ABSTRACT
Capacitance-type humidity sensors are a huge part of existing humidity sensor types, as they offer significant advantages in terms of simplicity of fabrication, sensitivity, and low-power operation. They dominate in atmospheric and process measurements and are the only types of full-range relative humidity (RH)-measuring devices capable of operating accurately down to 0% RH. According to estimations, capacitive RH sensors represent more than 75% of the available humidity sensors on the market. In this chapter, readers will find a description of the basic principles of operation and the electrode configurations used in such sensors, in particular parallel plate structures and planar capacitive sensors with interdigitated electrodes. The requirements for humidity-sensitive materials suitable for use in capacitive humidity sensors are also analyzed in this chapter. Much attention is also paid to describing examples of capacitance-based humidity sensors developed using different approaches.
