Effects of Ambient Humidity on a Micromachined Silicon Thermal Wind Sensor

The effect of ambient humidity on a micromachined silicon 2-D thermal wind sensor has been investigated. The sensor includes a central heater and four temperature sensors. It measures the flow-induced temperature gradient on the heated surface. Properties of the ambient air, such as density, viscosity, heat conductivity, and specific heat capacity, are theoretically presented to explore their effects on the performance of the sensor at different relative humidity levels. The output of the sensor as a function of wind speed at different relative humidity levels has been measured. It shows that there is a measurable effect at both high relative humidity and temperature. The results presented here provide a valuable reference for the practical applications of the wind sensor.