# Mitigating Electrochemical Effects in Resistive Frost-Detection Sensors
### Working Principles of a Resistive Frost-Detection Sensor
This effect impacts the electrical resistance measurements, making the use of a resistive sensor less reliable in such conditions. Therefore, understanding the ionic processes occurring at the sensor electrodes is essential to improve measurement reliability. Even in the absence of an external electric field, H\({}^{+}\) and OH\({}^{-}\) ions naturally exist in small, equal concentrations in distilled water due to the self-ionization of water molecules, as described by Equation (5):  
\[\mathrm{H}_{2}\mathrm{O}(l)\rightleftharpoons\mathrm{H}^{+}(aq)+\mathrm{OH}^{-}( aq) \tag{5}\]  
However, when a voltage is applied across the sensor, ion migration occurs. Although distilled (or condensed) water contains very few free ions due to its high purity, the applied electric field induces the movement of these ions. H\({}^{+}\) ions migrate toward the cathode, where they gain electrons and form hydrogen gas, as described by Equation (6):  
Figure 2.0  
Conversely, OH\({}^{-}\) ions migrate toward the anode, where they lose electrons, producing water and oxygen gas, as shown in Equation (7):  
Figure 2.1  
While positive and negative ions migrate in opposite directions within the medium, they typically do not recombine into water under the influence of the applied electric field, instead forming an ionic current between the electrodes. However, once the electric field is removed, their inherent charge attraction becomes dominant in the absence of the external electric field and these ions will naturally recombine to form water. A common approach to reducing long-term electrochemical effects of electrolysis in resistive sensors is using alternating current (AC) excitation [19; 20], where the voltage applied to the sensor terminals is cyclically reversed at a determined frequency. This neutralizes the electrochemical effects accumulated during the previous cycle, preventing charge buildup and unwanted ion migration. Another method is pulsed DC excitation [21], in which the sensor is powered intermittently with controlled pulse durations, minimizing the duration of electrolysis while allowing ions to recombine between pulses, and thereby reducing charge buildup and mitigating long-term electrochemical effects. Other approaches to mitigating electrolysis effects include sensor designs that minimize the electric field intensity by increasing electrode spacing, using interdigitated geometries, or the inclusion of neutral or guard electrodes, helping to reduce unintended electrochemical reactions [22]. However, the goal of this study is to explore control-based strategies to mitigate the electrolysis effects observed in sensors designed and tested in previous works. Sensor design modifications will only be considered if these methods prove to be insufficient in addressing the issue. While AC excitation is effective, it typically requires additional circuitry. In contrast, pulsed DC excitation can be implemented using standard microcontroller-based systems without requiring modifications to the existing hardware. Given that the sensor infrastructure developed in previous studies [16; 18] was based on DC measurement techniques, pulsed DC excitation was selected for this study. It offers simplicity, ease of integration, and reduces electrolysis effects while maintaining compatibility with the existing system architecture.