A novel micromachined flow sensor using periodic flapping motion of a planar jet impinging on a V-shaped plate

Abstract

Here we present a novel micromachined flow sensor capable of detecting small amounts of volumetric flow rates (down to 2 nl/s) and extra-low flow velocities (down to 0.15 mm/s). The innovative flow sensor detects a periodic flapping motion of a planar jet impinging on a V-shaped plate downstream. Instead of sensing DC current or voltage signals induced by small volumes of the flow, the microflow sensor detects the oscillating frequency of the periodic flapping jet, resulting in a higher sensitivity and a larger dynamic range than that of the existing products. The microflow sensor is fabricated on a quartz substrate using wet chemical etching and metal masks. It is composed of a planar convergent nozzle, a V-shaped plate downstream and a pair of sensing resistors. The microflow sensor is characterized both optically and electrically. First, a dye-containing sample flow is used to visualize the flapping motion of the impinging jet under a microscope. Flapping motion is confirmed experimentally even at a low flow velocity (0.15 mm/s). Then, the flapping frequency is detected using built-in microsensing resistors driven by a constant-current circuit. Data from microscopic flow visualization and electrical sensing are highly consistent. It indicates that even in microscale the flow velocity is still linearly proportional to the frequency of the jet flapping motion. Therefore, the velocity or volumetric flow rate of small amounts of the flow can be measured by detecting the flapping frequency. Note that the test Reynolds number ranges from 0.2 to 5.4 in the present study. It is the first time that low-Reynolds-number flow is reported with a flapping motion for flow impinging on a V-shaped plate. The microflow sensor can be applied in various fields, including biomedical detection, micrototal analysis system, smart fluidics etc.