Unipolar synchronized electric charge extraction for piezoelectric energy harvesting

This paper highlights the interest of a shunt rectifier to improve the efficiency of the synchronized electric charge extraction (SECE) circuit formerly developed for piezoelectric energy harvesters. Compared to the classical SECE circuit, which requires a full-bridge rectifier, the proposed architecture is especially interesting for low-amplitude vibrations generating a low piezoelectric voltage, typically lower than 2 V RMS. We provide a full analytical study validated by experimental measurements to illustrate the high performance of the so-called unipolar SECE (USECE) as well as the impact of the resonator characteristics on the overall performance of the harvester. We also propose a model including the main causes of power dissipation, which is validated experimentally, showing that the power efficiency of the circuit is much less dependent on the vibration frequency and magnitude than classical SECE. The proposed architecture combines the high input power of SECE with the high power efficiency resulting from unipolar operation, reaching more than 75% power efficiency in situations where classical SECE is limited to an efficiency lower than 35%. Our experimental results show an increase of +200% output power obtained with USECE compared to classical SECE, which is due to the combination of a higher input power and a higher power efficiency of the proposed circuit.