微波频段表面WG模传感器的关键技术研究

WG mode (Whispering Gallery Mode) is a morphology-dependent resonance. At the the end of 19th century, the modern physical explanation of this effect was proposed by the British scientist Reyleigh based on his research on an ancient gallery located under the dome of St. Paul's Cathedral. After that, the research on whispering gallery modes has been gradually extended to the microwave and optical region, and its sensing application had attracted a great deal of attention. However, both the micro-ring, disk, or sphere dielectric resonators exhibit a common characteristic, that is, the mode field distribution is almost confined within the dielectric resonator. This becomes a bottleneck for further improving the sensitivity of dielectric resonator sensors. Recently, we found that a new kind of resonant mode, namely, the surface WG mode can be excited by covering a layer of metamaterials on the surface of a traditional dielectric resonator. Sensors based on surface WG mode possess much higher sensitivity than traditional dielectric resonator sensors since the evanescent field is greatly amplified. This project aims to investigate the characteristic and excitation mechanism of surface WG mode, with emphasis on the study of the correlations between the metamaterial structures and the material parameter distribution of the resonator. On this basis, a metamaterial based resonator will be designed and fabricated at microwave frequency band, and the surface WG mode resonance will be verified by experiment. Moreover, according to the requirement in the production process of Yunnan metallurgy industry, a prototype resonant sensor based on surface WG mode will be designed with the aim of mastering the key technologies. These studies may lay a solid foundation for the sensing application of surface WG mode.

WG模(Whispering Gallery Mode)是一种形态依赖的谐振模式，19世纪末，英国科学家Reyleigh基于对圣保罗大教堂回音廊的研究最早给出了WG模的理论解释。随后，WG模的研究被扩展到光波和微波频段，并迅速在传感器领域得到广泛应用。但无论是在圆环、圆盘或球形介质谐振器中，WG模的场分布主要集中在介质内部，渗透到外部的消逝场很少，这成为了进一步提高传感器灵敏度的瓶颈。最近，我们研究发现在介质谐振器表面覆盖超材料层能够形成一种新的谐振模式：表面WG模，并伴随着极强的消逝场放大效应，能够显著提高传感器灵敏度。本项目拟基于模式展开理论研究表面WG模的性质和产生机理，着重探讨超材料结构与谐振器材料参数分布的关联。在此基础上制备微波频段超材料谐振器，证实表面WG模效应，并针对云南冶金行业生产流程中的检测需求设计传感器原型，掌握其关键技术，为表面WG模的传感应用奠定理论和技术基础。

本项目研究了表面回音壁(Whispering Gallery: WG)模及传感应用，并在微波频段设计了传感器原型。详细如下：(1) 研究了多层介质圆环、圆盘的谐振特性和模式场分布，在负介电常数材料层覆盖下获得了表面WG模；模拟了在介质传感中，环境介电常数改变时，谐振频率的变化，结果表明，当相对介电常数变化0.01时，传感器相对频移为5.4THz，灵敏度为6.8µm/RIU。(2) 基于电感(L)和电容(C)网络设计了传输线超材料，建立了由LC网络构成的表面 WG 模谐振器模型，验证了表面WG模式，模拟了其传感效应，分析了电感、电容参数偏差等因素对模式分布的影响。(3) 研究了基于天然等离子材料金和石墨烯的介质微腔模式传输特性，产生了表面WG模式，并提出了基于物质分子与石墨烯表面传输模式相互作用形成耦合共振增强进行分子谱传感的方法。(4) 研究了褶皱金属周期结构的色散关系，并通过本征分析方法仿真了其传输模式，结果表明褶皱金属结构可以等效为负介电常数材料；褶皱深度增加时，模式传播常数增大，局域性增强，通过设计褶皱深度渐变的波导结构实现了传输波与消逝波的相互转换，以及分子谱传感；将褶皱金属周期结构弯曲形成环形获得了类似于表面WG模的谐振状态，并命名为类表面WG模，找到了在微波频段通过微带技术设计类表面WG模传感器的突破口。(5) 设计了由同心圆环形褶皱金属结构耦合构成的微波频段微带型类表面回音壁模式传感器模型；传感器由上下两层板构成，上层为蚀刻于介质基板上的同心圆环形褶皱金属结构，下层为微带传输线；两同心褶皱圆环之间耦合距离为调整传感器的工作频率增加了一个自由度。在对模型进行仿真和优化的基础上制备了传感器原型，建立了测量系统. 由于电场集中于两个耦合褶皱环形结构之间的间隔内，因此该区域对物质介电常数的变化非常敏感。通过实验验证了传感性能，结果表明该传感器不仅能够测量溶液浓度和分辨不同的溶液，而且能够测量纸片厚度，具有较好的线性度。