Noncontact displacement sensing with high bandwidth and subnanometer resolution based on squeeze film damping effect

Noncontact displacement measurement with high bandwidth and subnanometer resolution is critical for precision engineering applications. However, the existing displacement sensors with subnanometer resolution either require a special plate to be fixed on the object to be measured or are bulky and inconvenient to integrate with other instruments. The air film height between two plates affects the squeeze film damping coefficient, which has the potential for subnanometer displacement sensing. However, lacking comprehensive analysis, modelling and experimental research, the possibility of the use of the squeeze film damping effect for displacement sensing is still unknown. In this paper, the displacement sensing mechanism based on the squeeze film damping effect is thoroughly analyzed, and the related experiments are conducted. The air film height is converted into the vibration amplitude of a resonant microcantilever. Then, the cantilever vibration amplitude is measured by the optical lever method, and finally, the noncontact sample displacement measurement is realized. The squeeze film damping force on the plate is analyzed, and the model of the vibrated cantilever subject to squeeze film damping force is established. It is found that increasing the driving amplitude can improve the sensitivity of the displacement sensing and reduce the measurement noise. Experimental results show that the resolution of the surface displacement measurement is 0.5nm, the linear region is about 8μm, and the measurement bandwidth of the sensor is 700Hz.