光热激励下微悬臂梁在流体中的振动研究

微悬臂梁结构广泛应用于微纳电子机械系统. 在实际应用中，涂层和工作环境的变化对微悬臂梁结构动态工作模式有着不容忽视的影响. 运用流体中双层微悬臂梁的光热振动模型，研究了在激光光热驱动下，金涂层微悬臂梁在不同流体中的振动特性. 理论上得到了微悬臂梁的温度场，光热驱动力和振动变形场的解析表达式. 研究结果表明，流体环境对微悬臂梁的光热振动谱有显著的影响，主要表现在共振频率的偏移和品质因子的变化两个方面. 相比较于悬臂梁在真空中的响应，当悬臂梁在空气中振动时，共振频率向低频产生微小的漂移（0.7%），共振峰未发生明显变化；然而，当悬臂梁在液体中振动的时候，共振频率向低频产生巨大的漂移（58%~80%），而且品质因子发生量级上的减小，共振峰发生了畸变. 本研究对微纳探测以及原子力显微镜等仪器的设计优化，有着一定的理论指导意义. 

STUDY ON THE VIBRATION OF MICROCANTILEVERS IMMERSED IN FLUIDS UNDER PHOTOTHERMAL EXCITATION

Microcantilever-based structures can be widely applied in Micro-Electro-Mechanical System and Nano-Electro-Mechanical System (MEMS and NEMS). In the practical application, the dynamical response of the cantilever strongly depends on the properties of coating film and surrounding medium. Based on the photothermal vibration model of bilayer microcantilever immersed in fluids, the dynamical responses of coating microcantilever were analyzed. The expressions for temperature, photothermal driving force and dynamical deflection fields were obtained analytically and showed graphically. Theoretical analysis showed that fluids, especially the liquids, have a significant influence on the vibration frequency spectra of microcantilever. Also it could be concluded that when the cantilever vibrated in air, the resonant frequency has a small shift (0.7%) to lower frequencies and resonant peak has almost no change compared to the response in vacuum. However, when the cantilever vibrated in liquids, the resonant frequencies have a distinct shifts (58～80%) to lower frequencies and resonant peaks are distorted, and quality factor decreased on the order of magnitude. This study can be of value to users and designers of microcantilever-based structures in micro-nano detections and AFMs.