LAUSR

SAW-based capacitance sensors were developed by measuring the changes in the voltage ratio between an output inter-digital transducer (IDT) and an input IDT, induced by the variation in the capacitance between hemi-spherical conductive tips with diameters on the order of micrometers. We derived the transfer and sensitivity functions, which describes the ratio of the variation in the output voltage to the variation in the input voltage with a 2-port network model of a SAW based on Mason’s equivalent electro-acoustic circuit and analytical model for the apex capacitance. We then conducted an experiment to verify and measure the transfer function and the 3-D shape. The system was found to have an average resolution of approximately 10 nanometers. We also used the constructed system to measure nano- and submicro-sized 3-D shapes, and verified that the measurement results were accurate.