A thin film micro-force sensor using double concentric circle optical fibre

Abstract

For the purpose of measuring µN- and mN-level micro-force, the optical reflection characteristics of a circular thin film are utilized to develop a micro-force sensor and double concentric circle fibres are used to measure the micro-force. This paper focuses on the relation between the output parameters of the system, namely the voltage ratio of the two receiving fibres, and the micro-force, the diameter, the thickness and the materials of the thin film, as well as the displacement between the fibre probe and the film. A measurement platform has been set-up and a large number of experiments have been conducted to determine the relationship between the voltage ratio and the micro-force, the diameter and the thickness of the thin film by using a least square exponential fitting algorithm. Furthermore, the errors between the calculating values from the fitting equation and the experimental values are obtained and analysed, which supports the conclusion that when the micro-force is in the range of 0–10 mN, the equation can be used to measure the micro-force with the resolution of 10 µN in the error range of −1.5%–+2.5%, and an automatic measurement process is realized.