A MEMS device for measurement of skin friction with capacitive sensing

A microfabricated floating-element sensor for the measurement of wall shear stress is developed. The design objective is to measure shear stress in the range of 0.1 to 2 Pa, with a spatial resolution of O(100 μm). The sensor is micromachined in an ultra-thin silicon wafer using wafer bonding and DRIE techniques. Preliminary test results have been obtained by applying an electrostatic force to the sensor instead of a fluid force. The floating element deflection is then measured using direct and differential capacitance techniques as well as an optical method for additional confirmation of the results. These test results have been compared to theoretical simulations using MEMCAD software. The results show that with this sensor design it is possible to measure a shear force as small as 5 nN ± 0.5 nN, corresponding to a shear stress level of 0.05 Pa ± 0.005 Pa