Evaluation of Printed Coplanar Capacitive Sensors for Reliable Quantification of Fluids in Adult Diaper

Advancements in printed technology have led to the development of economical and sustainable electronic solutions for wearable medical devices in the healthcare sector. Printed capacitive sensors in planar geometry are widely used in the development of smart diapers for detecting urination events, quantifying detection, and quantifying voided volumes. However, factors such as the effect of sodium electrolyte variation, body weight effect on a wet diaper and gravitational effect on wet diapers impair the quantification of voided volume with capacitive sensors. In this study, a printed capacitive sensor for quantifying human body fluids in adult diaper was evaluated to analyze these effects. Silver and carbon inks were used to print the parallel-plate capacitive electrodes on a flexible substrate in a coplanar geometry. In-diaper quantification measurements were performed at various concentration levels in pseudo urine with small incremental levels at the adult human urination flow rate. The impact of human body weight on quantification measurements using a wet diaper was studied. The gravitational pull effect of wetness was evaluated for on-human-torso use in both standing and lying positions. It was observed that a printed coplanar capacitive sensor alone is insufficient to reliably quantify the voided volume in diapers.