Synthesis of Ultra-Wideband Rectenna for RF Energy Harvesting From Wireless Communications Networks

The continuous development of IoT technologies, and especially of the sensor networks involved with it, brings about an increase in the demand for power self-reliance of the relevant devices, the number of which is expected to be huge Perhaps the most popular and low-cost way for the achievement of this self-reliance, is the utilization of RF(Radio-Frequency) energy that exists in the ambient and the method developed for this purpose is termed as RF energy harvesting.The present work aimed at designing an RF energy harvesting system, referred to by the well-known term "rectenna", being capable of collecting power at 1.8GHz(GSM), 2.1GHz(UMTS), 2.4GHz(Wi-Fi) and 2.6GHz(LTE). Rectennas are mainly consist of an antenna that collects RF ambient energy, a matching network (MN) and a rectifier that converts the collected signal power from AC to DC. Thus, the research focused at first on the synthesis of a novel antenna of wideband type operating effectively at least within the aforementioned bands. Then, various voltage doubling rectifiers were designed, as simple ones or of Greinacher type. MNs, composed of LC circuit elements or microstrip stubs, suitable for matching the designed antenna with the rectifiers, have been also deigned and are presented. The optimum rectifing circuit was found to give DC voltage equal to 3.7 Volts for input power 0dBm. Research on the effectiveness of the designed novel rectennas to harvest ambient RF energy, was also made. Indicatively, a rectenna consisting of the designed antenna, a classic voltage doubling rectifier and a miscrostrip stub, as MN, is presented. It was found, through simulations and considering that plane waves having electric field strength of 1Volt/m(amplitude), incident on the rectenna and coming from 85 different Directions of Arrival (DoAs) could give DC voltage reaching potentially at 0.51Volts. Analytical results and statistical analysis are presented in the paper.

I. Introduction

Nowadays, as the energy crisis and its impacts are gradually increasing, the demand of ambient green energy is becoming essential for the sustainability in energy provision both to the industry and to the public. For this purpose, modern research has been focused to harvesting energy from available ambient resources (solar, thermal, wireless RF, etc). Among them, the harvesting of RF energy has several advantages. RF energy is free and continuously present in the environment, coming from public telecommunication networks. Its single drawback is its low power level, as its power density within an urban area is about 0.2nW/cm²-1μW/ cm². For all that, it seems to be an attractive candidate to the emergent low-power technologies. The upward trend of Internet of Everything (IoE) guides us to a world where billions of objects will need autonomous and embedded electronic sensors connected over public or private networks. The massive utilization of energy standalone sensors could make their energy supply a major problem, due not only to the great number of them and the required energy amount but also to the possibility of their positions’ access to be limited (bridges, remote or hazardous positions etc). They are exactly these applications at which the utilization of RF harvested energy could be the solution to the problem. At first the majority of modern sensors operate with electric power of microwatt level and thus the RF power collected from ambient could be enough for them. In addition, the RF energy harvesting technology could be used to wirelessly activate electronic sensors or recharge their batteries, thus avoiding their replacement and eliminating human intervention.