Measurement of flow direction and velocity using a micromachined flow sensor

A circular-type thermal flow sensor was designed and fabricated using MEMS technology in order to detect flow direction and velocity, simultaneously. The designed sensor needs only one heater to operate the flow sensor, so the detection of flow direction and velocity can be accomplished in small dimension and low power consumption. A silicon diaphragm was formed on the back of the sensors to minimize the heat conduction effect and heat capacity. Furthermore, a gap between a heater and four detectors was formed to optimize heat transfer. In order to evaluate the gap effect, a differently structured sensor was designed and fabricated, and their properties were compared. From the tests results of the two designs, the sensitivity of the sensor, which has a gap, is two times more sensitive than the other sensor, which has no gap. Therefore, it can be concluded that the gap between a heater and four detectors is effective for reducing conduction effect. The test results of the designed sensor show the maximum angle difference was 5degrees and the velocity error was no more than 0.5 m/s. Power consumption was 80 mW and the response time was only a few seconds. (C) 2004 Elsevier B.V. All rights reserved.