A Resonant Synchronized Switch Harvesting Rectifier with Bias-Flip Charge Recycling for Piezoelectric Energy Harvesting Achieving 13.9x Power Enhancement

Piezoelectric energy harvesting (PEH) is a promising research topic, offering a practical way to extract kinetic energy to power electronics, e.g., wearable and implantable devices. A piezoelectric transducer (PT) can be modeled as an AC current source,$\mathrm{l}_{\mathrm{p}}$, in parallel with an intrinsic capacitor, Cp (Fig. 1 top). To extract more power from the PT, synchronized switch harvesting (SSH) rectifiers, employing an inductor (SSHI) or capacitors (SSHC), flip the voltage across Cp at the lp zero-crossing moment. Most SSH designs aim to maximize the voltage flipping efficiency$(\eta_{\mathrm{F}})$to nearly 90%; however, a high$\eta_{\mathrm{F}}$does not always bring high output power out since the maximum power point (MPP) goes to an unachievable level, largely exceeding the standard CMOS break-down voltage. Though$\text{low}-\eta_{\mathrm{F}}$designs pull the MPP back to lower voltage, the large energy loss due to$\text{low}-\eta_{\mathrm{F}}$flipping, expressed by$\mathrm{E}_{\text{Flip}-\text{Loss}}=\mathrm{C}_{\mathrm{P}}^{*} \mathrm{V}_{\mathrm{S}^{2}}(1-\eta_{\mathrm{F}^{2}}) / 2$, reduces the output power significantly.