TABLE OF CONTENTS Lee et al. [103] fabricated a micromachined flow sensor using the periodic flapping motion of a planar jet impinging on a V-shaped plate. The sensor detects the oscillating frequency of the periodically flapping jet either optically with the help of a colored fluid inserted into the middle of the flow stream or by a pair of resistors in front of the V-shaped plate, which has opening angles between 70 and 110 . The resistors were connected within a Wheatstone bridge and the output voltage was measured by an ADC. A schematic drawing of the micro flow sensor with a convergent nozzle and a V-shaped plate downstream is shown in Figure 9.35(a). Experimental data shows that the flow velocity is linear proportional to the frequency of the jet flapping motion. The flapping frequency for flow velocities of up to 4 mm/s was below 0.2 Hz with water as the test fluid [Figure 9.35(b)].
As an explanation for the flapping motion, Lee et al. [103] say that a larger pressure field may be developed with the presence of the V-shaped plate, and therefore, the impinging jet column interacts with the pressure wave...
