A NEW SILICON GAS-FLOW SENSOR-BASED ON LIFT FORCE

This paper presents the first silicon-flow sensor based on lift force. The sensor is a bulk-micromachined airfoil structure that uses the li ft force as a sensing principle. The lift force acts normal to the flo w in contrast to drag-force sensor types, where the force acts in the how direction, The sensor utilizes the special distribution of the lif t force along the length of the sensor structure, Since the sensor, li ke an airfoil, is mounted at a small angle to the flow, it induces ver y little flow disturbance. The sensor consists of two plates connected to a center beam. Each plate is 5 x 5-mm square with a thickness of 3 0 mu m The flow-induced forces deflect the two plates in the same dire ction, but with different magnitude. The deflections are detected by p olysilicon strain gauges. The differential mode bridge makes the senso r insensitive to common mode deflection, e.g.,:acceleration forces. Th e lift-force principle is characterized using fundamental airfoil theo ry. The sensor has been experimentally verified, and a flow sensitivit y of 7.4 mu V/V/(m/s)(2) has been measured in both flow directions.