新型电磁功能表面及其Casimir排斥力的电磁调控机理研究

The influence of Casimir force increases as the separation between two surfaces in Microelectromechanical Systems (MEMS) decreases, which limits the miniaturization of the MEMS due to the cause of adhesion failure. To solve this problem, we focus on the research of controllable Casimir repulsion by using a novel designed electromagnetic surface. The influence on Casimir force of materials with different electromagnetic response styles (Drude/Lorentz model etc.) as well as the contribution of electromagnetic parameters on different frequency ranges are discussed based on Lifshitz and scattering theory, according to which the new theory and methods to realize controllable Casimir repulsion are studied; Using the designing theory of meta-metamaterials in combination with the Extended Maxwell-Garnett theory (EMG), Extended Onsager's theory and Clausius-Mossotti theory (CM), we will explore the influence on effective electromagnetic parameters of the electromagnetic surface by the dimension, shape, electromagnetic parameters, filling fraction and spatial orientation of nano superparamagnetic particles, and explore the design and realization of new electromagnetic surface with a broadband and high frequency magnetic response satisfying Boyer's condition. We will discuss the variation in magnetization state of the constituent unit (superparamagnetic particles) of the electromagnetic surface with external magnetic field, in order to reveal the mechanism of the reversible transition between Casimir attraction and repulsion controlled by an external magnetic field. Finally, we will construct the MEMS friction pair by micro-nano processing in combination with self-assembly method and validate the realization of controllable Casimir repulsion. The research provides a new effective method to imporve the adhesion failure and active controll friction in MEMS.

微机电系统中由器件表面间距减小而导致的Casimir引力增大会引起器件粘着失效，限制其向更小尺度发展。本课题拟开展新型电磁功能表面及其Casimir斥力的电磁调控机理研究。由Lifshitz理论和散射矩阵理论出发，研究不同类型电磁响应色散介质对Casimir力的影响规律，探索新的Casimir斥力实现机理与方法；利用电磁超-超常介质（Meta-metamaterial）的设计理论，结合EMG理论和扩展Onsager理论等，研究超顺磁纳米颗粒的形状、大小、电磁参数和填充率等对电磁功能表面有效电磁参数的影响规律，探索满足Boyer条件的新型功能表面的设计与实现方法；研究电磁功能表面组成基元的磁化状态随外磁场的响应特性，揭示其外场调控Casimir引力与斥力转变的机理；采用微纳加工与自组装方法构建MEMS摩擦副，并验证其电磁调控特性。该研究为改善MEMS器件的粘着失效与摩擦主动控制提供了可能。

本项目按照计划执行，顺利完成研究计划。所取得的成果如下：（1）表面间Casimir引力与斥力的实现机理与理论计算方法研究：基于多层膜间Casimir力的理论计算方法，进行了多层膜结构模型的设计与数值计算，提出了一种通过多层膜结构参数的优化设计来调节MEMS中摩擦副间Casimir力的思路，并以此研究了金属和电介质材料膜层的影响、超-超常材料膜层的影响和外加场的影响。（2）基于超-超常介质理论的新型电磁功能表面设计与参数控制理论：基于超-超常介质的设计思想，利用非均匀的超顺磁纳米颗粒设计了一种人为构造的新型电磁功能表面，研究了颗粒尺寸的非均匀性等对电磁表面电磁参数的影响，以及对电磁表面Casimir力的影响，同时通过计算金球与电磁表面在各类液体中的Casimir力，发现Casimir斥力相比于自然材料显著增强，进一步发现Casimir斥力效应源于电磁表面的低介电特性。另外，基于表界面电磁微纳结构设计，理论提出并验证了长方体介质微纳结构实现各向异性电磁响应效应以及构筑特定各向异性的电磁参数的可行性。（3）外场调控Casimir斥力的实现机理、计算理论与数值仿真：基于Mie谐振介电超构材料实现液体介质中的Casimir稳态平衡及悬浮，并研究此稳态平衡及悬浮间距受介电超构材料构造参数和系统的几何参数的影响规律，给出介电超构材料的设计准则，并基于溶液浓度配比实现微球Casimir稳态悬浮。（4）新型电磁功能表面构建及其外场调控Casimir斥力的实验研究：利用原子力显微镜，进一步排除静电力，水动力和粗糙度等因素对测量实验的影响，精确测量了金-乙醇-金，金-乙醇-二氧化硅和金-环己烷-聚四氟乙烯三个体系中的Casimir力，其中首次测得金-环己烷-聚四氟乙烯体系当中的Casimir斥力。同时实验结果与利用不同介电模型得到的理论结果进行对比分析，研究了现有的液体介电模型的可靠性，并得到van Zwol等人提出的介电模型理论与实验结果的一致性最好。