Sistema de transmissão de energia sem fio por radiofrequência para alimentação de sensores sem fio

Abstract

The present academic work proposes the study and development of a wireless energy transmission system using radiofrequency to power wireless sensors. The foundation and contextualization were carried out based on a literature review, presenting the history of wireless energy transmission, highlighting pioneers such as Nikola Tesla, and the subsequent technological advancements that made this technology viable for modern applications. Different transmission methods are explored, including inductive, resonant, and capacitive coupling, as well as laser and microwave transmission. Fundamental concepts such as radio waves, free-space propagation, and impedance matching are addressed, along with key system components such as transmitters, receivers, energy harvesting, and antennas. The system components were then defined, starting with the transmitter circuit, which comprises a Phase-Locked Loop for frequency stabilization, a voltage-controlled oscillator, a power amplifier, a band-pass filter, and a transmitting antenna. Focusing on performance comparison, three receivers were designed using different rectification methods, full-wave rectifier, voltage multiplier rectifier with two diodes, and Dickson voltage multiplier. The receivers were developed to operate with a compact antenna suitable for capturing the radiofrequency signal, an LC band-pass filter to filter the desired frequency range, and the rectifier circuit. The radiofrequency signal received is initially converted into alternating current by the antenna and then transformed into direct current by the rectifier circuit. Essential circuits such as the oscillator and the band-pass filter, fundamental for the proper functioning of the transmission system, were simulated. Subsequently, simulations were performed for the receiver system, including the three rectifier circuits and the LC filter. This allowed for evaluating the performance of the filter and each rectification method, where the Dickson voltage multiplier rectifier showed the best performance. Three receiver prototypes were then built using perforated phenolic boards as a base for the components. Tests were conducted in energy harvesting mode and using a prefabricated transmitter, powering the receivers at a distance of three meters. During the tests, it was observed that only by using the transmitter was it possible to obtain voltages above 3V, indicating that the energy harvesting mode, although functional, was not capable of providing the desired power. Finally, the comparative analysis of the prototypes demonstrated that the receivers with full-wave rectification and the voltage multiplier with two diodes did not provide stable or sufficient voltage to continuously power the sensor system. In contrast, the Dickson voltage multiplier stood out for providing stable energy to power the system. Based on the results obtained, it is concluded that for low-power wireless sensor systems, the receiver with a Dickson voltage multiplier rectifier is the most efficient and reliable alternative. Its ability to provide stable energy stands out compared to the limitations observed in the other prototypes, making it a promising solution for applications requiring energy efficiency and stability.