DESIGN DI UNA RECTENNA RICONFIGURABILE PER DISPOSITIVI IOT EFFICIENTI E ADATTATIVI

The trends in technology allow the decrease in both size and power consumption of electronic systems. This reduction in size and power has made it possible for small devices to perform complex tasks and run on low voltages portable batteries. The projected number of deployed Internet of Things (IoT) devices is expected to reach billions in the upcoming years. IoT devices have been equipped with several sensors and can communicate with other devices. Therefore, it is unthinkable that this huge number of instruments can be powered by a battery with all the related problems, such as the periodic battery replacement or its recharging. Energy harvesting is a way to obtain electrical energy directly from the environment. Energy is used in everything by humans, such as gas and electricity, or the physical energy needed to carry out their daily tasks, like walking to work. Each of these activities requires both the creation and output of the energy needed to carry them out. For this reason, in the environment there is a lot of energy lost in the processes from all available sources as heat, light, radio waves, vibration and movement. Radio frequency (RF) energy harvesting is an attractive new technique that relies on collecting ambient RF energy in the goal of repurposing it. In fact, it means taking energy that would be otherwise wasted, capturing and utilising it, and finally trying to exploit it in the form of electricity. The main objective of this work is the design of an antenna combined with a rectifying circuit known as rectifying antenna (or rectenna), which is employed to harvest energy from electromagnetic waves. This energy is mainly utilized to wake up devices with low power requirements, whose function is the collection, processing, and transmission of data. Even though the ambient RF energy is widely broadcasted with many systems, the power density is extremely little in free space. Hence, the creation of a high performance energy harvesting system is a challenging requirement for supporting the small available power densities. In this manner, devices become not only environmentally friendly, but also self-sustaining (using the energy lost in their functionality to power themselves). Furthermore, the rectenna must be reconfigurable, so it must be capable of modifying the antenna input impedance to adapt to the variation of the Schottky diode characteristics of the rectifier. Considering the principle of reciprocity of antennas, the same antenna is spent for data transmission and for recovering the surrounding ambient energy. In this report, after the explanation of the context of energy harvesting, the main objective and the challenges, first an accurate analysis of the state of the art of rectennas is presented. Then the role of the rectifier is exhibited together with its realization through the ADS software, which is an electronic design automation software for RF, microwave, and high speed digital applications produced by Keysight. With the help of the study of the state of the art, the simulation results of the rectifying circuit in function of the input power have been obtained by considering a fixed value of the load. These results are critical to ensure the impedance matching with the antenna. Subsequently, the identification of an interesting antenna structure has made possible via CST Microwave Studio (the electromagnetic fields simulation software) to understand the design methodology and, therefore, which parameter must be varied in order to achieve the ideal case of the reconfiguration. Instead, the final part of the thesis is dedicated to the practical implementation of the reconfiguration by means of an electronic switch and to the evaluations on the total efficiency of the rectenna system. Especially, this research is preliminary to a future experimental work.