A flexible organohydrogel-based humidity sensor for noncontact artificial sensation

In this paper, we propose a simple organohydrogel based capacitive humidity sensor for noncontact artificial sensation applications. The sensor is simple in design and consists of a transparent polyacrylamide organohydrogel thin film attached on a flexible inter-digit electrode layer. The process of water absorption and desorption is reversible, thus the dielectric of the organohydrogel film as well as the overall capacitance are dependent on environmental humidity. The water absorption capacity and structural reliability of the device have been largely improved by adding glycerol in the organohydrogel network. By optimizing both the glycerol concentration and organohydrogel film thickness, the sensor can respond to cyclic humidity changes in a period of 300 ms. In addition, this sensor achieves a high relative capacitance increase (by 20 folds) in a wide relative humidity range (12%–95%). The sensor also exhibits high stability under different bending curvatures (up to 6.81 mm), wide temperature changes (20°C–40°C) and external pressures (0–8 N). To demonstrate the applications in wearable electronics, we found that the sensor was successful in detecting respiration intensity and rate as well as the difference in moisture content in various objects, i.e., human skin and leaf surface. This sensor is highly sensitive and can be useful in the detection of the widerange of humidity changes.