Wireless Self-powered Sensor System with Sap-activated Battery for Plant Health Monitoring

Abstract

A self-powered plant-health-monitoring sensor powered by a sap-activated battery that consists of two different types of metal electrodes and is activated by the sap of a vascular plant has been developed as an application for wireless biosensor networks. The battery consists of a galvanized iron nail inserted into a tree trunk and a stainless steel electrode planted in the soil nearby. Its output power is on the order of 1 µW. An intermittent-power-supply circuit with a divided-power-line structure, which separates the power line of a storage capacitor while it is discharging, makes it possible to charge the capacitor with an input power of around 1 µW and to supply power to a wireless transmitter with a power dissipation of a few milliwatts. To verify the effectiveness of the circuit scheme, a prototype sensor was fabricated and tested on a potted pachira tree. The sensor was able to transmit a signal about every 40 min over a distance of 5 m. We verified that the variation in the interval between transmitted signals depended on the water content of the soil around the tree.