The article presents the development of a self-powered rectiﬁed electromagnetic energy harvester (EMEH) under low frequency excitations. To overcome the drawback of low output voltage across the small optimal load, it is proposed to use the transistor-based rectiﬁer biased by the self-powered SECE-based piezoelectric energy harvester (PEH). In addition, the buck-boost converter controlled by the self-powered SSHI-based PEH is im- plemented for the maximum power point tracking. A semi-analytic model is developed for predicting the peak power and the optimal load used for designing the buck-boost converter. The prediction is then validated by experiment showing 1.5 mW optimal output power. Further, it is found that the 0.22 low rectiﬁed voltage is increased up to 2.5 V by the proposed SSHI-based voltage boosting technique. It oﬀers advantages of zero quiescent power dissipation and the ease of tuning the input impedance of the buck-boost converter by varying the SSHI load impedance.
The article presents the study of a novel self-powered SECE (synchronized electric charge extraction) circuit for scavenging piezoelectric energy under low-frequency shock excitation. Specifically, the device consists of a piezoelectric cantilever beam whose tip magnet is impulsively excited by a rotating magnet. It is attached to a load-independent SECE circuit with the advantage of power enhancement at low-level output voltage. The proposed circuit includes an envelope detector for voltage detection, a voltage divider for minimizing the switching delay and a diode for recovering the charge on the detection capacitance. The result shows that the predicted harvested power agrees well with the experimental observations. In addition, the power ripples are significantly reduced due to the larger electric-induced damping drawn from the SECE technique. Finally, the load-independent property makes the observed SECE power remain constant within the output voltage operated at around 2-5 volt, and therefore outperforms the standard DC power.