Epidermal Impedance Sensing Sheets for Precision Hydration Assessment and Spatial Mapping

Abstract—This paper presents a class of hydration monitor that uses ultrathin, stretchable sheets with arrays of embedded impedance sensors for precise measurement and spatially multi-plexed mapping. The devices contain miniaturized capacitive elec-trodes arranged in a matrix format, capable of integration with skin in a conformal, intimate manner due to the overall skin-like physi-cal properties. These “epidermal ” systems noninvasively quantify regional variations in skin hydration, at uniform or variable skin depths. Experimental results demonstrate that the devices possess excellent uniformity, with favorable precision and accuracy. Theo-retical models capture the underlying physics of the measurement and enable quantitative interpretation of the experimental results. These devices are appealing for applications ranging from skin care and dermatology, to cosmetology and health/wellness monitoring, with the additional potential for combined use with other classes of sensors for comprehensive, quantitative physiological assessment via the skin. Index Terms—Depth profiling, epidermal electronics, hydration sensing, multiplexing, spatial mapping. I