Efficient RF wake-up and charging of IOT devices using ambient WI-FI signals

Abstract

The internet of things (IoT) is based on the deployment of a wide range of sensor devices in various use cases that include smart cities, autonomous cars, mobile health, and agricultural and environmental monitoring. Sensor devices are usually battery operated and can be located in hard-to-reach areas, which limits the ability to charge or replace their batteries. The main aim of this thesis is to design, implement and evaluate an effective solution for harvesting energy from Wi-Fi routers by converting ambient RF signals into DC output that can be used to wake up the sensor device from a deep sleep mode or to charge its battery. The proposed solution includes two main components: (i) a rectifier circuit to harvest RF energy with a voltage boost, with design options based on both passive and active components; (ii) an algorithm to control the data transmission from the Wi-Fi router in order to generate a signal profile that is suitable for achieving high efficiency in the rectifier circuit. Extensive experimental testing is performed in order to analyze the performance trade-offs as a function of various system parameters including the separation distance between the Wi-Fi router and the sensor device. In addition, we optimize the performance of the proposed algorithm to minimize the effect on other users streaming content from the same Wi-Fi router. We also perform experiments to demonstrate the positive effect of interference from multiple Wi-Fi routers located in the vicinity of the sensor device. Finally, we present a case study on smart farming to demonstrate the functionality and effectiveness of our designed solution in waking up and recharging a sensor that is deployed in a field, including experiments to quantify the impact of losses due to deploying the sensor under ground level at various depths.