Wearable self-powered diaper-shaped urinary-incontinence sensor suppressing response-time variation with 0.3-V start-up converter

A wearable, wireless self-powered urinary-incontinence sensor has been developed that consists of a diaper-shaped urine-activated battery, an intermittent-power-supply circuit with an ultralow-voltage start-up converter, and a wireless transmitter. The battery is embedded in a diaper and consists of absorbent material sandwiched between an aluminum electrode and a spongiform carbon electrode, which are safe to wear. The intermittent-power-supply circuit has a start-up converter that boosts the 0.5-V output of the battery to 2 V and drives a DC-DC converter. The two-stage boosting operation from 0.5 V suppresses the variation among batteries in the charging time of a storage capacitor, thereby reducing the variation among diapers in the response time of the sensor. A prototype urinary-incontinence sensor was fabricated to verify the concept. When 80 cc of urine are poured onto a diaper, the sensor transmits an ID signal over a distance of 5 m.