However, the progress of super-resolution imaging techniques are being slowed down due to some fundamental problems, such as the absence of dynamic homogenization model of predicting evanescent wave behaviors of solid DNG mediums and less understanding of their wave characteristics in the time domain. As the goal of this research project, acoustic super-resolution imaging by solid DNG mediums will be investigated. By studying the dynamic homogenization method, wave characteristics in the time domain, as well as the fabrication and experiment methods of solid DNG mediums. We will establish the design theory of acoustic superlens made of solid DNG mediums. To this end, the analytic model of solid DNG mediums will be built by using multiple scattering theory at first. On the basis of the analytic model, the dynamic homogenization method of predicting evanescent wave behaviors will be studied. Then, by use of Finite-Difference-Time-Domain (FDTD) computational method, study the time-domain characteristics of acoustic focusing field by solid DNG mediums. Analyze the relation between the intensity of surface states and the spatial resolution of the focused spot in the case of the excitation of the finite-period wave signals. Finally, the design, fabrication, and experiment testing of low-loss solid DNG mediums will be conducted.

固体双负介质具有高分辨聚焦特性，可以用于声波超分辨率成像，但目前还存在一些关键性问题亟待解决，如缺乏预测凋落波响应的动态均匀化模型及对于聚焦声场的时域响应特征不清楚等问题，阻碍了声波超分辨率成像的实现。为此，项目以固体双负介质实现声波超分辨率成像为研究目标，通过研究固体双负介质的动态等效方法、时域响应特征及制备和实验方法，系统给出固体双负介质声波超透镜的设计理论。为此，将首先利用多重散射理论建立描述双负介质结构动态响应的解析模型，从中研究预测凋落波响应的动态均匀化方法；然后利用时域有限差分数值计算方法，研究固体双负介质形成超聚焦声场的时域特征，分析有限周期波动载荷下表面波的激发强度和聚焦分辨率的关系；最后进行低损耗固体声波超透镜的设计、制备和功能测试。

项目系统开展了固体超材料声波超分辨成像与声波调控的物理机理、微结构设计和实验研究。取得的主要研究成果有：设计出固体双负介质多级结构构型，数值验证了声波超分辨聚焦效应；发展了计算Drude和Lorentz频散超材料时域波动响应的时域有限差分方法，揭示了超分辨聚焦声场的时域演化特征；设计出软质声波双曲放大超材料，实验验证其超分辨成像效应具有抵抗结构变形的能力；提出了宽频各向异性密度声波超材料，数值验证了该类超材料的水声调控功能，上述研究成果在医学成像、无损检测、水声调控等领域具有潜在的应用价值。基于上述研究进展，在著名声学期刊Journal of the Acoustical Society of America和著名物理期刊Applied Physics Letters等发表SCI收录期刊论文10篇。项目负责人获得国家优秀青年科学基金，培养1名研究生获得北京理工大学优秀硕士论文，作为联合主席在国内外学术会议组织超材料专题研讨会7次。