Enhancement of Sensitivity and Accuracy of Micro/Nano Water Droplets Detection Using Galvanic-Coupled Arrays

Abstract

A moisture sensor has been reported that detects invisibly small water droplets and distinguishes their particle size with high accuracy and high speed. This sensor uses narrow lines of dissimilar metals as electrodes, arranged with gaps of 0.5 to 10 μm. The working principle for this sensor is that it measures the galvanic current generated when a water droplet forms a bridge-like structure between the electrodes. In addition, the surface of the sensor was controlled by using hydrophilic polymer, GL, and hydrophobic polymer, PMMA. The study of the relationship between the contact angle, projected area of water droplets and current response from the sensor with a modified surface showed that in the case of GL, the contact angle was small (wettability increased) and the average value and distribution of the projected water droplet area and the sensor’s response increased. This enhanced the sensor’s sensitivity. On the other hand, in the case of PMMA, the contact angle was large (wettability decreased), the area of the water droplet and its distribution became small and the accuracy of discriminating the water droplet’s diameter by the sensor enhanced. Therefore, by rendering sensor’s surface hydrophilic and hydrophobic, the sensitivity and accuracy of the sensor could be enhanced.

Quick and Sensitive Detection of Water Using Galvanic-Coupled Arrays with a Submicron Gap for the Advanced Prediction of Dew Condensation

“…The moisture sensor was very fast at showing an output response in comparison to a hygrometer. The calculated relative humidity near the sensor's surface (black line) reached 100% at a point (dew point = 22.5 • C); beyond this point, the response further increased abruptly due to the formation of water droplets [19]. From this observation, it can be said that it was possible to detect minute and relatively gradual changes in humidity with high accuracy and high speed.…”

“…With a lower spacing between the electrodes, such as 0.5 µm, the sensor can even detect much smaller water molecules [18]. Further, the sensor's surface [19] and the sensor as a whole can be modified to the actual target [20]. By using these features, this sensor is expected to detect dew condensation with high accuracy at an early stage and is catered to the actual target.…”

“…By using these features, this sensor is expected to detect dew condensation with high accuracy at an early stage and is catered to the actual target. We have demonstrated the detection of micro/nano-sized water droplets with a quick response of 200 ms [18] and the improvement of its sensitivity and accuracy via the modification in the surface of the sensor chip [19]. Additionally, we suggested the prediction of dew condensation from sensing behavior at different but steady humidity around 100%.…”

Recent Sensing Technologies of Imperceptible Water in Atmosphere

“…Our recent research works demonstrated the fabrication of a new moisture sensor based on the existence of two dissimilar Au and Al metal electrodes with a comb-like structure that possesses tailored gap size as desired. Whenever a water droplet bridges the two electrodes as a function of dew point condensation, a galvanic response current could be exclusively detected on the sensor surface with excellent sensitivity and reproducibility at a minimum response time of ~20 ms [19][20][21][22][23][24][25][26][27]. This criterion enabled us to beneficially use our MS in many applications, such as (1) accurate spontaneous detection of a tiny amount of water and determination of its droplet size [19][20][21][22][23].…”

“…This criterion enabled us to beneficially use our MS in many applications, such as (1) accurate spontaneous detection of a tiny amount of water and determination of its droplet size [19][20][21][22][23]. (2) Improving sensor sensitivity and accuracy for dew condensation detection while changing its surface wettability [24].…”