Xu Fei, Guo Xinyi, Xu Linyan, Duan Xuexin, Zhang Hao, Pang Wei, Fu Xing
State Key Lab of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China.
Micromachines (Basel). 2017 Aug 7;8(8):244. doi: 10.3390/mi8080244.
The very small vibration of a solidly-mounted resonator (SMR) in fluid may trigger a relatively large motion of the covering fluid, which was implied by our protein-related experimental results. Therefore, a series of experimental methods for characterizing the mechanical longitudinal vibration of the SMR and the corresponding out-of-plane dynamic response of the fluid above the SMR surface is described in this paper. A SMR device with theoretical resonance frequency of 2.5 GHz was driven by an amplitude-modulated (AM) signal, in which the amplitude is modulated by a signal of the second resonance frequency of the atomic force microscope (AFM) cantilever. A lock-in amplifier is used to demodulate the vibration response of the AFM cantilever, which is proportional to the amplitude of the sample vibration in contact mode and tapping mode. The amplitude-frequency curve of the SMR surface is obtained in contact mode with a relatively stronger interaction force between the AFM tip and the SMR surface. The amplitude-frequency curve of the motion of the liquid above the SMR device and the peak amplitude of the fluid at different distances above the SMR surface are measured in tapping mode with a relatively weak interaction force between the AFM tip and the fluid sample.
牢固安装的谐振器（SMR）在流体中的微小振动可能会引发覆盖流体的相对较大运动，这在我们与蛋白质相关的实验结果中有所暗示。因此，本文描述了一系列用于表征SMR机械纵向振动以及SMR表面上方流体相应平面外动态响应的实验方法。一个理论共振频率为2.5 GHz的SMR装置由一个调幅（AM）信号驱动，其中振幅由原子力显微镜（AFM）悬臂的第二共振频率信号调制。一个锁相放大器用于解调AFM悬臂的振动响应，该响应在接触模式和轻敲模式下与样品振动的振幅成正比。在接触模式下，通过AFM针尖与SMR表面之间相对较强的相互作用力获得SMR表面的振幅-频率曲线。在轻敲模式下，通过AFM针尖与流体样品之间相对较弱的相互作用力，测量SMR装置上方液体运动的振幅-频率曲线以及SMR表面上方不同距离处流体的峰值振幅。
