A ceramic humidity sensor using Ba0.5Sr0.5TiO3 doped with a few molar percent of potassium oxide was studied. It was characterized by long life, was reversible without repeated high-temperature thermal desorption processes, and conductance against relative humidity (RH) sensitivity, as high as four orders of magnitude, was found at low frequencies. This sensor showed a good exponential relationship between the conductance, RH, and temperature at low frequencies. The plots of the relative dielectric dispersion against RH showed that it had an apparent dielectric constant increase at low frequency as a result of the electrode and water molecular polarization effects. By complex impedance plots with a “non-Debye” capacitor concept, an equivalent circuit model was established which could well simulate all the electrical properties of the sensor in the range of 65—95 percent RH for all measured temperatures (25°C-85°C) and frequencies (5 Hz-13 MHz). In the measurement of this sensor, an inductance loop over the low RH (15 and 30 percent) and low frequencies (5 to 40 Hz) range was observed, which might be due to the desorption of water vapor at the electrode surface for reduction reactions.
|Number of pages||8|
|Journal||IEEE Transactions on Components, Hybrids, and Manufacturing Technology|
|State||Published - Jun 1989|