Four-wire orthogonal structure for accurate measurement of fluid velocity and wind flow direction using silicon micro-machining on silicon nitride membranes

Microelectromechanical thermal sensors are one of the most accurate and important tools for measuring the direction and velocity of an acoustic wave and winds. Detection of wind direction and speed in different ranges has different applications such as meteorology, wind power plants, gas flow measurement in smart building and gas consumption of power plants. In this paper, a four wires sensor is designed and built to measure the velocity and direction of a fluid simultaneously. Comsol Multi-physics software has been used for simulation and design. To increase the sensitivity of the sensor, the all of sensor elements are fabricated on a silicon membrane to reduce the heat transfer of the structure with the sensor body. To detect the direction, a four-wire and orthogonal structure has been used, which provides the ability to measure the direction up to 5 degrees. A test set-up was designed and built to characterize this sensor, and the sensor was tested up to speeds of 5 meters per second, which is the range of industrial flow-meters, wind and gasometer of smart building. By changing the distance of the wires, this sensor is able to measure speeds of 30m/s.