Design of a micro floating element shear stress sensor

A silicon-based micro-machined, floating element sensor for wall shear-stress measurement has been developed. Sensor with the dimension of 4×3×0.5mm³ has been fabricated by inductively coupled plasma (ICP) etching techniques with single mask. An optical system was designed to identify whether there is defect in the structure of the fabricated sensor. Detection of the floating element motion induced by shear stress of fluid is accomplished using differential capacitance measurement. A special package was used to reduce the parasitic capacitance and realize flush mounted between the sensor and the wall. Calibration tests were carried out in a laminar flow channel; the result indicates that the sensitivity of the sensor is measured to be 27mv/Pa. The measured non-linearity is less than 3.4% while the repeatability is within 4.9% in the regime of 0-35Pa.