Application of thermal energy harvesting from low-level heat sources in powering up WSN node

In this paper, a Thermal Energy Harvesting (TEH) technique with power management circuit to condition the output power harvested from low-level heat energy sources with the intention to extend the lifetime of the wireless sensor network (WSN) node is presented. By using this approach, it can extends the WSN nodes lifespan from few days or even weeks (in a case of batteries powered) up to years or even infinity depend on the heat gradient availability. In this context, low-level heat (below 150 °C) sources survey is conducted to evaluate the amount of heat gradient produced by electronic devices and mechanical machinery, and studies the amount of electrical energy harvested by employing the TEH technology. Peltier elements thermoelectric cooler TEC manufactured by Laird xc31 connected in series was used as thermal energy harvester in the presented circuit. A step-up DC-DC switching circuit based on MAX757 IC. was used as the power management and conditioning circuit to boost up the harvested voltage up to 5V. A wireless sensor node was designed based on an efficient low power microcontroller equipped with a temperature sensor and a RF module powered by the proposed TEH circuit. It consumed an average electrical power of about 50mW in the active mode and about 15mW at the sleeping mode. This node was able to transmit the measured data to the next node every 10 seconds whenever there is at least temperature gradient of 30°C on the Peltier element surfaces. In contra, 7.4V rechargeable lithium polymer battery at 500mAh from KingMax only allowed the node to transmit the data for 3 continuous days.