Tiny Piezoelectric Energy-Harvesting CMOS Charger

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Yang, Siyu
Rincón-Mora, Gabriel A.
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Wireless microsystems embedded in smart homes, industries, and human bodies can save money, energy, and lives. They have to be compact to access difficult places, and their tiny on-board batteries drain quickly to support the functionality. Fortunately, piezoelectric transducer can draw kinect energy from ambient vibrations to constantly replenish the batteries. Tiny piezoelectric transducers, however, only draw a small portion of the energy from vibration. Moreover, the charger is lossy, and imposes limits on the operation. The objective of this research is to study, evaluate, design, build, test, and assess energy-harvesting CMOS battery chargers that draw and output the most power possible from ambient motion with centimeter-scale piezoelectric transducers that fit on wireless microsystems. Among the state of the art, synchronous discharge with asymmetrical pre-charging can output the most power with only one inductor. Pre-charging symmetrically can draw the same or even more power under the same breakdown limit, and loses less ohmic loss because of lower inductor current. On the other hand, direct inductor transfers can further reduce ohmic loss by transferring more energy than the inductor carries. As a result, the proposed series switched-inductor bridge charger that can output 6.8x higher than an ideal bridge is the best synchronous discharge charger. The recycling bridge from the state of the art can draw the most power, albeit using two inductors and a dedicated maximum power-point charger. The proposed recycling switched-inductor charger can draw the highest power using one inductor without the extra charger, can output 12x higher than an ideal bridge and 76% of the theoretical maximum power the transducer can draw, and, as a result, can prolong lifetime and expand functionality for wireless microsystems.
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