Water-Dynamics Monitoring Using a Flexible Resistive Sensor and Reservoir Computing

Water droplets exhibit different dynamics upon contact with an object, depending on several factors, including the impact angle and droplet volume. Insights gained from monitoring the dynamics might be valuable in rain-sensing applications for analyzing precipitation and wind velocity. Notably, a resistive-type flexible rain sensor exists, which monitors the changes in resistance with time when a water droplet contacts an object. However, the dynamics sensing mechanism for water droplets contacting a conductive superhydrophobic surface has not been systematically explored, and importantly, the sensors can only be used at a 20° tilt angle. Therefore, this study aims to reveal the sensing mechanism of resistive sensors by analyzing the vertical energy of water droplets impacting the sensor surface. By varying the conditions surrounding the vertical impact, we observe that the minimum resistance of the sensor to water droplets increases when the impact energy decreases at different dropping heights and sensor tilt angles. Further, a reservoir-computing algorithm is developed to assess the water dynamics at different sensor tilt angles, resulting in the successful estimation of the water-droplet volume and wind velocity.