Contribuições aos sistemas de recuperação de energia para dispositivos autônomos utilizando capacitor variável.

Abstract

There has been an increasing debate on energy harvesting for applications in low consumption systems during the last years. The search for compact autonomous devices has been growing in the microelectronics industry. Such devices have the capacity to generate their own energy for their supply and they are used in applications like: distant telemetry system, sensor network, passive identification through frequency radio, biomedical implants, among others. The energy can be harvested by means of several sources, such as: mechanical vibrations, wind, human movement, electromagnetic waves, solar energy and heat. This research focuses on the conversion of mechanical vibration energy into electrical energy with the use of variable capacitor and piezoelectric transducer represented by the MEMS technology. The architecture of the energy harvesting circuit has been object of several studies with the intention to attain a major amount of energy. In general, this architecture is built from a charge pump which moves the electrons and the charge return circuit. For the charge return, the circuit uses a switch and a control circuit of this switch to determine the moment when the return should occur. This study presents a new architecture of a circuit for vibratory energy harvesting of low potency using variable capacitor. The proposed architecture reduces the use of the charge return circuit diminishing the switch losses and simplifying the control circuit as well as obtaining a considerable increase in energy harvesting. The circuit architecture for the switch which presents an optimal performance and low consumption of energy is still emphasized. The energy harvesting circuit using electrostatic charges requires their capacitors to be previously charged so that they can operate. Only from an initial charge is that the circuit can harvest energy. Aiming to solve this problem, it was introduced a small piezoelectric generator to supply only the initial energy that the circuit of energy harvesting with electrostatic charges needs. It was mounted an energy harvesting system using MEMS and some measurements of the converted energy were accomplished. It was noticed that the system worked for a long period of time without the need for energy recharge.