Mechanism for the behavior of hydroactive materials used in humidity sensors

The theory of operation of humidity sensors has not been widely discussed in the literature. In particular, no convincing explanation has been given as to why they respond to relative humidity (RH) rather than to an absolute measure of humidity, such as vapor pressure or mixing ratio, over a wide temperature range. A simple mechanism based on the adhesion of surface water to polarized solids is presented that explains many of the properties of these sensors.

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