Skin Mountable Capillaric Strain Sensor with Ultrahigh Sensitivity and Direction Specificity

Abstract

Microfluidic devices filled with conductive liquids exhibit a unique potential to integrate fluid physics and electronics while maintaining low mechanical load (i.e., extremely soft and stretchable) for skin mounted wearable device applications. Here, a novel microfluidic strain sensing mechanism is presented, which provides a theoretically unlimited tunable gauge factor, directionally specific and linear response, and negligible hysteresis for skin deformation measurements. The control over flow dynamics enables signal filtering, thresholding, and basic logic operations to be performed in the fluidic‐domain potentially simplifying the electronic and digital processing components. The capillaric strain sensor technology relies on the ultrahigh electrical resistance modification due to the capillary flow of conductive ionic liquids in response to the elastomeric deformation of silicone microchannels. The directional specificity and ultrahigh sensitivity (e.g., gauge factor > 3000) are demonstrated for distinguishing facial activity types and the subtle differences in facial muscle‐strengthening activities.