Development of a Miniature Shear Sensor for Direct Comparison of Skin-Friction Drags

This paper presents the design, fabrication, and characterization of a silicon-micromachined mechanical sensor that directly compares the wall shears of two different surfaces in a liquid flow. The 27 mm × 27 mm sensor contains two 10 mm × 20 mm × 0.2 mm plates suspended to displace in proportion to the shear force on each surface. The monolithic sensor designed to compare skin-friction drag on two different surfaces consists of two floating plates, each suspended from a frame by identical flexure beams etched out of a 0.2-mm-thick silicon wafer. Design of the sensor is assisted by finite-element analysis to ensure adequate structural characteristics in the intended flows and validated by experimental characterization. The fabrication process is presented in detail, including how to form millimeter-long beams with a uniform cross section in micrometers and release the centimeter-scale plates suspended by the delicate beams. This paper provides a guidance to develop a miniature shear comparator using silicon microfabrication technologies.