A wireless self-powered urinary incontinence sensor system

A self-powered urinary incontinence sensor system consisting of a disposable urine-activated coin battery and a wireless transmitter has been developed as an application for wireless sensor networks. The urine-activated battery makes possible both the sensing of urine leakage and self-powered operation. An intermittent power-supply circuit that uses an electrical double-layer capacitor (EDLC) with a small internal resistance suppresses the supply voltage drop due to the large internal resistance of the battery. This circuit and a 1-V SAW oscillator reduce the power dissipation of a wireless transmitter. The SAW oscillator quickly responds to the on-off control of the power supply, which makes it suitable for intermittent operation. To verify the effectiveness of the circuit scheme, we fabricated a prototype sensor system. When the volume of urine is 0.2 ml, the battery outputs a voltage of over 1.3 V; and the sensor system can transmit signals over a distance of 50 cm.