Energy harvesting is expected to be used as a source of energy for tiny low power sensor nodes. Since the amount of harvested energy is unstable, an energy storage device is used with an energy harvesting system. With advancement in rechargeable batteries, ultra-low weight rechargeable lithium-ion batteries are used as energy storage devices with low power wireless sensor nodes at remote places. These ultra-low weight energy storage devices are expected to be charged efficiently with maximum harvested power. The mismatching of the electrical impedance between input (i.e. Piezoelectric Transducer (PZT)) and output (i.e. Load) gives inefficient power transfer. The piezoelectric energy harvesting circuit described in this paper focuses on the design and analysis of op-amp based inductor circuit for matching the impedance by presenting a conjugate impedance match to the Piezoelectric harvester. The values of inductor obtained for optimal power transfer from PZT to storage device tend to be prohibitively large. This becomes an inhibiting factor for Integrated Circuit(IC) realization of the interface circuits. The proposed work implements the required value of inductor using op-amp circuit to match the complex conjugate part of the impedance thereby making it cost effective and suitable for IC realization. Finally, comparison between pure resistive match and complex conjugate match is presented along with results.

Purpose The purpose of this research paper is to explore the possibility to enhance the power transfer from piezoelectric energy harvester (PEH) source to the load. As the proposed gyrator-induced voltage flip technique (GIVFT) does not require bulky components such as physical inductors, it is easily realizable in small integrated circuits (IC) package thereby offering performance benefits, reducing area overhead and providing cost benefits for constrained self-powered autonomous Internet-of-Things (IoT) applications. Design/methodology/approach This paper presents an inductorless interface circuit for PEH. The proposed technique is called GIVFT and is demonstrated using active elements. The authors use gyrator to induce voltage flip at the output side of PEH to enhance the charge extraction from PEH. The proposed technique uses the current-voltage (I-V) relationship of gyrator to get appropriate phasor response necessary to induce the voltage flip at the output of PEH to gain power transfer enhancement at the load. Findings The experimental results show the efficacy of the GIVFT realization for enhanced power extraction. The authors have compared their proposed design with popular earlier reported interface circuits. Experimentally measured performance improvement is 1.86×higher than the baseline comparison of full-wave bridge rectifier circuit. The authors demonstrated a voltage flip using GIVFT to gain power transfer improvement in piezoelectric energy harvesting. Originality/value To the best of the authors’ knowledge, pertaining to the field of PEH, this is the first reported GIVFT based on the I-V relationship of the gyrator. The proposed approach could be useful for constrained self-powered autonomous IoT applications, and it could be of importance in guiding the design of new interface circuits for PEH.