Radiofrequency remote powering of wireless sensors over a frequency range of 863/870 MHz

Abstract

The objective of this thesis is to draw, simulate and optimize a remote alimentation device for a wireless sensor, low power, short range, powered by the energy transported over the RF signal. This signal working at UHF frequencies, in particular at 863/870 MHz. The combination of two key components, that is a rectifier circuit based on using Schottky diodes and a folded dipole antenna at λ/2, represents the main elements for a possible remote alimentation system. The connection of the previous elements forms the rectenna element. This conversion system allows finding a DC voltage, by the energy harvested from the ambient RF power. This direct voltage is destined to an energy storage block, presents on each sensor platform. So, it is necessary constantly provide, to the sensor platform, a voltage flow that is sufficient to keep the device operative, for every working mode. The aim is to maximize the power-conversion efficiency of the rectenna for inputpower level. A comparison between the stored energy and consumed energy, is fundamental in order to achieve a system able to keep the battery charged, for a specific electric load. It will be employed a method of directly conjugate-matching between the rectifying circuit and the folded dipole antenna, so that this matching network, between the two elements, can improve the rectenna efficiency.