On the design of force sensors based on frustrated total internal reflection

Frustrated total internal reflection (FTIR) of light is a physical phenomenon which can be used to accomplish several measurement tasks. This paper deals with the design and modeling of pressure field or force sensors based on FTIR. In fact, it is possible to convert the value of contact pressure into a light intensity signal, owing to the frustration of reflection of a dedicated medium. In this sense, it is possible to measure pressure/forces with a camera system or a photosensitive sensor. In this paper, the physical principles of the technique are recalled. Then, an experiment will document the behavior of FTIR at micromechanical level. Consequently, a Greenwood-Williamson (GW) model is proposed as a tool to predict the response of the FTIR-based pressure sensor. Experimental data and uncertainty analysis show that the design methodology is able to predict the behavior of the sensor with an uncertainty that is about +/- 10% of the actual specimen response, thus providing an effective tool to optimize the FTIR experiments.