US Patent 7222531 Capacitive humidity sensor

A capacitive humidity sensor for detecting a humidity change includes a first sensor element having a first capacitance, a second sensor element having a second capacitance and connected in series with the first sensor element, and a humidity sensitive layer having a dielectric constant, which changes in accordance with humidity. The first and the second capacitances change with respect to the humidity change at a different rate. The humidity is detected using the different capacitances of the first and the second sensor elements. The humidity sensitive layer is formed to each sensor element so that each sensor element can be effectively protected.