Development of MEMS airflow sensors

• Main Author: Abdul Rahman Mohd Hassan
• Other Authors: Miao Jianmin
• Format: Final Year Project
• Language: English
• Published: 2011
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics; DRNTU::Engineering::Electrical and electronic engineering::Microelectromechanical systems
• Online Access: http://hdl.handle.net/10356/44588
• Institution: Nanyang Technological University

This report documents the development of low-cost MEMS air-flow sensors for the purpose of sensing wind-speed magnitude and direction. The development is to facilitate the Singapore-MIT Alliance for Research and Technology (SMART) study of the heating effects in an urban canyon, within the tropical island state of Singapore. The sensors consist of an array of micro-heaters that are fabricated using microfabrication technologies and installed on a 40 mm diameter sphere. Resistive heating of the micro-heaters is carried out through an input of a constant current source to each micro-heater. The heat transfer, predominantly via convection, is caused by the moving air as it flows past the heated surface of the micro-heater. This results in a change of the micro-heater resistances and is measured through the concurrent change in voltage. Test results indicate an exponential decay of micro-heater resistance with different wind directions and intensities of between 1 – 10 m/s. Stable resistance readings are achieved within 45 seconds as measured through the thermal time constant. With a steady-state temperature of more than 150° C, the effect of solar radiation on the micro-heaters is found to be negligible. Attempts at ambient temperature sensing to compensate for the effect of ambient temperature result in a linear resistive distribution for temperatures between 22 - 36° C. Results are indicative that with proper calibration and development of a suitable algorithm, sensing wind in two dimensions together with temperature detection can be achieved.