Design of a Battery-less Wireless Sensor Node Powered by RF Energy Harvester

Wireless sensor nodes are required to be deployed in remote areas for many applications, such as border security, forest fire monitoring, and monitoring of railway tracks. The major challenge is that these sensor nodes need batteries to store energy harvested from solar panels/mini wind-mills for uninterrupted operation. Batteries (lithium chemistry) have a limited or fixed life span and therefore require constant monitoring/replacement from time to time. Battery replacement is not possible for the above-mentioned applications due to replacement challenges and environmental impact. In addition, such discarded batteries end up in landfills, further polluting the environment. Battery-based energy sources eventually run out of power, but RF-based energy harvesting will continue to operate over the long term. To capture RF energy from the atmosphere, the RF energy harvesting system provides benefits over batteries: i) the rectenna nearly never needs to be replaced, since its lifespan is so long; ii) the environmental impact is "green" (unlike batteries, there is no waste that would harm the environment); iii) always available day and night; and iv) it is continuous but has the disadvantage of low power density and efficiency inversely proportional to the distance. A study has been conducted on harvester efficiency (patch and horn antenna) from different RF energy harvesting sources (mobile phones, Wi-Fi routers, and dedicated sub-GHz sources). Dedicated sub-GHz sources are chosen over other sources due to superior harvester efficiency, which has also been experimentally validated in the CSIR-CEERI laboratory. The dedicated source has an output power of 3W and operates at 915 MHz. The custom PCB has been developed for benchmarking harvester efficiency while connected with an in-house developed antenna. A 9.6 dBi gain antenna has been designed and associated with a harvester that generated 3.3 V for an average distance of 1 Meter—the practicality of the proposed technique validated by using a CC1350-based wireless sensor board as a load.