FM Signals-Based Energy Harvester Optimisation for Low

Abstract

Energy harvesting from ambient sources has attracted a lot of research recently due to the high demand for cheaper and greener energy. Several researchers have investigated the possibility of harvesting energy from ambient Radio Frequency (RF) energy sources such as Wi-Fi, Global System for Mobile communications (GSM), microwaves, Code Division Multiple Access (CDMA), Ultra High Frequency (UHF) and even Amplitude Modulation (AM) signals. But in most of these researches, the harvested energy is too low, especially when the energy harvester is far from the transmitting station. Furthermore, very little effort has been directed towards harvesting energy from Frequency Modulation (FM) signals which are abundant in most parts of the world. The energy harvested is mainly used in Wireless Sensor Networks (WSN). WSNs are becoming popular due to their low cost, long ranges of transmission as compared to wired sensor networks, long life due to low power requirements and ability to operate in hard-to reach areas. However, powering these wireless sensor networks has posed a challenge since battery replacement would require constant access to the location of the sensors. The aim of this research was to harvest energy from FM signals and use the energy to power a wireless sensor network. This approach will help reduce the frequency of battery replacement and consequently reduce the maintenance costs, improve safety and increase the overall efficiency of the system. In this study, the signal strength of different signals within the vicinity was investigated. The sub-systems that make up an FM harvester were designed based on the given constraints of the WSN. Appropriate mathematical formulations were used to come up with the values of the components in a passive RLC filter as well as the voltage multiplier. Computer simulations using LTSPICE IV were carried out to verify the operation of the designed filter. The software was also used to assess the effect of stage capacitance and the number of stages on the performance xviii of the multiplier. . An XBee WSN was designed and implemented using an ATMEGA328P microcontroller programmed in the C++ language. The receiver was connected to the computer to receive data sent by the transmitter which was powered by a 3200 mAh rechargeable battery. A graphical user interface (GUI) was also developed to display the data received from the transmitter. The experimental analysis showed that the harvester could produce a maximum voltage of 2.95 V when the optimum system parameter obtained from simulations were used. The output of the harvester was used to recharge the battery in the transmitter. Data collected over a period of 48 hours showed that the harvester reduced the battery draining speed from -16.418 mAh per hour to -5.8315 mAh per hour which represented a 64% improvement in the speed. The battery life was extended from 196 hours to 555 hours, which represented a 180% increase in the life of the battery.