Impedance model for a high-temperature ceramic humidity sensor

We present an equivalent circuit model for a titanium dioxide-based humidity sensor which enables discrimination of three separate contributions to the sensor impedance. The first contribution, the electronic conductance, consists of a temperature-dependent ohmic resistance. The second contribution...

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Bibliographic Details
Published in:Journal of sensors and sensor systems 2019-04, Vol.8 (1), p.161-169
Main Authors: Lensch, Henrik, Bastuck, Manuel, Baur, Tobias, Schütze, Andreas, Sauerwald, Tilman
Format: Article
Language:English
Subjects:
Capacitance
Electric properties
Electrodes
Engineering models
Equipment performance
Equivalent circuits
Frequency ranges
High temperature
Humidity
Humidity meters
Impedance
Relative humidity
Resistance
Sensors
Temperature dependence
Thermal properties
Titanium dioxide
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Summary:We present an equivalent circuit model for a titanium dioxide-based humidity sensor which enables discrimination of three separate contributions to the sensor impedance. The first contribution, the electronic conductance, consists of a temperature-dependent ohmic resistance. The second contribution arises from the ionic pathway, which forms depending on the relative humidity on the sensor surface. It is modeled by a constant-phase element (CPE) in parallel with an ohmic resistance. The third contribution is the capacitance of the double layer which forms at the blocking electrodes and is modeled by a second CPE in series to the first CPE. This model was fitted to experimental data between 1 mHz and 1 MHz recorded at different sensor temperatures (between room temperature and 320 ∘C) and different humidity levels. The electronic conductance becomes negligible at low sensor temperatures, whereas the double-layer capacitance becomes negligible at high sensor temperatures in the investigated frequency range. Both the contribution from the ionic pathway and from the double-layer capacitance strongly depend on the relative humidity and are, therefore, suitable sensor signals. The findings define the parameters for the development of a dedicated Fourier-based impedance spectroscope with much faster acquisition times, paving a way for impedance-based high-temperature humidity sensor systems.
ISSN:2194-878X
2194-8771
2194-878X
DOI:10.5194/jsss-8-161-2019