Measuring in the Subnanometer Range: Capacitive and Eddy Current Nanodisplacement Sensors

In this article, an overview of capacitive and eddy current sensors (ECSs) for measuring very small displacements in the subnanometer range is presented in view of the latest advancements in the field. The need for an accurate displacement/position measurement in such extremely small scales as nanometers and picometers has increased significantly during the last few years. Application examples can be found in high-tech industry, metrology, and space equipment manufacturing. A better understanding of the commonalities between these two types of sensors, as well as the main performance differences and limitations, will help to make the best choice for a specific application. The comparative survey in this article is based on both theoretical analysis and experimental results. The main performance criteria used are sensitivity, resolution, compactness, long-term stability, thermal drift, and power efficiency.