Temperature influence on a differential capacitive rain sensor performances

The temperature influence on the performances of a differential capacitive rain sensor for windows was numerically investigated by Finite Element Method (FEM) before experimental validation. The sensor consists of three coplanar electrodes deposited on a glass substrate defining two capacitors: sensing and reference capacitor. Two types of window glass were used: ordinary and laminated. Despite a significant temperature influence on the capacitances, it turned out that, for sensors made with ordinary glass, the differential mode allows to offset the capacitances variations due to temperature fluctuations and to preserve the effectiveness of the sensor whatever the temperature in the range [−40 °C, +60 °C]. However, in the case of laminated glasses, simulations showed that the differential operating mode was insufficient to completely wipe out the temperature influence on sensor performances because of different temperature dependences of the materials permittivities. In this case, increasing the sensor operating frequency (1 kHz to 100 kHz) resulted in an improved balance of the sensor capacitances while the sensor effectiveness remained preserved.