Carbon-Ink Sensing Patterns for a Contactless Smart Diaper System

To keep up with the care needs of an increasing population in elderly nursing homes, smart incontinence materials promise to reduce care-taking workload, cut costs and increase user comfort. Therefore, we present two carbon-ink sensors designs that rely on a recently patented differential transmission measurement technique. The proposed sensors are low cost and mass producible, printed directly on the disposable diaper and they interface to the read-out electronics via a reusable flexible strip. In a simulation based on the square resistance of the carbon ink, both designs achieve a similar dynamic range, being most responsive to moisture resistances between 1 kΩ and 100 kΩ. In a practical test on two prototype smart diapers, the designed sensors show promising results by detecting a small volume of only 50 ml, with the two sensors designs being 58% and respectively 55% saturated after adding one litre of moisture.