27.2 An Adiabatic Sense and Set Rectifier for Improved Maximum-Power-Point Tracking in Piezoelectric Harvesting with 541% Energy Extraction Gain

Piezoelectric energy harvesters (PEHs) convert mechanical energy from vibrations into electrical energy. They have become popular in energy-autonomous IoT systems. However.’ the total energy extracted by a PEH is highly sensitive to matching between the PEH impedance and the energy extraction circuit. Prior solutions include the use of a full-bridge rectifier (FBR) and a so-called synchronous electric-charge extraction (SECE) [1], and are suitable for non-periodic vibrations. However, their extraction efficiency is low since the large internal capacitance $C_{\mathrm {p}}$ (usually 10’s of nF) of the PEH (Fig. 27.2.1) prevents the output voltage from reaching its maximum power point (MPP) under a typical sinusoidal and transient excitation $(V_{\mathrm {M}\mathrm {P}\mathrm {P}}={1/2}\cdot l_{\mathrm {p}}R_{\mathrm {p}})$. A recently proposed technique [2], [3], [4], called bias-flip, achieves a higher extraction efficiency by forcing a predetermined constant voltage at the PEH output, $V_{\mathrm {p}}$, which is then flipped every half-period of the assumed sinusoidal excitation (Fig. 27.2.1, top left). To flip $V_{\mathrm {p}},$ the energy in capacitor $C_{\mathrm {p}}$ is extracted using either a large external inductor [2], [3] or capacitor arrays [4]. It is then restored with the opposite polarity (Fig. 27.2.1, top). However, $V_{\mathrm {M}\mathrm {P}\mathrm {P}}$ of the PEH varies with sinusoidal current /.’ hence, the two fixed values of $V_{\mathrm {p}}$ in the flip-bias technique either over-or underestimate $V_{\mathrm {M}\mathrm {P}\mathrm {P}}$ for much of the oscillation cycle (pattern filled regions in Fig. 27.2.1, top right). In addition, none of the prior approaches compensate for $V_{\mathrm {M}\mathrm {P}\mathrm {P}}$-waveform amplitude changes, due to input intensity variations or decaying oscillations after an impulse, further degrading efficiency.