A Passive Design Scheme to Increase the Rectified Power of Piezoelectric Energy Harvesters

Piezoelectric vibration energy harvesting is becoming a promising solution to power wireless sensors and portable electronics. While miniaturizing energy harvesting systems, rectified power efficiencies from miniaturized piezoelectric transducers (PTs) are usually decreased due to insufficient voltage levels generated by the PTs. In this paper, a monolithic PT is split into several regions connected in series. The raw electrical output power is kept constant for different connection configurations, as theoretically predicted. However, the rectified power following a full-bridge rectifier (FBR), or a synchronized switch harvesting on an inductor (SSHI) rectifier, is significantly increased due to the higher voltage/current ratio of series connections. This is an entirely passive design scheme without introducing any additional quiescent power consumption, and it is compatible with most of the state-of-the-art interface circuits. Detailed theoretical derivations are provided to support the theory, and the results are experimentally evaluated using a custom microelectromechanical system PT and a complementary metal–oxide–semiconductor rectification circuit. The results show that, while a PT is split into eight regions connected in series, the performance while using an FBR and an SSHI circuit is increased by 2.3 $\times$ and 5.8 $\times$, respectively, providing an entirely passive approach to improving energy conversion efficiency.