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 a 0.3 V 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 with the start-up converter makes it possible to boost the 0.6 V output of the battery to 2 V. The boosting operation reduces the variation in the charging time of the storage capacitor among batteries, thereby reducing the variation in the delay time of the intermittent-power-supply circuit, which contains the storage capacitor. A design method for determining both the optimum input-voltage range, in which the variation in charging time is small, and also the capacitance of the storage capacitor is also described. A prototype urinary-incontinence sensor was fabricated to verify the effectiveness of our sensor. When 80 cm
³
of urine is poured onto a diaper, the sensor transmits an ID signal over a distance of 5 m. The response time of the sensor is 17 s, and the period of intermittent operation is 12-s long.