The HUMI.sens® is based on a capacitive humidity sensor. This sensor consists of a hygroscopic polymer material in which the water vapor from the measurement gas is stored. This incorporation changes the dielectric properties of the polymer material. The polymer material is located between the electrodes of an electrical capacitor and thus also changes the capacitance of the capacitor. The capacity increases almost linearly with the humidity. An equilibrium is formed between the moisture in the measurement gas and the moisture in the polymer, which reversibly adapts to the changing moisture.
The humidity sensor is built up in a layer structure. The bottom layer forms the carrier. This is made of ceramic. A base electrode is applied to this carrier. The hygroscopic polymer layer is applied over this base electrode. A gas-permeable layer must be applied as a counter electrode so that the water vapor can get into this sensitive layer from outside.