High humidity sensing by 'hygromorphic' dielectric elastomer actuator

Many capacitive or resistive humidity sensors cannot accurately measure high humidity because of surface water condensation and saturation of hygmsopic material in the sensors. Here, we propose a novel method of high humidity measurement using a 'hydromorphic' dielectric elastomer actuator (DEA). This novel humidity sensor consists of a 'relatively water-inert' acrylic dielectric elastomer layer (3M VHB 4910) sandwiched by a pair of hygroscopic polymer electrodes. The hygroscopic polymer electrodes are made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS); they become softer upon moisture absorption while enabling moisture permeation into the dielectric elastomer substrate during electrical activation and readout. While the dielectric elastomeric actuation (under constant voltage) enlarged with increasing humidity, the current leaked through it rose more significantly. This suggests a strong humidity dependence of dielectric resistivity. Experimental correlation showed the dielectric resistance be a piecewise linear function of humidity. Further, this DEA-based humidity sensor remained working when both its electrodes were sprayed with a mist of water droplets.

Automated summary

The novel humidity sensor proposed in this study utilizes a 'hydromorphic' dielectric elastomer actuator to accurately measure high humidity. By using hygroscopic polymer electrodes and a water-inert acrylic dielectric elastomer layer, the sensor remains operational even when exposed to water droplets.